'WORLD HEALTH ORGANIZATION

REGIONAL OFFICE FOR THE BUREAU ~GIONALbE Id EAmmw MEDITERRANEBN

W/FAO SEMINAR ON FOOD HYGIENE, 200NCBSS CONTROL EM&/m.W14 AND VET$RINARY PUBLIC ~~ PRACTIC3 28 October 1964

Lahore,- 29 October - 6 November Teheran, 7 - 11 November 1964

by

3 Dr. M. Abdussdam TABLE: OF CONTENTS

I EPIDENIOII3GICffi NOTES ON HUMAN PJFECTIONS WITH PARASITES OF lWlMAIS

I1 PROTOZOA

VII CONCLUDING mRKS I WIDEMIOLOGICAL NOTES ON HUMAN INFECTIONS WITH PARASITES OF ANIMAIS

A large majorlty of the anlmal parasltes are host speclflc and are not interchangeable between anlmals and man. A few are, however, not so rlgld in them physiological requirements and can parasitize more than one host species including man. Thls small group includes such important causes of human dxsease as Lecshmania, blood flukes, intestinal f$mes, tapeworms, trichinae, strongyloldes and others, Some parasites of animals spend thelr larval perlod in human tlssues and cause such serlous dlseases as hydatldosls and myiasls. In other cases, the larvae that enter human tlssues fall to develop normally and perform erratic migrations causlng serlous damage as in creeping eruption, visceral larva migrans, etc. The ectoparasites acquired from anlmals not only cause annoyance and palnfill skln lesions but in many cases transmlt pathogenic micro'dr@;an~sms. Many of the zoonoses caused by animal parasltes are of -rro&rferabfe local importance in publlc health. Others are of relatively rnlnor importance.

The blo-ecological and evolutionary aspects of the relationships involved have been reviewed by Garnhm (195si Kozar (1959), Cameron (lg*), Heisch (1956) and Wright (1947a). Beaver (1961) and Faust (1955) briefly surveyed the infections resulting from lnvaslon by parasltes of anmals, and Shikhobalova (1955) published a popular account of the helmlnthc zoonoses of the Sovlet Union, In the present artlcle, the principal parasitic lnfectlons Interchangeable between man and vertebrate anlmals have been listed an3 brief notes on important epidemiological features added. Emphasis is laid on recent work and on infections with pathogenic parasites reported from warm areas of the world.

Most of the protozoan parasltes of man, and of the anlmals in his envzromnt, are so strlctly host speclflc that Interchanges of infection are Infrequent even where close morphological similarity between the parasltes of man and anlrnals suggests such a possibility. It is mainly among the haemoflagellates that host speci'ficity is not so rlgld and animals assume the role of reservoirs of human ~nfection. Ii?-@Bl ~WH/14 page 2 All the three established species of Leishmania Leishmaniasis * pathogenic for man [L. tropica L. donovani and L. braziliensis-complex) have animal hosts in nature. Leishmania tropica, the cause of oriental sore, is widely but focally distributed in the dry zones of the tropics and sub-tropics. Endemic areas exist in Africa, the countries around the Mditeranean, Middle East, Indo-Pakistan, Central Asia and China, Dogs have been found naturally infected in many of the endemic areas but their exact role in the endemiology of the disease is not clear, Recent work In Central Asia (~oare,1955; Petrishcheva et al., 1963) has revealed the existence of two types of the disease. A "moi~t'~ ulcerating type occurs in the people of rural areas on the fringe of deserts and is contracted from gerbils (~hombomysopimus, Pallasiomys erythrourus, P, meridianus and others) through the agency of sandflies. The other is a chronic "dry" type, characterized by late ulceration, It occurs in urban areas and represents man to man infection, through sandflies, of the Leishmania which is better adapted to the human subject. The two types are reported to be immunologically distinct. !Pk "moist" variety has also been found in Iran in association with Rhombo~qys opimus (Ansari and Faghih, 1953). It is likely that natural enzootic foci in gerbils and other desert rodents exist in the other infected areas. mis might also explain tlre endemici-ty of the disease in dry areas.

Visceral leishmaniasis (kala azar) is widely distributed in northern and western China, central Asia, Indo-Pakistan, the Middle East, countries around the Mediteranean, East Africa and in a few localities in West Africa and South America. Dogs have long been considered to be an important reservoir of the infection in China, the Middle Ekst and the Mediteranean area, where the disease occurs more commonly in chilhn, In India and Kenya, dogs have not been found to be infected though the epidemiological picture suggests the existence of an animal reservoir (~eisch,1954) whch may be a rodent. In recent attempts to clwif'y the position, Helsch -et al. (1959) isolated a strain of Leishmania Prom gerbils

OaFnham (1962) has pointed out that there are at least four $oms of outaneous leislmaniasis in the new world (espundia, uta, pian-bois and chicklerosular). Each has a different epidemiology and is due to a different species of Leishmania. gl at era nigricauda) in Kerio Valley, Bnya, where human cases had occurred in fair numbers. Thls strain produces heavy infections in hamsters but only transient local skln nodules in man. Volunteers challenged with L.donovani after their nodules had faded were found to be immune. The gerbil strain may be L. donovani or a related species, In China, recent studies (~i,1957) indicate the possibility of the simultaneous existence of the Indian type disease in which adults are attacked more frequently and dogs do not appear to be implicated. Latyshev -et al. (1951) reported the occurrence of Kala azar among reclamation workers in the previously uninhabited areas of the Vakhsh valley in Tajikistan. A search for local reservoirs revealed that jackals, --Canis (~hos) aureus, were naturally infected. These authors suggest that in densely populated towns of central Asia, the dog has taken over the role of a reservoir from the jackah, and--Hoe (1955, has postulated a similar transfer from the fdx to the dog, in ancient times, in the Mediteranean area.

Muco-cutaneous leishmaniasis (espundia) caused by L. braziliensis is confined to central and south America. kgs have been found naturally infected and have been considered to be reservoirs, No wild animal reservoir has been identified but the prevalence of the disease in forest workers suggests such a possibility (~aveyand Lightbody, 1956).

African- trypanosomiases (reviewed recently by Nash, 1960). The less acute Oambian trypanosomiasis (T. gambiense) is restricted to West Africa between latitudes 15' N. and 15' S. of the equator, the eastern limits being Lakes Victoria pnd Tanganyika. The more serious RhDdesictn type (T. rhdesiense) is restricted to eastern Uganda, Tanganyika, Portuguese East Africa, the Rhodesias and the north-eastern portion of MpzambLque. Until recently, there was no direct evidence that a reservoir of either of these trypanosomes existed in wild animals, altho* there was strong indirect and circumstantial evidence that such reservoirs did occur particularly for T. rhodesiense (~avey,1958). Vie latter occurs in thinly populated bush country abounding in wild ruminants and is transmitted chiefly by the game tsetse fly, Glossina morsitans. Infection is contracted when the uniwbited areas abounding ~sm.~14 page 4 in game are visited for h~ting,fishing, gathering beeewax or travelling. Experimentally, it had been shown that T. rhodesiense, serially transmikted in sheep, with secondary lines in antelope and monkeys, had maintained its infectivity and virulence for man over 2) years (Willet and Fairbairn, 1955; Asbcreft, 1959). Heisch -et al. (1958), however. proved directly that game acted as a resemroir for this trypanosome. They were successful in infecting a human volunteer with a strain isolated from a bush-buck (Tragelaphus scriptus) shot in an endemic area in Kenya.

The Gambian trypanosomiasis is less acute and has a greater tendency to invade the nervous system. It occurs Fn relatively well populated localities with few wild animals. The benignity of the early stages of the disease means that man himself can infect tsetse flies (0. palpalis and (3. tachinoides) when going along shaded paths by the streams and across the fords. This man-to-man transmission through the fly may be the reason for the greater adaptation and consequent mildness of-this infection. It has also been shown that T. gambiense is easily transmitted to the domestic pig, producing a gub-clinical infection which may persist for a year or more (van Hoof, Hanrard and Peel, 1942). Other domestic animals, such as cattle, sheep and goats may also carry this infection without apparent symptoms for long periods of time and probably act as reservoir hosts (Craig and Faust, 1955).

Anrericw trypanosomiases Chagas' disease, caused by Schizotrypanum -oruzi is the better known of the two American infections of this group. It iia prevalent in Mexico, Argentina and the Brazilian highlands, but smaller foci of infection are widespread in the rest of central America and nothemparts of South America. In the United States, the infection has been detected in wild hosts as far north as Maryland (~altonet al., 1958) but human cases are rare or absent, Trypanosomes closely related to 5. cruzihave been Pound in monkeys exported from Malaya and Indonesia but human infection has not been recorded in these countries. The domestic reservoirs in America are dogs, cats and children. The wild reservoir hosts include monkeys, rodents, bats, armadillos and opy)ossums, The vectors are triatornid bugs in which the trypanosomes multiply, making them additional reservoirs. In Venezuela, Colombla and Guatemala, there occurs another trypanosome (T. rangeli)- In the blood of man, dog and opossum. It is apparently non-pathogenic or only mlldly virulent for man. Triatomid bugs (~hodnlusprolixus) are natural vectors. Experi;nentally, the Infection is transmissible to -Cebus monkeys and mice (Plfano, 1954>. Plroplasmosis A few asolated reports of the findlng of piroplasms in human beings have appeared in the literature but were generally regarded as misidentifications or findings of artefacts or Jolly bodies. Skrabalo and Deanovlc (1957) reported a carefully xnvestigated case _rf Babesia bovis infectlon 1n a splenectomlzed lndlvidual who had lived and tended cattle in an Infected area. The illness in this 33-year-old patient was characterized by fever, anaemia, haemoglobinurla and chocolate discoloration of the skin. It ended fatally in eight days. Following thls report, Garnham and Bray (1959) transmitted thls piroplasm by xntravenous inoculation of Infected calf blood into splenectornized chimpanzees (Pan troglodytes verus) and the rhesus monkey, and produced a fulminating lnfectlon accompanied by blackwater as reported in the human patlent. They suggest that latent piropfasmosis may exist on a large scale in rural populations in infected areas and should be considered when the operation of splenectomy is contemplated.

Malaria Bruce-Chwatt (1960) has summarized the present position of the relationship between the malaria of man and anthropoid apes as follows: t7The malarial parasites of anthropoid apes are morphologically ~ndistinguishablefrom %he three species parasitic in man. In order to determine the mutual relationshrps between the human and anthropoid parasites, cross-mfectlon experiments have been carrled out. In the case of the falc~parum-reichenoviparasite, attempts to infect chimpanzee from man have been more successful if %he animal was splenectomized. In the case of the vivax-schwetzi parasite, the human strain produced In the chimpanzee a subclinical infection which could only be demonstrated by the subsequent inoculation of man from the ape; on the other hand, man appears to be more tolerant of the chimwee strain, which produces In hxm only a mlld and translent infection. Man proved to be most susceptible to the infection with the malariae- rodhaini parasite of the chimpanzee, which produced in the humaxi host febrile symptoms with quartan periodicity and was carried through several human passages; the Infection of chimpanzees with the huuan strain was' symptomless with scanty paradites. The situation with regard tO the human -ovale malaria is similar to that of the vivu,-gchvptzi.' Malaria of anthropoid apes is, however, limited to a relatively small part of we& Africa and the Congo even though the distribution of these anlmls is more extensive in Africa armh ham, 1954). Further, the anthropoid-apes are rare animals and live at a distance from htlman habitations. They are therefore a relatively unimportant reservoir of huban malaria.

The malarial papasltes of monkey8 were generally regarded as specific to these animals and not t~~issiblethrough mosquitos to man. ~ecently',fiowever, a s*rain of Plasmodium cynomolgi isolated from Macaca irus in Malaya (Hawking et al., 1957) and considered to be a new subspecies, P. cynomolgi bastianellii, by Gamham (1959b) has been found to be readily t~mPssibleto man through the ggency of anopheline mosquitoes (wles et al,, 1960). ~hilr parasite causes typical malaial paroxysms with tertiary beriodicity and appears in the blood as -vivax-type forms with enlarged erythrocytes and SchWfnerts dots* The monkeys exist in relatively large numbers, often in close Proximity to-marr, in many malarial localities. It is therefore important to assess the exaot role of this malarial parasite in the epidemiology of the human disease by intensive parasitological and ecological studies.

Lntestinal protozoa Ehtamoeba histolytica is the principal parasite of this group with a cosmopolitan distribution. Its pathogenic effects are commonly observed in the tropical and sub-tropical countries and are generally associated with the large race of the parasite. Amoebae identical with or morphologically resembling E.histolytlca have been observed in a variety of mammals including dogs, cats, cattle, pigs, rats and monkem (Iiosre,' 1959). In the latter, it is usually non-pathogenic and saprozalc but in South American monkeys, it causes severe morbidity. It Is generally believed that the animal hosts do n6t play an impoftant part in the epidemiology of this infection in man, *-the possible exception of monkeys in South-East Asia, Thfge animals live near human habitations ~ndprsoably const~tutean important reservoir of human infection (caneron, 1558). It has been shom that the human and simian strains. are readily interchangeable between monkeys and man (Dobell, 1931; Knowles and Das Gupta, 1934).

Walkiers (1930) has repozted an unusual outbreak of dysentry in cattle in Isangi, Congo, in which nuxrous E. histolytica-were seen in the faeces of some of the affected animals. Since this outbreak was preceded by an epidemic of a!!oebiasis in hum beings in the same locality, it was thought that the cattle got infected when gra~ingon pastures polluted with hu-nan faeces. Lq Dakar, E. histolytica was found in the lungs of zebu cattls suffering fron brochopneumonia and streptothricosis (~hieryany! Morel, 1956). How infective bovine amoebiasis can be for man, is still problenatx. The ciliate parasite --Ealantidi~n is also a univeral and common parasite of pigs. In man and monkeys it produces prominent ulceration of the large bowel. Human infection is generally believed to have been derived from pigs as most r;rtie:lts give a history of association with these animals. The relativep: 10-7 incidence of human infection compared with the amount oc expoare suysests that man is quite resistant (~aust,1933). Highly resistant cystic forms, which are produced in the bowel of the pig, are not always forcod in the human host. Man is obviously an abnor~alhost for this parasite (czneron, 1956). &en so, large epidemics are not unknown, e.g. one occurred not long ago in Georgia (~ozar,1959). Toxoplasmosis Toxoplacna-- gondil infects a large nmber of species of mammals and birds besides man. It has a very wide geographical distribution and occurs equally frequently in tropical and temperate countries. Serological surveys indicate that one quarterto thr5e quarters of the adult population of various countries have been infected (~eattie,1960). Because of the high prevalence of infection in domestic animals, particularly food animals, it is believed that human infection is derived from animals. Infected meat, brain, faeces, urine, saliva and nasal secretions have been suggested as possible vehicles of spread. Infection by mouth and nasal instillation can be produced in laboratory animals and it has been suggested that in man the main portal of entry may be through the tonsillopharyngeal region.

Transplacental infeution from the mother t~ the fqetus and accidental infection through wounds is known. The mode of infection m animals, except through the placenta, is not knaun. Arthropods do not appear to play any role in its spread. Avirulent strains can be rendered virulent by passage in the miltimammte mouse, Rattus coucha (Lainson, 1955 1. I!mumocy$tis carinii whrch, like Toxoplasma, is a protozoan of undetermined relationships, is aesociated with oases of interstitial non-syphlltic pneumonia especially in children in Europe, Asia (china), North and South America and is probably ~osmopolitan.~Several species of domestic and wild animals are known to carry the Ixfrasites in their lungs as a latent infection and are believed to be sources of the hman infection. In dogs pneumonia associated with this parasite has been recorded. Man to man transmission is known to occur (Jirovec, 1959). Trematode infections of man are quite important in warm climates especially in the Oriental region. This is because of the vast areas suitable for the propagation of mollusc intermediate hosts and the existence of certain socio- cultural factors (food habits and occupationg) which expose man to infection. Because of certain specific requirements of the snail intermediate hosts, the trematode infections remain endemic in well defined areas, often with recognizable topographic characters. Some trenetodes use a second intermediate host, which may be a food animal (fish, crustacean, etc.) or the infective cercaria may encyst on a food plant (water chestnut, water-cress, water caltrops). Such infections are limited to populations eating these animals or plants raw or undercooked. The following infections may be mentioned:

Oastrodiscoides hominis is a common parasite of man in Assam and also occurs in Indo-China. It causes mild colitis and diarrhoea. In Assam and other para of eastern Indie,- it is connoon in domestic pigs and has been recorded from the Napu mouse-deer in Malaya (Khalil, 193). It does not appear to be an important parasite of man except in eastern India.

Schistomomiasis. The blood-flukes are among the most important parasites of man which infect nearly one-fifth of the whole-human race (Cameron, 1958). In the western Pacific region, Schistosoma japonicum is easily the most important parasitic disease and is considered to attack ovep-46 million people (Stoll, 1947). (Uright, 1950, estimated the number of infected persons to be over 33 million). The infection is widely distributed in China, Japan, Taiwan, Philippines and the Celebes. The infected localities have been listed by Wright (194aa.d1950) an3 more are being added by recent workers (Pesigm -et al., 19583 Okoshi, 1958. and others). Four or more species of the amphibious snail genus Oncoraelania act as intermediate hosts. It has been known for a long time that a number of domestic and wild mammals in the endemic areas are infected with 5. dapanicum and are capable of passing viable eggs which can infect clean snails. These animals include cattle, buffaloes, goats, horses, dogs, rats, moles and weasels. Although the true relative importance of the various hosts in maintaining infection is not fully known, it is clear that it varies from one locality to the other. It has been suggested (McMullen and Harry, 1958) that in Japan and China, cattle are more important than man in maintaining the infection, while in Taiwan pr/s~~.VPH/14 Page 10

a strain of purely zoophilic type shows an incidence In snails comparable to that found in other areas. It has been shown experimentally by HsU and HsU (1956) that,this straln has become so specialized for animals that in man it develops in the viscera for a tune b~tdoes not attain maturity. In the Philippines, recent studies on egg production, hatchability of eggs produced in different hosts, and the mpulation densities of the various hosts indicate that, in Leyete, man is probably the greatest contributor to the infection in snails. As the Oncomelania snails which are amphibious rlischarge cercariae only when in water, it is the vertebrate hosts which go into water that are more commonly infected. Thus, cattle which work in rice fields and dogs which roam about unleashed are frequently infected (Okoshi, 1958). 'Adult water buffaloes i are resis,tant, though the young ones are easily infected. 'In general, it may be stated that vertebrate reservoir hosts other than man appear to &y an imwrtant role in the epidemiology of S. japonicum Infecti6n. though the relative importance of different species in maintaining the infactipn remains to be studied in many localities. There are occasional reports of tbe occurrence of S. J@~pn$+cuminfection in man in various parts of ~f'ricd, (Causton, L930; Maclean =., 1958). Walkiers (1928) described an allied form 8. faradjei from five Coqgolese. It has been suggested that all these wem-spurious or real infections with -S. margrebowef which is conanon In anteloms in southern--%&@i'aaf~~n, 1960).

Schistoso~matisoni infec%kdasldely dlatributed aver Africa and South America. until recently, the lnfectibh was conadered to be largely confined to man, the only recorded animal hosts being two African monkeys, Cercopi'thecus sabaeug and C. aethiops. In recent years, a number of wild ,-1s of the orcler Radentia and some of In$ectivora end Marsupialia hav,p been fomd to be infected in Africa and South America (Kuntz, 1955: Martins, 19%; PLtchford, 1959). More recently, Miller (1959; lw), Nelson (1960) and Strong et al., (1961) have demstrated natural infections in a large percentage of baboons (~apiod,oguera) in endemic areas in Kenya. Nelson believes that these animals derivM their infections from man and my, llfider certain conditions, act as a source of increased transmission to man. -Tt amears that many animal hosts might play an important part as reservoirs of S. rnansoni infection, but further work is needed to el~cidatetheir precise epidemiological significance. EM/SEM.VPH/~~ page 11

SchiLtosoma haematobiurn of Africa and the Middle East, with -1wlated small f6ci in P6rtugal and western India, appears to be rather highly specialized for parasitism in man. An early record of a wild mammal being naturally infected is that of Cercocebus torquatus atys- by Cobbold in 1869. As pointed out by Martins (1958), the identification of the parasite in this record is doubtful as, at that early date, no gthep species of the - complex were horn, and so a mis-ieentification was possible. A few species of this5 complex are 4eacribBd frw animals in Africa and Asia (s, ,bov5, 3 mattheet and S, lgdicum) and are connon among domestic ruminants. In Africa, human infections wi'th all these species, except S. fndicum, have been recorded on the basis of eggs detected in the faeces. Of these S. mattheei is fairly comn in man in parts of South Africa elso son, lga). S. rodbaini which is a comn $amsite Of wizd rodents in Afrlca and 1s now known to ocqur in man in the Conga (~eport,1960)~ fR R~ux(1949) and Varma (1955) have both suspected that the autuchthonhs cases of htmm schi8$osomia~is~n Indo-Pakistan may be due to vFkich is widely prevalent ~x~z,ng_ruminantsand equines in this autl-continent. Fmther $%dies are needed to elucidate the role of these species in human infection and their biological relationship to t&e morphological~yslmilar S, haematobiurn,

Schistosome dermatitis. The blqod flukes of several vertebrates such as birds, rodents, monkeys and other mammals (Trichobilharzia, Pseudobilharaia, Schistosomatiurit, Skhistosoma, etc.) are capable of penetrating the human &in as cercariae but fail to attain maturity in that3 host, After first exposure to such cercariae, there is little observable reaCtioA atd'0livier (1953), on the basis of experiments in monkeys, believes that they reach the lungs and produce small haemorrhages but are killed withln five da:rs. After repeated exposures, however, the'XuW"mnn sh~san allergic response and the cercariae are killea .and retained in the epidermis; They cause severe ~tching,oedema and haemrrbages. Schistosome dermatitis (swimmers1 itch, cercaria dermatitis, etc.) has been observed in several countries including South Africa (de Meillon and Staffberg, 19543: XP mdayai Buckley (1938) found that the cercariae of S, spindale, a blood'fluke of dbmegtic ruminants, Qpoduces an itching dermatitis on thg, feet and hds of rice field workers. A similar copd5tion exists in India (~nantarm,1958) and Burma, It is prababJe that schistosom demtitis is cosmopolitan in distribution. In any case, it is much more widelx distributed than the blogd'flukcs which attain maturity in q. C>onorchiasis. The Chlnese llvcrfluhe Cl-onorchis sinensis, like other h ------members of the family Opisthorchldae aM the c16SZIp a'fTIxWFI~~tCPae,uses fish as the second intermediate host. The infective metacercariae are encysted in the flesh, gills and the skin of the fish. The adult fluke therefore occurs in the fish eating mammals, such as dog, Cat, YiF;-vriTb'mr+martfn, badger and mMc. Hutnap beings get infected through eating raw or undercooked fish. The infectio~lis endemic-Xn JapSz'China (except the north-west), Korea, Taiwan and Indo.China. It hag also been Cetected in Chinese imigrants to other countries (USA, Cuba, India) and in naZiCe Rawaiians who are believed to have been infected through -eating fish imported from dhina or Japan. However, the infection does pok appear to have gained a foothold in thewbies. The fish intemdiate .hosts consist of 40 or more WeSh-wste* species of the f'arnilyCarikrf5ae. In &uyl China, the ide (ctenopharyne;oclbn-- -- ldellus) is the most comn douPe6 of infectlop.

~Dplsth4zyhiqs~is. Three species of OpisViorchis celineus, 0. VWerrini a& Q., neverca), oeour $n the bLle ducts of w, and, like ,Clonorchis, ,use\fishes tmksecond atemaate host$. ,,O,&f&_l= is hinhly endemic in certafmfareas of East ,Fmssia, PQ~@and ,the WSR, It has also been reported from Jam, Indo- China, Philippines and Indo-Pakistan, but is not endemic in localities where clonor&iasis is prevalent. Stoll (1947) has 'eaB%hat;ed-tkat-Urnillion persons are infected,' maikly 1% &-g25Gem Europe and the OSSR. -0. vive&bi, first described from the civet cat (Pelis.-.- viverrinir_ Pe-a~-ir@ert~mk+abasite crf man in nOrth-east Thailand (Sadun, 1957) and western ~ietMinh (~edierand Chesneau, 1924). Sadun has estimated that at least one-fourth of the total population of north-east. Thailand (1,500,000 people) are infected, thus cieatXng a serious publfctfiealth problem, Dogs an4 cats are the reservoir hosts. Opisthorchis nolrer~a-%sa rare parasite of man in Iridia, though it is fairly common in dogs and fl& (Ww~,1931

&her qxlstbmbid flukes, which are rare parasite@of man and are likewise a&&&@ a&&&@ .- &r&&-- eating raw f$sh are ,+F fol$orps: - dkcu* 3n'@%e~i.a,~the reservoir hos$s being, the seal, cat, dog, fox and wolverine (OulrJ 'b'b're&f&). , -Metom&&s o&wtqlis is contracted from eating the fish Pkeu&WasbtrPa pm- inr Japan. Metorchis conj,c?s infec$ion is contracted in the north-eastern part of North America from eating the common sucker

(Catostomus conunersoniL). An allied species, ---CMetorch29 felis occurs in China but does not appear to have been recorded from man. Heterophyiasis,,- The hete2ophyids are small fl~k_es--~aldi$i-~-~e_- --intest~ne of mu?, fish-eatlng msuunals and birds. Their llfe-kycle inmlves snails and fresh-water fishes as intermediate hosts. They-ar%-particularly prevalent in the Nile delta and the humid regions of the Far East. Practically all species are potential parasites of man, but fourteen have so far been found in this host. Two of theas, -Heterophyes _- heterephyes and Metagonimus yokogawai, are the mb~t~important. -Heterophyes heterophyes is Fairly common in Egypt, Palestine, Japan, Korea, central and southem Uhina, Taiwan and the ?hiZ&ppines. The fish hosts are the mullet (~uglljaponicus) and Acanthogobius in Japan ernd * M. cephalus as well as Tilapia nilotica in Egypt. The snails involved live in brackish &aters. Cats, dogs, foxes and other fish-eating mammals are reservoir hosts.

Metagonimus yokogawai is counon in Japan, Korea, Taiwan, China, Siberia, and Indonesia. It has also been encountered in Palestine, Russia, Rumania and Spain. ?he reservoir hosts are dog, cat, pig, the pelican and other piseivorous birds. The fish hosts are the salmonoid, Plectogloss~saltivelis, and the cyprinoids, Richardsonium hakuensis- and Odontobutis obscurus.- Other heterophylda of man, havrng a limited distribution in the Far East, are as foIlows: Heterophyes katsuradai- oceurs in Japan and uses the muLlet as its fish host. H. brevicaeca has been found In man in the Philippines, J&plorehis -taichui and H. pumilo occur in Taiwan and the Philippines, Their fish hosts are Cyprinidae, Siluridae and Colitidae. -Centrocestus formosanus oceurs in Taiwan, the Philippines and Hawaii. There are a few other rare species described mainly from Taiwan.

In their intestinal habitat, the hetcrophyid flukes hardly cause any symptoms unless present in large numbers. In the Phillppinss, however, a generyrl secondary invaslon of the heart, spinal cord, brain &nd other organs has been reportsd in patients harbouring adult heterophyids. Apparently the ova gain access to the general circulation and Invade the capillaries of various organs particularly the heart and brain. In these locations they set up serious cardiac and cerebral lesions, chiefly haemorrhages and deckma. Watson (1960) mentions the flnding of a cyst containing adult Heterophyes removed foth the brain of a man with epileptic symptoms. He had apparently acquired the infection while serving in the Far East. * Salted mullet (fessikh) is often eaten raw ln "&e Near East. MetacemariW remain infective in it for ten days but not for two weeks. Eohinosbmatid infections. These flukes are small and of low pathogenicity for men. Twelve species belonging to the genera Echinostorna, Himastha, Paryphostomum and Echinochasmus have been recorded from man, mrsstly in the Fw East. Some of them may be mentioned here. Echinostoma ilocanum occurs in the Philippines, Celebes, Java and China, in man, dog and rat. The first intermediate host is 'the small anail By-ra~~lwrs:c~~exiusculus. - Tb mcond 'IntermedLate*host my be any fresh-water snail but human infection is derived chiefly from-. This ahail is eaten raw by the inhabitants of Lueon, either darectly from Me shell in the field or with salt or vinegar in the home. Echinostoma revolutum is a cosmopolitan parasite of ducks and geese but haman infection haspbeen rftcorded in Taiwan (2.8 to 6.5 per thousand) and Indonesia. Snails are the second intermediate hosts also. Echinost--2 ralayanurn infects man in Malaysia, Indonesia and China and uses Indopl-anorbis exustus and other freshwater snails as intermediate hosts (Joe and Virik, 1963).

'PBQphostornum sufrartyfex is a parasite pf pigs in eastern Jndia (Bhalerao, 1931) ahd is known to occur in association wLth hpsy and anaemia in children in

Fascioliasis. The ruminant liverfluties -..-Fassiola hepatica anQ-F. gigantics are capable of infecting lnan accidentally. The former.1~generelly prevalent 4 in Europe, ~mericaand the temperate parts of A la. -F. gi~anticais widespread in the warmer parts of Asia, Afrlca, the Pacific Islands and possibly Central Amc?rica. Snails belopging to the family Lyumaeidae are-the most important intermediate hosts. Dotneetic herbivora and wild rabbits are important reservoir. hosts. Human infection takes place through ingestion of infected water plants. s.g. water-cresg (Alicata and Bonnet, 1955; Coudret and Triozon, 19137)~ lotus stem$ and flowers. Rarely, children are infected through eating windfall fruits picked up from enail infested ground. Only sporadic cases occur in man but in a few areas,(France, USSR, Cuba) substantial local foci have been detected. Since oua of ~pseflukes may be passed in the faeces of uninfected persons after eating infected sheep livers, care is necessary is interpreting results of faecal examination. In Africa, human fascioliasis is known from Congo, Mq"nbique and South Africa- (muw & Wilkie, 1956). EM/sm.VPH/14 page 15

In some Eastern Mediterranean countries, sheep and goat livers are habitually consumed raw. It is believed that if livers contain inmature -Fasciola they get lodged in folds and crypts of the buccal and pharyngeal mucous membrtlnes, tonsils, and sometimes in the Eustachian tubes. They cause inflammation of these organs which may be severe and may rarely end in death. The syndrome is well known to the people of 6hese areas and is locally called -halzoun atso son and Kerim, 1456). It is not caused by the adult flukes (Azar, 1%&), An intestlnal fluke, Gtinostomum complwtym, normally parasitic lin fish- eating birds has been found in the pharynx of man in Israel and Japan but it does not cause halzoun. Linguatula larvae have been considered to cause this condition.

Dicrocoeliasis. The small liverfluke of sheep and other herblvora, D~crocoeliurndendriticum is almost cosmopolitan in its distribution. Sporadic infections of human beings have been reported from several countries Including North Africa, Conga. andNigeria. Curran and Feng (1930) demonstrated eggs of this fluke in the faeces of many persons in Shensi Province, China, but believed that most of them were cases of spurious parasitism. The life history of this fluke has been worked out by Krull and Mapes (1951, et sea,) in the New York area. They found the first intermediate host to be a land snail, Cionella lubrica, and the second h6st to be an ant, Formica fusca. AniwLs are infected by swallowing ants carrying the metacertariae. The mocle of infection of human beings is not known but it iS likely to be similar to that for an-1s.

Eurytrema pancreaticum, a dicrocoeliid parasite of the pancreatic and bile ducts oT, swine, cattle and hffaloes &a the Orient, has been reported once from man in Cgina. The llfe history of thls fluke and the mode of infection are similar to those of D. dendriticum. In Mauritius, the land snail Ma&rqchlamys in?ica and the ant Technornyrmex deterquens are probably employed as intemediate hosts (Le Roux and Darnes, 1955).

Fasciolopsiasis. Fasciolppsis buski, the large intestinal fluke occurs in pigs in ChLna, Taiwan, Indo-China, Thailand, Indonesia, Burma and India. It has also been found in wild boars (SUS cristatus) in West Pakistan (Abdussalam-d Amin, 1955). Human infection has been reported from, all these countries except West Pakistan, but the incidence is particularly heavy in Chekiang and ~iangsi Provinces of China (Hsii and Li, 1953) and m certaln districts of Assam. EM/SEM.vpH/14 page 16

Stoll (1947t.estir~aW miUlon Wec$i.onS in the Far East, bW of which are in Chelcf mg area only, Xt Is highly probable that undete~tedfoci 4f human Lnfection exist in other countries where tbe iqfection is known from pi@, aqd water plants grrming in the habitat of snail intermediate hosts are peeled with teeth or, eaten raw. S~lche focus was recently found in central Thailand, here epidemiologicbl TnvuJGtBgations Were carrieb out followdng,the death of a 15-yea~oldgirl who carried over 500 adult Fp buski in her bowels ($adun, 1957). Thlrtken per cent. wf lii-63 pezsons examined i~ar-8 where water,caltrop, {Tram and Eichhornia sp.) was comn were found infected. The prevalence rate was higtre&C among children 5 to 14 years old. The infected children admitted that they often picked up and ate fresh water caltrops on then way to and from school, In heavily ,infected endemic areas, fasciolopsiasis is an important

cweof d.i;sease and death. Animals other than pigs and wi-~d-bwkm attrs not important as reservoirs of the parasite, though dogs are -otcasicmea$--Id8c%ed.

Paragonimiasis. !The 1unglEluke Paragonimus westermani is widely but focally distributed in several countries. In the western Pacific and S.E. Asia, it occurs in Siberia, Japan, Korea, Manchuria, China, Tqiwan, Indo-China, the Philippines, ~hai&g@~ Malaya, Indonesia, India* blew (Puinea, Samoa and the SalomonTslnnd~.~. It is also known from a few areas in Africa in on go, Nigeria, Cameroons) and Central and South America, but it is not known if the infection is en&emically established here except in the Cameroons where 4 per cent. of the population are said to be infected. Records based on the recovery of eggs alone without identification of the worms may be misleading. Yarwood and l3l.u~~(1943) reported the finding of Paragonimus BBggK* a -s cyst behind the ear of a. patient in Nigeria. Fain and Vandepitte (1957) found ------_dmlktr cmts with eggs in people in Kasi, Congo. One of the cysts cohtalned also an adul;t fluke &$ch they _described as repreSein- a new genus and- species, Poikilorchis congolensis. Apart from a snaJl, me-fluke uses aiimcmd intermediate host which may be a crab or a crayfish. In the western Pacific region, crabs of the genera Eliocheitir,- ~atambPl,and.~esaqwi-auSd~ the orayfish A. similis are infected. Human'infection resulT;S from eatll%infected grabs __C__ or crayfJshes particularly after &%rig them raw in vmegar, brine or wine. While the crabs are killed by this treatment, 'he metacercaraiae surfive for several hours and may be vidble when ingested. Certain aborigines in Asia eat the infected crustacea raw. Stoll (1947) has estimated about 3 million cases of lung fluke infection in Asia. The animal hosts of the lung fluke include dog, cat cat, wild cat, tiger, fox, marten, badger, mink, rat, muskrat, weasel, opossum, wolf, goat, pig, crab-eatmg mongoose (Herpestes urva) and the Indian mongoose (H. edwardsi). In man, the fluke generally lives in cystic cavities in the lungs but, at times, it has a more generalized distribution in various organs of the bay. Serious symptoms are produced by the parasites located in the brain, particularly in children. For a comprehensive review of paragonimiasis, see Yo@@awa, Cort and Yokogawa (I*).

Cestodes or tapeworms are highly specialized parasites and use two or more hosts for their development. Species which develop as adults in man spend their larval stages in food animals (and some tapeworms of carnivora infect man during their larval stages). They are, therefore, important as meat-borne infections and their prevalence in any population is connected with their food habits. A few others generally occur in monkeys, rodents, dogs and other animals and accidentally infect man. With the exception of a species of Hymenolepis they cause sporadic infections. The following infections may be mentioned.

Taeniasis. The pork tapeworm, Taenia solium, is cosmopolitan in distribution and is particularly prevalent where insufficiently cooked or processed pork is eakby man, It does not usually occur in Muslim and Jewish cgmnities who do not eat pork. Stoll (1947) has estimated the number of Infected persons in the world to be less than three million, half of them being in Asia. Faust (199). however, considers this estimate to be "ultraconservative". The larval worm eaten with pork develops into an adult in about three months and may live in the intestine for as long as 25 years. Human beings can also be infected with cysticercus if they swallow eggs of the worm harboured by themselves or by someone else. The cysticerci occur most frequently under the skin and in the brain. They may also occur in the muscles, the heart, the liver, lungs, urbit or the abdomen. When in the brain, the cysts cause symptoms of epilepsy and other nervous disorders (~ickerstaff,1955).

The beef tapeworm, Taenia saginata, is considerably more prevalent than the pork tapeworm, Stall's (1947) estimate of its incidence belng 39 million persons, mostly in Africa* and the USSR. The Muslim populations of Asia are also fairly * See Merle (1959), Biche and Thienport (1959), Marsboom -et al. (1960). m/sm.VPH/14 page 18

heevdy Infected Bnd. In the Far &st ~t IS much commoner tban T~-~o&~-ujllUjll.

The 'inc~eence2s ~larkedlyhrgh where $ed?le eat beef cooked 112 lumps'on

open fsres and pollution b-f >ZXiXr2"-wlth hul>cn excreta 3.s freqven% (e.g, ln

Tibet a~dA%y sslnln) Cntt2.e acquire the xn, ectlon from graalns on ground

?olluted by huh1an fae'ces 'cohta~nlns'egg 6 ofcs%h8~"taijzctio?tn. Eggs nay Pemaln

viable bn 'grass for elght weeks or nore. Infecti-on rn water bufraloes IS

sald to be much less th2.n In cattle. Adult cc.ttle and even calves 11/2

to 3 months of age have been found to be hl~hlyresxstant to emer~mental

~nfect~onIn Eest I-fr~ca(Urguhart, 1.959; Proyd and Iiound, 1965).

-E~datldosls. ---- - The dog tapewcrn, Zchrnococcus- - 2;ranulosus, use s sheep and other herb~vqousanlmzls ln uhlch the larvae, (hydatxd cysts) develo?

from eggs m82lorred with grass an? forace yolluted wlBh ~nfectaddog faeces.

Iian can get Infected wxth hydat-d cysts by swallow~nyeggs of thrs tapeworm.

The h~ghyeastance of eggs to env~ron~ientalinfluences 1s an laportant

factor ~n the epxdern~olo@oaf the dr sase. 'eople who regard the dog as

an unclean anrmal and do not iond'e ~t are less coi=~,lonlyaffected than

otiiers in the same area who have no such rnhxbltlbn (Schv?s>e et al., 196~).

Infectlon cenerally take $ place dur~ntch~ldhood but sy,?~~tomscaused by the

hydat d ap;?ear several yeri-s afterrrards In cdult llfe. The ~nfectxonrs

cos-TO)olrtan but nore frequent IP some rre~sthan In the others, e.g. la

South Auerlca, Australla and New Zealand, the : edrterranean reglon fad; arts

of Afrlca. Stoll (19471 hes est~mzi;ed100,000 xniectlons idainly i'n South

America. Recent studre$ In Triales and South Eastern Unlted States have

revealed rq~rtantfocl 02 hydntldosls. In the teaperate ?arts of*Euresxa,

Jappn (Eausch and Yanashita, 1957) and xn St, Lawrence Bland, '?ilaskaYpisinother

closely allled ta leworm (E, mult-~locul&r~ss) of dogs &id Yo::es i6 srevalent.

It utrllzes nuerotxnc r6denks as its jsfernehafe-hosts'in add~tlonto

herblvora and rian It has been sug-e sted that be sdes the nrlmary sylvatlc

cycle ~nvolvlnyCoxes and voles a do~2:-~11xzted cycle cat-mouse cat lay develop (~ogel,196C). In addltlon to the two ty-71cal scecles nentloned above specla1 races or subspeczes adagted to dog-equlne cycle have Seen

found in Eurone 2nd the ZaSern ;~edlterraneanreglon.

Other larvzl cestodes occasionally parasltlc In rlan lnclude Coenurus

cerebralxs wh~chhas been found In the crenlal cnvlty and blad2er-worn:s of

.mltxcens whlch occur In thc mb-cutaneous t-sae or riuscle s. M. glomer- --4 - -atus and 11, braunl lnfectlons are not uacomjon In some parts of Afrzca ($an, 1956).

Dlahyllobotlirras~s. The broad fzsh tapeworm D~>hyllobothrlum-13%

and related specles are prevalent In the human populations of the northern

temperate zone s of Llerlca, Euro~eand 6sla, I here flskes frori fresh-wzter

lakes forl~an Integral part of the dxet. In the western Paclflc, the

lnfectlon occurs In Slberza, northern blanchurla anl Japan. In the warmer

countries of th~sreyron, lt 1s ex"reme1y rare. Several flsh-eatlng

rcan~r~alslncludrng dozs, cats, bears, seals, foxes, etc., are reservorr

hosts. The clllated er'bryo >bore, whxch hatches from the egg in water,

develops In crustaceans to form a orocercold larva. In fxshes, wh~chfeed

on lnfected crustacca, the larva develops to form a sparganum or

i*$erocerco~dlarve '. Thls 1s ~ngestedby nian,and other mammalian hosts

In the flesh of raw or undercookcd fxsh. The frshe s rnvolved Ire the

plkes, eels, salmons, trout, savber and burbot. In Japan, the rainbow

trout and several other Salrnonldae act as second lntermedlate hosts.

Pollutzon of lzkeswlth untre~tedsewage and faeces of hsh-eetlng luamals

are lnlportant factors ln malritalnlng xnfectibn In an endenlc area. Sporadz

case6 outslde endem-c arezs 1 ay be csused by the inportatlon of ~nlected

frsh.

Sparganosls. The plerocercold larvae (s>argana) of several specre s

of dx.-phyllobothrxid tapeworms have been found In man. The adults are

parosltes or ~~ar~aalsor are un--norm. IIost ccse s of human sparganosls have been recorded in the Far East, but'lt io lrnown to occur m other ~al-tsof the world ~ncludlngUSA, Auszralia, _.frlca, 'Er~t~sliiLuxana and Italy (Euang

& Kxrk, 1962). The adults oi @rpetra erlnacel and related qecles nrs foflnd xn dogs, cat-and xfxld carnivora, Only the larva occurs In man.

Other anlnals, ~arasltlz&dby Ihe larva are iilordreys, pigs, weasels, hedgehozti, rats, ch~ckens,snakes and frozs. ?Ian and these anlmals com.~onlybecome lnfected througli lngestlon o L Cyclops col~talnlngthe procercoxd In raxi water. Iiumcn ~nfectxonalso rccults from eat~nrraw

(fleph of the mcond Inter Ledlate hosts (Tro s, snakes etc.: whrch, accordlny; to Vie~nsteln--et al. (1954+), xs not uncom~onIn liorea. Infection may also be acqulred by applying infected me~&from the second Intermediate hosts as poultices on lnflamed sku or mucous neubranc partxcularly the con3unctlva (I:oudek~er, 1926; Botero and Gsmez, 1958).

Hymenolep~asls. The dwarf tanewora, -nolepls nana, 16 casmopolltan In zts dlstrxbutlon but =pea-s to bc comdoner In warm cllmate8. I3esvll.y xnfected focl have been found xn parts of USSR

(Satnarkand) and Indo-Pakistan. Stoll (1947) estimates 20 mlblon infected persons, two-thlrd of then In Lsla. Ch~ldrenbetween the ages of four and nine years arc more colninonly xnfected than other age groups. Bats and mice are commonly Infected wxth the sanc spccles or a closely allied varlety

(H. nana vzr. fraternal but oplnlons dztffer as to ths extent to whzch rodents act as sources of hunaii ~nfection. Emerlnentdly, chlldxen can be xnfected wlth the murlnc sgecles and vice versa- but certaxn d~fferences In the facll~tyof develo~mentIn the rac~proczlhost have been observed.

It appears that r,lan 1s 0;ic chlef source of hxs own ~nfectaon,though there

IS cp~dem~ologxcalevidence thct xnfect~onof murlne orlgln also t@es place.

An allied tapewora, H. dlalnuta occurs In rats, Gnce and other rodents but accidentally infects man and dog. Thls tapeworm uses several specles Ei ;/ S2f. VPH/14 pa. c 21 of arthropods as ~tslntermedlate hosts These lnclude rat fleas, coclrroaches and the meal-wor~: beetle whlch are llable to contanunate human food. Iluman cases h~vebeen observed xn Japan, the Ph~hlllppnes,Indo-

'akrstan, USSR and several othsr countries.

Drvylldxasls and other tauelrorrn ~niections. The dog tapeworm

Dlpylldrurn canxnum 16 a cosnopolltan paraslte of dogs, cats 2nd wlld carnivora. Human bexngs, particularly children, are accadentally infected through cantact wxth dogs znd cats. It 1s generally assuned that xf an lnfectcd doc llclcs the face of a chlld shortly after crushing an lnfeated flea, the cystxcercold lilay be deposited on the face or hand re ailtlng In the xnpstlon of thls xnfectlve stage by the cblld (Iloore,

1962).

Bertxe'lla studerr 1s a yaraslte of primates but has been found in man xn Africa, South tmerxca, Indla, Indonesia and the Ph~bp-hes. Human xnfectlon is accidental and results fro': swallohnng 1npected orlbatxd rmtes whlch act as interinedlate hosts. Ralkllafina:Itlada::ascarxessxs, a parasite of rats, has been occasionally found as a ~~~~+dentalparaslte of aan an the Phlllppines, Thalland and I.aurltlus. It 1s common m rats In northern

Taiwan. Cockroaches are belleved'to serve.ae-~ntcrmedlatehosts.

Inerxucapsifcr cubenas, another parasxtol of rats, ha8 been-found In man

In Kenya and 1s endemLc In Cuba. The majar~fy0f huiaan infections are in chaldrep gne to three yearsof see.

I~Iostof thc lar~enumber of nematode specxes narasltic in man and anrmals are so host s-~eclf~cthat they are not ~nterchnngedIn spite of

frequent 07portunltles of dolng so. Only a ferr (Tr~chlne*, Drncunculus,

Strongyloides, etc.), occur In nany host s:>ecles ~ncludmzman. Some E. /' VpH/14 pace 22

specles produce dlsease Ln iiian as erratlc larvae though they are rncapable of attalnln?, maturlty In thls host.

Stron~ylorc'la4s. _S_t~*ongylol>essJercoral22 1s a cosmo?olltan 4-A--- parasite of Man, pnrtlcularly In warm and uolst areas wlth poor hyglene.

Its dxstrl'mtlon tenekaliy psi-allcls that of hookworms but -~tIS rare In certaln areas In Chlna rr)nerc hookworms .>re h~ghlyprevalent. Stoll (1947) estimates about 35 rmlllon hurlan ~nCectronsIn the world, of whlch 21 mrlllon are In Asla. an 1s bclxeved to be the chlef source of hls own

~nfectlon. 6h-e condrtlons 01 nolsture and warmth are suitable, the worm can multlply In the soil., thus producrng enorriious numbers of larvae caaable of penetrating the human slrln. One of the cxtraordlnary features of skln mCectxon with Strongylol* larvae IS the a,:azlngly rapxd speed wlth whch tlie burrows advance. mother ~nterestxngfenhre IS the so- callcd auto-lnrect~ongroduced by larvze whlch apparently uature In the mucus-faeces med~unat the anus and penetrate dlrectly lnco the skln of that area producln~urtacarlal swellings rrhlch often take the advancing llnear charac cer of creepxng eru-ltlon (iJelner, 196C). Certaxn primates and dogs a-c found xnfectcd In thc elderac areas but they are consxdercd to have acqu2red lnfcctlon from human reservous. 2clated specles of

Strongyloides occur In domestlc an~rnalsbut they are not capsble of cstabllshlng thenselves permanently In the human ~ntcstlne.

Trrchostrongyllais. The small bursate worm Trlchostrongylus -orxental~s--- 1s a comon paraslte of the rural ponulatlons In Iran and the Far East and probably renalns conflncd to man. Othcr s zcxes

(T.colubrlforca.s, T. probulurus, z'vxrtxnu s, T. axelL e tc. ) , have been found In mn and herbivorous animals In varlous parts of the world ond are belng encou~teredwltb lncrcasxng frecuency In survays of helmnth parasxtes of aan. Stoll (1947) cstxrilatcd the world lnc~denceof trlchostron~yl~asls at 5.5 rmllxon human cases. Watson (1953) has ralsed thls estlmate to 58 millions on the btmw oF-kls-ma-~ience~~ofothers sinee Stall's estimate. He himself 'found 25.4 per cent of 335 persene InfeetkC irt.l%reLh, Iraq. In Iran, Biocca -et al. (1960) detected trichostrorr~yliasis-itl -@$)bf the perso-ed-fn-smt-ereas. ERunan infection is apparentlp aequibecf by ingestion of greenstuffs and water polluted with infective larvae derived from the faeces of herbivora which are the natural hosts. Infective-stage Lbr'vae c&,l&rvive on greenstuffs for as long as 15 months and withst& severe aridity. ffe~bivoraare also readily infected with strains of human origin. Infections in man ggnemlly ligh* and symptomless.

Other trichostrongylid parasites of ruminants lrhich have been razgly found as accidental parasites of man are Ostertagla ostertagi, 0. circme&ncta, Haemonchus contortus and Mecistocirrus digitatus. 'The last rr-d spmz%ete is a fairly common parasite of cattle, buffaloes, she'ep and pigs in FMm, -Japan Malaya, Burnla and India, but has-been seen once ) hwgm f~ecqsin H~ngkong.

Ancylostomiasis. The two principal'hookwoms of m, PIricjFLostomb duodenale and Necator americanus, have both been identified from do~s,cats, pigs, v gorillas and other animals. Even if all tHesk identifications are correct, animals do not appear to play any important partfin the epidemiol-.gy of these infections in man. Three species of animal hbbkwdVriis A. brazilifnse. A...caninum and Uncinaria stenocephala are infrequent or radparasites of the humaRl intestine but frecpently cause local cutanedus re&c%ionsat the site of larval penetration. The larvae of A. brazilienae cause indurated reddish papules at the point of penetrationsfnto humah skfn. In tw6 or three days, nam, linear, wavy, red tunnels, 1 to 2 mm in aiameter, apparently produced by migra,tions of the lamrae become prominent ("creeping eruptionn). The lesions Itch, -qapecially at night, and scratchirigl hay ieah to secodary infection. The most colp~rm location of thkse lesions ik dh' the hands and feet, but they my occur on any part of the body. They' persist' for weeks. Beaver (1957) -#es however opined that the assumption that A. b~ktilrenseka~i~es creeping erupMon is to-Jx? regarded as faulty unless fliflher experimental pro& is fortXcoming. These larvae do not cause creepw eruljtion in the skin of dws, cats, rats, guinea-plm or monkeys, although nodular lesions are pduced on ther&l~of qtonkeys. Creeping eruption'has been recorded frewently in the gulflsta+es Sn USA and probably occurs in the Far J%&and Soutf3-America %&el% A.:&rmUierEje oSCurS. &inan infectibn is usually contracted, aurilng contact of exposed parts of the body with moist earth or sand to which infected dogs and cats have access. The larvae of A. caninum and UncJnaria stenocephala generally set up a transient inflammation af the skin with itching, induration and urticaria in 48 hours. The lesions do not show the linear tunnels of the creeping eruption and-disappear withln a few days to two weeks. Ancylostoma malayanum, a parasite of the Himalayan and Malayan bears has been recorded as occurring in marl*

Ascariasis. Ascaris 1umbricoideS of man and of the pig are morphologically identical 'and similar fobs have been recorded 'from We muskrat- (Tiner and Chin, 1948), squirrels and monkeys. The& is experimental ewtdence to show that the hvand porcine parasites are host specific races and the human parasite does go$ attain maturity an the pig. Cameron (1958), however, considers that in the merate, northern regions, whe3.e swine infections are heavy, the infrequent human infections are of porcine ori,gin.

Toxocarosis. The dog asc'arld, Toxocara cdsis s cosmoplita,n parasite of dp. -%-:he,adult wwm has Once been recorded from the human intestine in Egypt. It is, however, more important as a human pathogen in the-Tai-val stage as the so-called "visceral larva migrans". A very large number of em-ape passed out in the faeces of infect4 puppies three weeks to slx months old. cq~tsas high as L5,OQO ova per gram of faeces have been recorded (Sprent and English, 1958). The eggs are highly resiqtant and may survive in the soil for yearn; they are sticky and adhere to any objects that may come h contact with them. Thus, in a short time, the surroundingsj of infected puppies (which may also be the human environment) become heavily infected. The embryo in the egg moults and becomes the second-stage larva. At this time, the egg is infective and may be swallowed by dogs or human beings (children of dirt-eating age). The lame hatch In the small intestine of the child and enter the blood stream thus reaching the liver, lungs, brain and other viscera. In the tissues through which they migrate, they cause large linear necrotic lesions. ~ltimateiy,they become encapsulated in dense connective tissue but remain alive for many years. Beaver (1958) has studied in Singapore, a typical case of a syndrome known for a long time ~~"txopicaleosinophilla" and considers it to be identical with visceral larva migrans. This conditi~n,Is not gaqfined,,$o ,children. Chaudhuri and Saha (1959) have experimentally set up "tmpical ayinophilia" in a volunteer who -azece~lre&lQO-embryonated eggs of T, canis by mouVn. However, tropical eosidopfiilia appears to be a condition with mltlple etioloky and some other helpinthic ipf-ectlq-ismay also be lmplicated in its causation,

Another syndrome ascribable to visceral larva migrans is an eosinophilic granulima 9f, the eye which has been suspected of being retinoblastoma (Wilder, 1950; Ashtort, 1960) and this suspicion has often resulted in unnecessary &Zftftati~a-the eyeball. OtEBri.@ecies of Toxocara (T.-- cati and T. leonina) are proba5ly also capable of causing the foregoing lesions in man (Gibsortj- 196S)r canis larvae are potentially pathogenic for the pig in the same way as for man (Done -., 1960). It may be added that human Infections with T~xocaraspp. of animals are not errgtic parasitism but w,paratenesis't. This phenomenon is seenin helminth parasites of predators which pass tile larval stage in one or more animals preyed on (~eaver,1962).

Gmthostomiasis. Gnathostoma spinigerum oecura in ths stomgte~,,ofcats, dogs and wild felines in Japan, Korea, China, InBoTCb$n@, Nelaya, Wilapd, Blrzma, Indo-Pakistan and Australia. Several cases df human infectdon with inut~&&e- worm are 'known from the western Pacific, fndo-Chine, Inrj&aiapd Australia. In the oourse of its development, %he worm utjli~est,wo ipte-iate hosts, a Cyclops and a fish, frog or snake. The definitive animal hosts acquire in?>ection by eating the second intermediate host. Mq Is probably infected in the same manner but the worm fails to develop to maturity. Human infection is also possible through accidental ingestion of infected Cyclops. Gnathpstorna hispidum, a parasite of swine and cattle, has been recorded as a pgwaslte of the,sub-cutis of man in Japan (Morisbita, 19241, and China (Chen, 1949), Fop a\ copp~ehensivereview of gnathostomiasls see Miyazaki- Im. Dracunculosl$, The guinea-worm Qracunculus medinensis is a widespread parasite of man in Africa, western Asia ,and South AmGrIca. RareTuman infection bas been reported from Korea and a case in a dog is known from China. Several species of Cyclops act as intermediate hosts and human infection takes place through ingesting these crustaceans with raw water. Tanks and step wells are liable to get infected as affected-humans-and animals-can wade through them or wash themselves on the banks.

Filariases. Filarioid worms have been generally regarded as specific to one or two closely allied host species, but recent work has revealed that certain species (e.g. Brugia malayi) are adapted to living in several hast species. This makes filarial infections, actually or potentially impartant Lympatic' filariasls caused by B. malayi has a widespread but patchy dist~ibutlonin South-east Asia from Korea to New,Guinea and extends westward to Mia and Ceylon. The incidence is highest ig water-logged rural areas where the mosquito vectors find suitable breecing places. Recent work in Malaya (Laing -et al., 1960) has shown that the dusky leaf-monkey (Prssbytis abscurus), the long-tailed macaque monkey (wcaca irus), the pangolin we an is javanica), the wild cat (Fells bengalensts) and the dbmestic cat are all infected in nature. Because of the high infection rate in leaf-monkeys they have been regard& as important reservoir hosts while the infection in the domestic cat is bhieved to be incidental to man. Experimental transmission of the human infection to several animal species has been affected (~desonand Wharton, 1958). B. pahangi a closely allied species of filarial worm occurs in a wide range bf ahimals in Malaya but human infections have not been encountefed inenature, Experfmentay, this worm can be transmitted to human beings (Edeson & Wils~n,$964)- Three other species (B. ,patel, Be-buckleyiand B. ceylonensid are as yet unreeoyted from man. A miorofilaria of man described Srom Madagascar under the name Wuchererfa bqncpofti var. vauceli is morphclog~c~rlly,alliedtq Ej. mqlayi (Galliard, 1959) and may uccp in animals.

haloa of man has been reported from African primates and there are other species of -Loa occurring ih several African mnkeys. Recent work on the possibilities of cross infections between man and monkeys tends to show that under mthriil conditions such cross infection must be rare. There are separate host- vector complexes, the human infection involving man &-the vector flies ~krysopssilacea and C. dimidiata. The simian infection involves the various monkey hbsts and the vector flies Chrysops langi and C. centurionis (Watson, 1960).

Acanthocktlrsnema pepstans and A. streptocerca occur-in several areas of tropical Africa, the former extending also to South America. Chimpanzees in Africa have been found Infected but they do not appear to play any important role in the epidemiology of the human infection.

Tr$s@ivsis. Trxchinella spiralis is a small nematode p~a,siteof the .' muscles and intestine which is able to occur as larva and adult in the same individual. It has a wide host range and occurs in more than 25 mammalian species. HU~EUIinfection is generally contracted from pork. The infection is cosmopolitan and particularly common in North America, the Arctic Regions and Europe. Stoll (1947) estimated 27 million infected persons. The infection is relatively unimportant in the troplcs and in the orient though small epidemics have been recorded in Kenya and Tnailand. Recent work tn Alaska (~ausch,1953) has revealed the presence of Trichinella larvae in the flesh of several species of boreal carnivorous mammals including bears (Ursus and Thalarctos) which are eaten by the Eskimos. The larvae were also detected in white whale and seals but these aiiffmill's bPB71it likely to be important as sources of human infection.

Trichuriasis. The whipworm, Trichuris trichikra, is a cosmopolitan parasite of man which is particularly abundant in warm regions with high rainfall. Its incidence generally coincides with that of Ascaris, like which it flourishes in areas where untreated nightsoil is used as fertilizer. Trichuris trichiura has been reported from monkeys, lemurs and swine but there is no evidence that these animals play any part in the epidemiology of the infection in m. Qn the other hand, T, vulpis the whipworm of dogs has occasionally been found in children.

Angiostrbngylosis . Recently Angiostrongylus cantonensis, a fmgwmn ~f rak~has been found in the cerebrospinal fluid, brain and eyes of persons suff'ering: kmm eosinophilia meningo-encephalitis in Hawaii, Tahiti, Thailand and other counkrles in the western Pacific. Human infection takes place from eating raw carrier hosts like slugs, land planarians and prawns. A dlsh consisting of grated coco-nut and prawn julce ("taioro") is popular in Tahiti and other Pacific ieands. Infection through the skin in persons walking barefoot on infected ground has also been suspected (Alicata and Brown, 1962).

Other nematode infections. Capillaria (~epaticola)heprrtica, E$ paraslfe of the liJer of' rats, mice, nares, beavers, muskrats, peccaries and monkeys has been reported from'man in India and South Africa. Pmbably, the infection is not h~ommofi'in Pat infeoted localities but is not easily detectable except on @sltnhtetd exambatibn.

The kidney worm of dogs and other animals, Dioctophyme reliale, occurs in China, America and Europe. A few cases of human infection are known but the infection is necessarily rare. (This worm is Qe largest nematode known and may attain a length of one metre). Syphacia obvelata, an oxyurid parasite of the large bowel of rats and mice is cosmopolitan in distribution and has been recorded once from a child in the Philippines. Gongylonema pulchrum is a parasite of the oesophagus of ruminants and has been found a few times under the oral mucosa in man in China, USA (~eorgia)and Italy. Dung beetles and cockroaches act as intorme ilate hosts,, 'i', 1.~1z71a callr~aeca,the eye-rA.orm of dogs, cats and monkeys L- - *.'"- '--CI -"--Id has been fount in hulran cyns in C$lna, :;ores and India (~riednann, 1948). A related species, T callforr Lensls has been rcported from man twice Tn the - -- A_-^,.-..- United State?. .------ic~rcllcntera cvlr-slry - -- -- is a pazasite cf African monkeys and has been rccordzd frz~ncn ij E,'--lca, Caucrzia, Israel cr16 South America. An acute abdominal sy-ndrome in pc13sons eating ~nsufl"icieptly-cogkedherrings has been described from -,he :Jethe--lanes. Larvae of a flsh parasite Eustoma rotundaturn were found piercinp; the r.?ll of the s~allintestine (van Thiel -et al., 1%).

Qulte a large numb:? of psrasltlc mites, ticks and insectsare int$ic change33le between vertebrate anlm?ls ,-r.d man. Very of%en;these parasites attack r&? whcn he ente-s endomic arras or vhcn the orig&aZ&&t i%the hu&m envirbnment is t--beent OT d~ad. ..In snmq cases, larval Stages only attack man (chigge~s,magpts, etc ). Very octss, the arthropod paraeites acquired from anlmsls riot only cauc: tlssuc dll;.?i;e ctrd annoyenee but also transmit pathogenic micio-organl~nis. Evidently, mch a vast field cannot be adequately covered in the present revieVv. Gnly the bares- ou'tlines. are glven below:

Harvest mites or c&y147~. Or n=?e than 700 or more species of tromblculid larvh nites 'knom, cniy 46 attack rnm o? dori~.;tic animals. Many of the katter occur in the orle~~tand a fc-r trancrit tsutsugamushi fever or scrub typhus. The princlplal~~~~i~e~& !Ti?ombiculh -- a'c-mshl --- and its variant which bad be~nnamed T. deliensis. IT is widespread frcn Japan to New Guinea and westward to Indo- Pakistan. The rccordce hoats inclule to,-, cat, cattle, insectivores, marsupials and birds but the princ?pzl hosts m nature a?e roc'ents. In the river valleys of north-western Esn::?u, J??an, spccles of --Mlcrotus an6 qpodemus are important but further south, rats arc the most Important hosts. In Japan, the tromblcul~ds ape abundvlt inJuly an3 August and disappear with the onset of cold in October. 0 ' In Taiwan they aq active for a loneer perlod (~prilto ~ovember)and further south, nearer the eq~aSor,tney are rctive throughout the year, their numbers decreasing ,wly In the dry season. In Indo-Paklstan and other parts of southern Asia, they are abundant in grassy ~rcar;a$ the ed~sof forests and in abandoned cultivable land where rodcnts are numerous. Man plcks up infection while passing through infested grass or when resting on ~t. An allied species, T. scutellaris,-- - is believed to be the vector of Schlehito fever whlch has been considered to be the mlld nlnter form of scrub .typhus on Izu-Islancts, Japan. Natural hosts of this mite are i-odents and birds. .b northern Japan, tfie larvae appear from September to Xovember but in the Izu Islands its season extends from September to May (~asa,1974).

Other importarit species which attack man in the oriental region are: Tmhbicula~wiahmanni,-T. - hirstl, --Sch'6n~;astla vanderaandei, S. schllffneri, and Neosch8ngastia americana. They cause dermatitis but have not so far been pfoved to transmit any disease. Trombicula autmnalis and T. alfreddugesi, the two well knawn pest chiggers of Europe and America do not seem to occur In the.6t-ient. FOP further information on chiggers reference may be made.40 Wome~sley.(lS52) and Wharton and Fuller (1952).

Blood sucklng mites. Several species of mesostigmatic (gamasid) mites parasitic on domestic binds and hbuse-dwelllmg (domTdi1ihted)r bisds and rodents, attack m- p~usi-trg-&a~n~~lbites looalized denma48%Ls,~ S6m -of'-&he.rnnet common species are: Dermanyssus gallinae of wild and domestic bi_rd-d,aOOnrithdnyssus -bacoti (tropical rat mite) of rats and other yodents,\&b~,rsa (tropical fowl mite) of domestic and wild birds, Leelaps jettmn pf wLsd rodents in Manchuria, Korea and _Japan, Haemogamasus pontiger of rodents an &La, &frtca and Europe, and Hae.molae1aps g1asgo:osi. -- of rats and mice in the Far East ,wd America. The species oc;guy&-ingon birds have ;been reported tp harbour. the vi.wses of arbor encephalitides and those parasitio on rodents haye beegz found to carry infections of murine typhus, plague, tularaemla and haemorrhagic fever. The exact role of these mites in transmitting infections to man needs fu-We3uc+detion. The mouse mite (Allodermanyssus sanguineus): however, transmits rickettsia1 pox to man in USA and the USSR. It%fcurs in No-th Africa and has also been found on the black rat (Rattus rattus) in InEi2i 'WeHYPalriStan (~bdussalam, 1958)'. -7 Etch mites) or Sa~cuptidae* Speczes of Sarcoptes closely allied to human S.\ scabiei eawe qange dn dgmestic ammals. They my be physiological races of a single species or c1meJ.y aLl$ed varieties of it. .Human beings develop transient scabies after contact with infected animals particularly camels and dogs. The infection disappears aut6iiiaia"f;iE-fiTl~after some tlm ExperTmefftat--%ransml~slon of the goat SaFcoptes to e human volunteer has shown that gravid females burrow in soft human skin, lay eggs and cause localized scabres. The lmae tbathatch are, however, unable to establish themselves on human skin and the lesions disappear In aboyt three weeks when the ahult mites- originally transferred have died. A similarly translent lesion occurs on human skin infected wlth Notoedres -cati. The ltch mites of man and animals have been reviewed by Dublnln (1954). --Ticks. Except for Ornithodoros moubata (species complex) which ~nfests human habltatlons in parts of Afrlca, all tlcks are primarily parasrtes of dorrestic and w~ldanlmals. They are only accidental parasites of man, who 1s aktacked when he vlsits various biotopes llke forest, bushlands, grasslands,_ banks of rivers and animal habitations. Some species (~rgasidae]live ih cracks and crevices of houses and come out at nlght to suck the blood of man and animals. They are vectors of such important dlseases as relapsing fevers, tick typhus, Q fever, tick-borne encephal~tldes, haemorrhagic fevers, Colorado fever, tularaemia, brucellosis and possibly anthrax. Their bites cause local dermatitis and sometimes toxaemia (tick paralysis).

Several species belonging to the following genera are known to attack man: --Amas, Ornithodoros, -Ixodes, Hyalon-;-a, Boophllus, Dermacentor, Amblyomma and Haemaphysalis.

Llnguatulld infections. The adult parasites of this group which infeet man live mainly in the respiratory passages of-dogs and snakes. The eggs are vorded with the nasal discharge and contaminate vegetation (salad% water-cress, grass, etc.). Man gets infected by eatlng or chewing raw infected plats. Rarely, rnfection results from eatlng raw or insufficiently cooked lymph nodes or livers of sheep or flesh of snakes contaming the larvae. -.Llnguatula serrata, the adults of which normally occur in dogs and the larvae in herbivorous animals, occasionally lnfects man. It has been found in the snterlor chamber of the human eye (Rendtorff et al., 1962) and In the tonsillar crypts. The adults of Porocephalus armlllatus occur in pythons and vipers. Human infection is rather frequent In parts of Afrlca and occurs in Arabla,

- - Post-mortem examinations haye rqvealep an inciderice of 23 per cent. in the Congo, 5 per cent. in West Africa and 7 per cent. in the Cameroons. A related form, P. moniliformis, occurs in China, Indonesia and the Philippines.

The bugs (Hern~~tera). The family Cimicidae has about 40 known species of which two are commonly associated with man as bed bugs, Clmex lectularius and C. hemlpterus. The former 1s the bed bug of temperate areas dnd the latter of the tropics. It is not uncommon to find both species in the same country but they seldom occur together in the same house. These bugs can easily get established on colonies of laborato~yanimals such as guinea-pigs and rabbits. Other species of this family are parasitic on bats, and birds and Some are potential feeders on man. Cameron (1958) has suggested that the bed bugs were also acquired by man from bats and birds.

The family Triatomidae has several species of the genera Triatoma, ~utriatoma, Rhodnius, Panstrongylus and Eratyrus which attack man. Ordinarily they infest burrows of rodenta and armadillos, & chicken houses. In the abselflce of these animal hosta they enter hou$es and feedan man. They hide in cracks and crevfces durirjg the &ty and fe_ed a*-night. They transmit Trypanosoma cruzi and T. rangeli to man. The bite of some species is painful. Nearly all occur_ .b the Americas but on species (Tr'iatoma rubrofasciaQ+) is found 5.n Soul& China, Sumatra and Hawaii.

Fleas (siphonaptera) are somewhat host specific even though they attach themselves temporarily to the skin of the host for feeding. They are generally numerous on nest building rodents. Certaln species attack domestic mammals or house rats and mice and are cosmopolitan in distribut~on. Others are restricted to certain areas along with their hosts. Those which attack man in addition to animals are: Pulex irritans (cosmopolitan), Xenopsylla cheopis (tropics), X. astia (Indla, Burma, Ceylon), Nosopsyllus fasclatus (temperate zones, Mongolia, Asiatic parts of USSR) and Ctenocephalides canis (c&mopol$tan). Tunga pemtrans or the chigoe attacks man and other mammals in South America from where it bas introduced to, and became established in Africa. The adult female burroWs Ln the skin and lays her eggs there, causing painful sores and abscesses. The bites of other fleas are practically harmless for many persons but some are sensitive and suffer the formation of itchy, erythematous papules and even pustules. It is, of course, well known that fleas transmit certain micro-organisms and helminths tb man. For a review of the transmission of diseases and infections by fleas, see Jellicon (1959).

Kyiasis. The invasion of living tissues of man or animals by fly larime is called myiasis. Except for a single species, the Congo floor maggot (~uchmerom~ialuteola) which is confined to man, all the others known to attack man also attack animals. Indeed, most of them are more commonly parasitic I* animals, which may be regarded as reservoir hosts. The flies that cause m~ries in rn belong to several families of Diptera and have been described in a monograph by James (1947). Some of the more comn types of myiasis my be mentioned here. The tropical warble fly (~ermatoblahominis) attacks human beings associated wit21 anlm~ls. The female fly deposits its eggs on mosquitos, flies, ticks and other Insects but particularly on the mosquito, Psorophora lutzii. On coming in contact with human (or anlmal) skin the larvae hatch out of eggs, penetrate the tissues and remain In the sub-cutaneous tissue for about 10 weeks or less. he^. cause small swellings which itch. If crushed m situ allerglc reaction may result.

The ox warble larvae (Bypoderma bovls and H. Lineaturn) as well as horse bots (Gasterophilus mtestinalis, G. nasalis and G. haemorrhoidalis) penetrate the human skin and migrate in the sub-cutweous tissue, thus causing a creeping eruption. We larvae of the sheep and horse g~dflies (Oestrus ovis and Rhinoestrus purpureus) mainly attack the eyes of shepherds and others associated with animals. The larvae burrow through the conjhnctiva or the skin to reach the orbital fossa and sometimes even penetrate the eye-ball. Sometime& the larvae are deposited In the nose and migrate to the naso-pharynx.

Chrysomyia bezziana is a calllphorine fly common in the Oriental and Ethiopian regions. In certain areas it is the commonest cause of blown wounds. It also lays its maggots in the nares, conjunctiva, ear or vagina. It will larviposit--on llving animals and man but not on carcasses. The Tumbu fly, Cordylobia anthropophaga of tropical Afrlca deposits its eggs on sand or clothes polluted with animal excrement. The larvae which hatch penetrate the intact skin of man (bare feet) and animals whlch comes in contact with the infested area.

VII CONCLUDIKG REMARKS

In spite of host specifity being the general rule among animal parasites, man is subject to attacks by a number of ~mportantparasites of animals. A large number of them are derived from domestic animals particularly the dog slnd the pig. Of the wild animals, rodents appear to be the most important sources of human mfectlon. Qulte a large number of zoonoses caused by animal parasites occur ?n Afrlca, the Orlental Region and the neimU~rfm-rrreasafthe Far East. Trematode infections, wlth schistosomiasis at the head of the list, appear to be quite prominent in the latter reglon. In controlling these infections, the application of sanitary measures needs to be suppleniented substantially by health education of the people. Many of the infections can be easily avoided by slight changes in food habits and socio-tultmral or agricultural practices. In other cases, the wearing of shoes or certain type of dress may be enough to ward off infection. The development of cheaper and more effective anthelmintics, molluscicides, pesticides and insecticides will make the undertaking of mass control programmes possible, Furthermore, the development of simple but specific serological and other dianostic tests will help not only in epidemiological investigation but also in control of the various infect2ons. Abdussalam, M. (1951;). Proc. X. Pak,Sci.Conf., 2, 11 (~enrlnt).

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