Animal Parasites and Human Diseases

380 ANIMALS AND DISEASE ANIMAL PARASITES AND HUMAN DISEASES By Paul C. Beaver, Ph.D. Department of Tropical Medicine and Public Health, Tulane University School of Medicine P A1IASITES fall only roughly into the two directed to parasitic infections caused by categories implied in the title of this worms which, regardless of length of resi- discussion. While a few of them arc totally dence in the human body, do not reach full dependent upon htmman hosts, and some are reproductive maturity and are therefore not able to develop only in other animals, a diagnosable by the usual laboratory majority of the parasites commonly re- methods. It is of course the larval stages ferred to as “parasites of man” are in or immature adults that arc involve(! amid!, reality parasites of other animals.1 In the owing to their tendency to be mostly in the latter grouip are such familiar examples as tissues and in many instances difficult to Trichinella, found in rats and many other find and identify, the infections caused by animals, including pigs; Balantidium and them are often unrecognized. Largely for some lesser protozoa of pigs; Toxoplasma, this reason the frequency and severity of which occurs in many wild and domesti- infections of this nature have not been cated animals. Trypanosoma cnuzi, which is fully determined. There are, however, some carried by a variety of animals, is the cause familiar examples. of Chagas’ disease commonly seen in parts Certain well known larval tapeworm in- of South America and found recently in a fections are acquired from other animals. child in Texas.2 Other examples include Examples are echinococcus (hydatid) and Isospora of undetermined hosts, possibly in- coenunuis whose infective stages are carried cluding the dog; Trichostrongylus species in the feces of dogs, and sparganuim which that commonly are found in sheep and comes from infected cats and (logs hut ne- goats; the small tapeworms, Hymenolepis quines development in aquatic hosts before nana and Hmcnolepis diminuta, of rats it is infective for man. These infections arc and mice; and! the common dog tapeworm, uncommon in the United States and are Dipylidium caninum. There arc others especially rare in children. whose endemicity in any area depends It is sometimes stated! that the comiimon somewhat on the presence of suitable non- ascarids and whipworms of children human hosts, and still others that are able (Ascanis lumbnicoides and Tnichuiris tn- to reach maturity in man but are rarely chiura) are identical with those of pigs. It involved in medical problems because in- has not been satisfactorily demonstrated fection is acquired only by eating uncooked that they are cross-infective to the extent earthworms and insects. It might be men- of reaching full maturity in the reciprocal tioned, as a matter of interest, that occa- hosts, but it can be safely assumed that siona!ly other animals may acquire pana- when children swallow the infective eggs sitic diseases from their human associates, of pig ascaris, the larvae invade the liver as for example dysentery and diarrhea in and the lungs even if they fail to reach ma- dogs, caused by Entamoeba histolytica and tumrity in the intestine. Strongyloides sterconalis. Creeping eruption, or cutaneous larva In all of the above mentioned parasitic migrans, has been recognized for many infections, diagnosis is usually based on con- years as due to larval stages of the dog and ventional laboratory methods, and both cat hookworm, Ancylostoma brazihiense. It clinical and laboratory workers are gen- is not always appreciated, however, that erally familiar with the problems presented other species of ncmatode larvae also pro- by them. Iii recent ‘ears attention has been ducc creeping eruption, and that after a ADDRESS: New Orleans, Louisiana. Downloaded from www.aappublications.org/news by guest on October 1, 2021 AMERICAN ACADEMY OF PEDIATRICS - PROCEEDINGS 381 period of migration in the outer layers of other indications of infection gradually the skin some of the larvae move into disappear. Conclusive diagnosis can be deeper tissues, including the lungs.3 made only by direct demonstration of larvae Among those infections acquired through in liver tissue or in other tissues post contact with dogs and cats in the United mortem. Usually a satisfactory diagnosis States, it is believed that visceral larva mi- can be made on clinical grounds, especially grans, caused by ascarids of dogs, is proba- if supported by senodiagnostic tests pres- l)lV the most widespread and most damag- ently being developcd.#{176}2 imig to children. Although this infection Toxocara is the only larval nematode yet )rolmbly has been common among tOddler- identified in the tissues of children with age children for many years, it was not visceral larva migrans. It is anticipated, recognized amid described until 1952. however, that others will he discovered. It During the past 5 years much has been was mentioned earlier that dog and cat written about visceral larva migrans and hookworm larvae that cause creeping erup- case reports, including some fatalities, have tion also invade the deeper tissues. Their appeare! abundantly in pediatric jour- behavior in experimental animals suggests nals. s It will therefore suffice merely to that several species of hookworms not review 5OC of its main features. The para- ordinarily infesting man probably behave site, Toxocara, is a large roundworm which somewhat like Toxocara in humans and in its appearance amid life cycle resembles may therefore produce the visceral larva Ascaris lumbricoidles, the commiion large migrans type of disease. Studies by Nichols roundworm of children. The dog and the have made it possible to identify some of cat each comiimm)nly harbors a species of its these larvae either after isolation from fresh own, T. canis amid T cati, respectively. Eggs tissues or in stained sections.33’ ‘ Two of eliminated iii the aninials’ feces are not in- the Toxocara larvae recently identified in fective when passed but after 2 or 3 weeks our laboratory arc noteworthy. One (to be iii warm, dLIni1), shaded soil each egg, of reported from California by Dr. A. R. which there may be hundreds in 1 or 2 gm Irvine) was the first to be found in the eye of soil, comitains an infective larva capable since Wilder reported a series of sumch cases of prodtmcing a new mature infection in a in 1950;15 and the other (reported a few natural host, or a long-lasting larval infec- months ago from Washington, D.C. by tion in a child. When infective eggs are in- Bruton and Jaffurs16) was the first to be gested I)y children, the larvae erupt from found in a needle biopsy. the egg, migrate to the liver, and from there Biopsies of the liver for diagnosis of to other parts of the body including the cen- suispected cases of visceral larva migrans tral nervous system and the eye. Destructive have revealed three infections of Capillania eosinophi!ic granulomatous lesions are hepatica in children-one each in Balti- formed! aroundi the minute worms or along more,17 Hawaii’8 and Souith Afnica.19 Nec- their migratory paths through the tissues. ropsy examination earlier had brought to Marked eosinophilia of the blood, hypcr- light only three such cases, one of which globuhinemia and enlargement of the liver was in a child in New Orleans.2#{176} This are characteristically noted!, along with worm’s natural location is in the liver of variable symptoms including fever, cough, rats and other small rodents, and it has the loss of appetite, irritability and neumnologic peculiar trait of putting its eggs in the (histurbamices. Threatening lesions in the tissues where they can not be eliminated eve bearing a superficial resemblance to from the body. Capillania has not been ade- retimioblastoma have occurred in a number quately stu(lied but it appears probable that of instances. Larvae Persist alive in the human imifection is acquired! through the in- tissues for many months, dumning which time gcstion of soil contaminated by animals the eosinophilia may remain high while the whose feces bear the eggs digested from the Downloaded from www.aappublications.org/news by guest on October 1, 2021 :382 ANIMALS AND DISEASE liver of infected rats. Like Toxocara, the about the frequency and clinical importance eggs must undergo development outside the of infection with immature stages of this host before they are infective. Clinically, common parasite. Indeed its possible role in Capillania infection can not be distinguished dyscntenies of unknown cause in children from visceral larva migrans caused by has already been considered by the speaker, Toxocara. Although it appears to be an as it must also have by others. There arc uncommon infection in children it seems doubtless still some important parasitic dis- to be especially damaging since only one eases unidentified. Some of them may fill individual infected vith Capillaria is the gaps among the diseases of unknown on known to have survived, and even in this doubtful etiology, such as tropical eosino- case the child had not entirely recovered philia which, according to some prelimi- when the report was made.19 On the other nary reports, appears to be a non-patent hand, its real prevalence is unknown and ncmatode infection related to visceral larva it is possible that some clinically significant 627 but non-fatal infections arc being over- Since the nonpatent, cryptic parasitic looked. infections, especially the filth-borne, soil- One other type of zoonotic infection generated ones, are more common in chil- should be mentioned. In 1941 a worm dren than in adults, it is expected that new resembling the hcartworm of dogs (Dino- knowledge of these infections will come filaria) was discovered in the inferior vena from pediatricians who look for them.

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