Bull Pan Am Health Organ 14(3), 1980.

SCHISTOSOMIASIS AND ITS INTERMEDIATE HOSTS IN THE LESSER ANTILLEAN ISLANDS OF THE CARIBBEAN

M. A. Prentice1

Schtitosomiasis poses a significant health threat in the Caribbean area. This article reviews the status of the disease and various fac- tors contributing to its transmission on the islands of the Lesser An- tilles.

Introduction showed signs of resistance to infection. Because the collections came from widely The discontinuous distribution of Schisto- separated locations, the Sturrocks suggested soma mansoni in the Caribbean islands results that all Caribbean strains of B. gkzbrata and from accidents of history, geography, and the S. mansoni were likely to be mutually com- migration of both infected people and inter- patible, and they concluded that the only bar- mediate host snails. The spread of infection riers to the spread of schistosomiasis were requires the presence of infected people, a physical. susceptible snail host, poor sanitation, and The author visited St. Kitts, Montserrat, human dependence upon snail-infested Antigua, Dominica, and Grenada in late water. The various Caribbean countries differ 1977 and early 1978, as well as St. Maarten in in these regards, and the relationships be- early 1979. This paper reviews the history and tween the various critical factors determine current status of schistosomiasis transmission whether and to what extent the disease exists. in these and other islands of the Lesser An- Sturrock and Sturrock (I) cite reports of tilles (see Figure 1). transmission in the following places: the Dominican Republic, Puerto Rico, Vieques, Islands with a History of Schistosomiasis St. Maarten, St. Kitts, Montserrat, Antigua, Guadeloupe, Martinique, and Saint Lucia in St. Maarten (120 Km2) the Caribbean and Venezuela and Suriname on the South American mainland. Ferguson This small island is well-drained and et al. (2,3) report that the infection has been nowadays chronically short of water. There eliminated from St. Kitts and Vieques. Of the are no perennial streams, and domestic water remaining places, Trinidad, Grenada, Bar- comes from wells and a desalination plant. bados, and St. Vincent are apparently free of Jones (4) reported seeing 24 cases of in- Biomphalariu glubrata (the most important testinal schistosomiasis from St. Maarten be- snail host in the area), although B. straminea tween 1920 and 1922, some of them serious. is present in Trinidad and Grenada. Nearly all came from Colombier, a village in Sturrock and Sturrock (I) showed that B. the hills where there was a sugar mill. Hoff- glubrata from Dominica, the Dominican man (5) reported that standing water and Republic, Puerto Rico, and French Guiana schistosomiasis were still present there in were susceptible to St. Lucian S. mansoni, 1929. However, no recent cases of the disease although the snails from French Guiana have been reported (6). There are no longer any snail habitats at Colombier, the wettest valley in St. Maarten, ‘Biologist and staff member of the Rockefeller Foun- dation; Research and Control Department. P.O. Box 93, and surface water remains only a few days Castries, Saint Lucia. following heavy rain. The local people

258 Prentice l SCHISTOSOMIASIS IN THE LESSER ANTILLES 259

3 OSt. Maarten

jt.Kitts fi Antigua

Montserrat 0

Guadeloupe t+

Dominica 0

Martinique Q

St. Lucia 0 Biomphularia glabrutu, intermediate host of St. Vincent Barbados schistosomiasis in the Caribbean. The swelling at 0 b the base of the right tentacle is a primary . # sporocyst of S. munsoni. Photo by the author. W 0 M . 0 m Grenada ridge with well-drained and fertile lower D E slopes supporting sugar-cane cultivation. a Rainfall is moderate and surface water is 0 severely limited below the forest line. Schistosomiasis was previously hyperen- 100km demic in Boyd’s Village and several other coastal villages bordering streams. In 1932 T Brzad Jones (7) reported an island-wide schistosomi- asis prevalence of nearly 25 per cent based on single saline fecal smears. The infection dis- appeared in the 1940s when streams running Figure 1. The Lesser Antilles. off the central mountain range were progres- sively tapped for water. Ferguson et al. (2) associate this general change with the exten- reported that by 1945 only one of the six sive deforestation that took place in the first “permanent” rivers on the island continuously half of the century; and Dr. Gibbs, who was reached the sea, the rest flowing only during born in the area, comments that the wet the rains when snail populations were unable season is no longer as well-defined or as wet as to establish themselves. it used to be. By 1959, B. glubrata was confined to an area called the West Farm Gut, and stools St. Chrzitopher (St. Kitts; 186 Km2) from 188 randomly selected schoolchildren and villagers were negative for S. mansoni (2). St. Kitts is a small elongated island Since then, attempts have been made to characterized by a forested central mountain eliminate B. glabruta from the island by using 260 PAHO BULLETIN . vol. 14, no. 3, 1980 molluscicides and the competitor snail Marisa village adjoining the main water-collecting cornuarietis. After Bayluscide treatments in area. fie also notes that planorbid snails were 1965, B. glabrata appeared to be absent from abundant in the pools and sluggish streams, the island until it was observed again in West and reports that a bifid-tailed cercaria from a Farm Gut in 1975. In 1976 Ferguson (8) planorbid snail was obtained from the filter reported finding the snail for the first time in bed of the St. John’s city water supply. Fountains River. Bayluscide was applied in Annual medical reports mention Bendal’s 1976, but the application was restricted to the Stream and the Body Pond complex, a series stretch of river below the last of several of dammed pools (originally the only reservoir domestic water intakes and so was ineffective. for the St. John’s water supply) as being areas A September 1977 visit did not reveal any of high transmission in the past. B. glabrata in West Farm Gut, and Mar&a Because of water impoundment projects, was abundant; however, this situation has there are no longer permanently flowing been observed before and the Biomphalaria streams on the island, and the disease has have recovered. The B. glabrata colony in declined. The last reported cases occurred in Fountains River was thriving. Nevertheless, the area of Sweets and Liberta villages about B. glabrata is now so restricted in its distribu- 13 years ago; these cases were asymptomatic tion that transmission of S. mansoni is un- and were discovered by routine parasitologic likely to recur. Both the West Farm Gut and examinations (10). Fountains River habitats are relatively A 1977 survey showed B. glabrata to be isolated, the former being protected as a widespread and abundant in pools and dams water supply catchment area and the latter throughout the island. Many of the new reser- being mostly at an altitude of 450 meters in voirs are infested, but human contact with dense gallery forest. The infection (probably them is limited. It is possible that low-grade a zooanthroponosis) once reported by Came- transmission continues in the Body Pond area ron (9) in resident West African green among youths fishing the ponds, but in- monkeys (Cercopithecus sabaeus) is presumed creased transmission is unlikely unless the to have died out, since no infections have large reservoirs now under construction been found in Biomphalaria for many years. become important recreation sites. A single empty shell of the melaniid snail Antigua (278 Km”) Thiara granifera (also known as Tarebia granzyera) was recently collected from the new This comparatively flat island is generally Collins Dam. Wading birds are common in well-drained: snail habitats have been Antigua, and there is every likelihood that restricted to the few permanently flowing this snail will spread rapidly, as it has recently streams and the many existing reservoirs and in Puerto Rico, Grenada, and Dominica. If it ponds. Cases of intestinal schistosomiasis were does spread, it may exert a further restraining common early in the century, and in fact S. influence on the population of B. glabrata. mansoni was first differentiated from S. haematobium in 1907 when Sir Patrick Man- Montserrat (181 Km2) son described lateral-spined eggs found in the stool of a patient who had worked on Antigua This small, hilly island has many habitats and St. Kitts. suitable for B. glabrata. Jones (7), writing in According to the 1923 Annual Report of 1932, mentions the presence of planorbid the Medical Department, a hookworm survey snails and also refers to cases of schistoso- detected S. mansoni in 18 per cent of those miasis imported into St. Kitts from Montser- examined in St. John’s parish, and Jones (7) rat. It is possible therefore that the infection tells of a reported 60 per cent prevalence in a has been present on Montserrat for many Prentice 9 SCHISTOSOMIASIS IN THE LESSER ANTILLES 261

years, although it has apparently not been in the days when water power was important. sufficiently serious to draw attention. About Stool examinations have revealed a schistoso- 10 years ago the Hospital for Tropical miasis prevalence of 24 per cent over a Diseases in London diagnosed intestinal schis- fourteen-year period at St. Claude on Basse- tosomiasis in a Canadian youth who had Terre, with a recent increase to 43 per cent bathed in Farms River but had reported no among 15,407 people examined in 1972. other contact with water in endemic areas. B. glabrata is widespread on both islands More recently, another case was diagnosed in but is most numerous on Basse-Terre. B. a native of Montserrat living near Barzey’s schrammi also occurs but is refractory to in- Stream, several miles away over a mountain fection with S. mansoni. ridge from Farms River (II). Combes et al. (13) have reported Rattus In 1977 a brief survey of the island showed rattus and Rattus norvegicus naturally in- that B. glabrata was present in both Barzey’s fected with S. mansoni in an uninhabited lake Stream and Farms River. The survey took area, but Theron et al. (14) have concluded place shortly after a period of heavy rain that that rats are not an important factor in areas could have been expected to flush many snails where human transmission occurs. from these streams. The survey results thus suggest that large snail populations exist in Martinique (1,000 KmZ) these streams during the dry season. B. gla- brata could not be found in the Belham This volcanic island is topographically River, although habitats were plentiful and similar to Grenada, Saint Lucia, and Do- associated snails (Physa, Potamopyrgus) were minica-except in its southern portions, abundant. where it is less mountainous than the others. Many youths from Harris’ Village regularly Rainfall is high, and snail habitats are swim in a pool below a derelict dam wall in widespread in natural streams and ditches the Farms River, and there is evidence that constructed for irrigation and drainage. people wash and bathe in Barzey’s Stream. It Schistosomiasis was first reported in 1906. seems likely that a survey of local residents Gretillat (15) quotes a report by Leger, who would reveal evidence of low-grade transmis- found an 8.5 per cent prevalence among sion associated with both rivers. troops in 1908, and Not (16) found 32 of 45 children in an orphanage infected. Guyard Guadeloupe (1,513 Km2) and Pointier (I 7) reported a prevalence of 6.4 per cent for Martinique as a whole, while Guadeloupe consists of two islands that are Mathieu (18) reported a 70 per cent separated by a narrow strait and linked by a prevalence in the Commune of Lorrain. As bridge. The western island, Basse-Terre, is yet no control measures have been under- mountainous, forested, and contains numer- taken. ous permanent rivers, while the eastern island The snail situation is somewhat confused. is low-lying, well-drained, and has only tem- B. glabrata is apparently rare. The snail was porary streams. Schistosomiasis is most first reported by Bordaz (19); its location (in a prevalent on Basse-Terre. pond at the botanical gardens) suggests in- These islands have recently been studied troduction by a human agency. Dreyfuss (20) extensively in preparation for introducing and Gretillat (15) reported finding it at many schistosomiasis control measures. Golvan et sites around Fort-de-France, but Guyard and al. (12) report that the infection has become Pointier (17) believed that it may have been important relatively recently, owing to in- confused with Helisoma or with large speci- creased irrigation and the domestic use of mens of B. straminea, since they were able to previously neglected canals and flumes built collect glabrata from only four sites in the six 262 PAHO BULLETIN l vol. 14, no. 3, 1980

years 1972-1978. In 1972 infected snails were streams. Snail habitats are plentiful wherever obtained from one of four collecting sites - a the forest has been cleared for agriculture. reservoir whose snail population had been Although schistosomiasis may have been pres- previously determined (probably erroneously) ent at a low level much earlier, it was first as Australorbis peregrina by Gretillat (15). reported by Vinter (23) in the Soufriere The most common planorbid is B. strami- Valley in 1925. It is possible that the infec- nea (21). This snail is an important host in tion’s prevalence was then increasing, since parts of Brazil, and Paraense (22) reports there is no record of S. mansoni eggs having finding it naturally infected in Martinique. been found in 100,000 stool examinations However, the relative importance of B. done during a Rockefeller Foundation hook- glabrata and B. straminea in transmission is worm control campaign mounted between far from clear. 1914 and 1924. By the 197Os, before control In addition, Guyard and Pointier (I 7) have started, the schistosomiasis prevalence was reported B. schrammi at Fort-de-France. above 70 per cent in the most involved com- This snail is not susceptible to infection with munities. S. mansoni. Also, B. hawanensis was reported B. glabrata is widespread and is the only by GrCtillat (15), but this may have been due Biomphalaria species recorded in Saint to misidentification of B. straminea, which Lucia. Sturrock (24) discusses the transmis- Guyard and Pointier (I 7) have reported as be- sion pattern in Cul-de-sac Valley and shows ing common in the area concerned. that the most important sites are the streams where snails from high-level marshes can Saint Lucia (614 Km2) establish themselves during the dry season. This snail distribution pattern, which I have Saint Lucia is a rugged, forested island found in other valleys, is typical of moun- with heavy rainfall and many permanent tainous areas with heavy rainfall. The ecology

An alluvial valley in Saint Lucia. Transmission of schistosomiasis may occur in the river and its tributaries during the dry season when conditions are suitable for a build-up of B. glabruta colonies. Photo by the author. Prentice 9 SCHISTOSOMIASIS IN THE LESSER ANTILLES 263 of fresh-water habitats in relation to their col- and had spread into a second stream system onization by B. glabrata has been described near Trafalgar. However, the original Trafal- by Sturrock (25), and the results of snail con- gar habitat was heavily infested with T. trol in Cul-de-sac Valley have been reported granifera, and no B. glabsata were collected. by Sturrock et al. (26). Jordan (27) has re- T. granzfera was not observed during the viewed the progress of snail control, the provi- 1974 survey, and it seems to have been in- sion of water supplies, and chemotherapy, the troduced into Dominica very recently. It is three basic schistosomiasis control methods now ubiquitous in the Roseau Valley. Fergu- employed in Saint Lucia. son (8) has commented on the high densities As a result of the control program now in achieved by this snail and has suggested that progress, the prevalence of schistosomiasis has it must exert a “sustained restrictive pressure been substantially reduced, and the threat of upon all other snails in a habitat.” Saint Lucia residents carrying the infection to There have been no reports of autoch- other areas has diminished. However, the pos- thonous schistosomiasis cases on Dominica, sibility remains that snails from Saint Lucia although the potential for transmission cer- could be transported to St. Vincent or tainly exists at Wotten Waven and infected Grenada, since extensive snail control is not people live on the neighboring islands of part of the Saint Lucia program. Guadeloupe and Martinique. Although B. glabrata is spreading slowly throughout the Islands without a History of Schistosomiasis Roseau Valley, it is currently absent from the most dangerous habitat at Trafalgar. While Dominica (745 Km2) this may be only a temporary setback, it is possible that the faster-spreading T. granzfera This extremely mountainous island sup- may slow down or even prevent B. glabrata ports dense forest, and heavy rainfall creates from colonizing the island’s rather limited numerous torrential streams. It has appar- number of suitable habitats. ently only recently been invaded by B. glabrata. In 1964 the Smithsonian Institute St. Vincent (387 Km2) Biological Survey first reported the snail in ar- tificial ponds in and around Roseau, the This mountainous forested island, de- capital. Despite attempts to eradicate these scribed by Harrison and Rankin (29), has a populations, the snail spread via fish-culture heavy rainfall and is similar to Saint ponds; by 1972 it had reached a natural pond Lucia-although the highest parts have been situated high in the Roseau Valley and was modified by more recent volcanism. Its fresh- common in ornamental ponds at a nearby ho- water habitats, fauna, and water chemis- tel. Further attempts to eradicate the snail us- try-which resemble those of Saint Lucia- ing Bayluscide succeeded only in destroying have been described (29-31). the hotel pool colony (28). Schistosomiasis does not occur on St. Vin- A 1974 survey showed that B. glabrata was cent because Biomphalaria spp. are absent, still present in the natural pond and had although suitable habitats abound and asso- spread into a large seepage area near a small ciated snails are present. If B. glabrata were community at Wotten Waven. It was also introduced from nearby Saint Lucia, it might found in a stream and marsh system among colonize the islands; and because St. Vincent houses at Trafalgar, over a mile away on the is more densely populated, schistosomiasis opposite side of the precipitous Roseau might thrive. Although the transmission Valley. potential is high, however, the risk of in- A more recent 1978 survey showed that the troducing the infection is diminishing rapidly snail was firmly established at Wotten Waven due to the control effort on Saint Lucia. 264 PAHO BULLETIN l vol. 14, no. 3, 1980

Barbados (428 Km2) soni. Adults of the most recent collection from Grenada once again proved insuscepti- This flat coral island is generally well- ble to St. Lucian S. mansoni, but one patent drained and has few snail habitats. Fresh infection occurred among 107 survivors of 407 water is stored naturally underground rather laboratory-reared juvenile snails exposed to than in surface pools. There have been no approximately 1 miracidium each. This ex- reports of autochthonous cases of schistoso- tremely low susceptibility is unlikely to sup- miasis. port natural transmission under conditions B. helophila has been collected (32) by prevailing on Grenada. Paraense, but it is a poor host, and both the Although B. straminea is known to occur in risk and the transmission potential involved several localities (and a prolonged search are very low. would doubtless reveal it in many more) it is absent or infrequent in many suitable habi- Grenada (310 Km21 tats dominated by T. granifera. This latter snail was first reported on Grenada in 1970 by Grenada is the most southerly of the Lesser Ferguson (8). It is now widespread and in Antilles. It is a small, mountainous, forested several places its numbers exceed 500 indi- island with heavy rainfall and numerous per- viduals per square meter. manent streams and rivers. Neither B. gla- brata nor autochthonous cases of schistoso- Discussion miasis have been reported, but B. straminea is apparently widespread. Malek (33) col- Biomphalaria species are discontinuously lected planorbids, which he referred to as B. distributed throughout the Caribbean region. havanensis, from three widely separated Table 1 shows the members of the genus re- localities in 1965; adult snails from this collec- ported from each island in the Lesser Antilles tion proved insusceptible to S. mansoni from and indicates whether the ranges of those both Puerto Rico and Saint Lucia. Richards species within each island are widespread or (34) reported collecting a planorbid, de- restricted. scribed as B. straminea, from two sites in There is ample evidence that gastropods or 1971. Again, adult snails proved insuscepti- their egg clusters can be transported by an- ble; but a very few laboratory-reared juvenile imals and birds in mud and detritus and by snails yielded patent infections. man in shipments of aquatic vegetation (35, During a visit of mine in January 1978, personal observations). The introduction of planorbids were collected from a stream at T. granifera into Puerto Rico (around 195’3), Moya and a roadside ditch at Tivoli on the Grenada (perhaps around 1970), Antigua eastern side of the island. These snails were (date unknown), and Dominica (between identified by Professor W. L. Paraense as B. 1973 and 1977) from its original point of in- straminea. However, in 1978 planorbid snails troduction to the Western Hemisphere in were absent from the sites of Malek’s 1965 col- Florida (8, personal observations) dem- lection, and so it was not possible to deter- onstrates that the sea is no barrier, and the re- mine whether both B. havanensis and B. cent introduction of B. glabrata into straminea were still present or whether the Dominica (albeit probably by human agency) specimens collected earlier were B. strami- confirms this. nea. The distribution of Biomphalaria species in B. straminea is an important intermediate the Caribbean is therefore best explained by a host in parts of Brazil, where its extreme vigor combination of land movement and snail and high density compensate for its low sus- dispersion, the latter process being ac- ceptibility to the Brazilian strain of S. man- celerated by human intervention. There is Prentice . SCHISTOSOMIASIS IN THE LESSER ANTILLES 265

Table 1. Reported distribution of Biom~hualaria species and Thiara granifera in the Lesser Antilles.

Distribution Presence of Biomphalak status as of reported Thiara species intermediate Biomphalarzk granifera Island reported host species reported

St. Kitts B. glabrata Yes restricted, declining Montserrat B. glabrata Yes widespread Antigua 3. glabrata Yes widespread yes (1977) Guadeloupe B. glabrata yes widespread B. schrammi no restricted Dominica B. glabraata yes restricted, yes (1977) spreading Martinique B. glabrata yes very restricted B. straminea possibly widespread B. schrammi no very restricted B. helophila* ? B. peregrina’ I B. havanensis* ? Saint Lucia B. glabrata yes widespread yes (1978) Barbados B. helophila poor restricted yes (1969) St. Vincent none Grenada B. straminea possibly restricted yes (1970) B. havanensis*

*Identification suspected of possible inaccuracy. thus every likelihood that B. glabrata will the lung flukes Paragonimw westermanni eventually be transported to both St. Vincent and P. kellicotti. However, man only con- and Grenada. Whether it subsequently be- tracts paragonimiasis incidentally by eating comes established there will depend on local the second intermediate host (various species factors-including, on Grenada, the possibil- of fresh-water crustaceans) in the raw state. ity of strong competition from already- This is unlikely to become a problem in the established planorbid and other aquatic Caribbean, where river shrimps are always snails. well-cooked before consumption. The recent introduction of the ovovivip- Tables 2 and 3 provide an overview of the arous and parthenogenetic snail T. granzyera present situation on the Lesser Antilles; and into the region will almost certainly have a Table 3 assesses the risk that schistosomiasis restraining effect on planorbid snail popula- could be introduced and spread on islands tions in the future. Ferguson (8) reports in- with no past history of the disease. Of these stances of declining B. glabrata populations latter islands, Dominica must be considered in areas invaded by T. granzyera in Puerto at greatest risk, since a good host snail is Rico. In Grenada enormous numbers of T. already established in areas where human granzyera were present in torrential streams, contact occurs, and there is a nearby source of demonstrating a clear ability to withstand infected people. However, the transmission heavy flushes. The snail may therefore prove potential there is relatively low, due to the a particularly effective tool for control efforts very high gradient of most streams. on mountainous islands such as Saint Lucia, On islands where B. glabrata is absent, Dominica, Martinique, and Guadeloupe. every effort should be made to keep it so. A T. granzyera is the first intermediate host of likely- and preventable-way of importing 266 PAHO BULLETIN l vol. 14, no. 3, 1980

Table 2. Overview of the present schistosomiasis situation on islands with a history of the infection.

Island’s Relative relative degree susceptibility of human to the Relative contact indicated extent with Trans- Risk of Status snail host(s) of snail infected People mission increasing Island of the disease present habitats water per km2 potential disease

St. Maarten Has died out none none - 166 none none (deforestation) St. Kitts Died out in 1946 B. glabrata \ f + (?I 300 very low very low (water management) c+ + +I Antigua May have died out B. glabrata + + 170 low low (water management) c+ + +I Montserrat + B. glabrata if +++ 140 moderate moderate (May be increasing) c+ + +) Guadeloupe +++ B. glabrata +++ +++ 225 high high t+++j Martinique +++ B. glabrata fff +++ 320 high high t+ + +) B. straminea (+) Saint Lucia + B. gla brata +++ +++ 210 high uncertain Declining (control) t+ + +)

Table 3. Overview of the schistosomiasis risk on islands with no history of the infection.

Island’s Potential relative degree susceptibility of human Risk of to the Existence of contact with People disease indicated appropriate infected Transmission intro- Island snail host snail hosts water s potential duction

Dominica 8. glabrata if ++ 105 moderate very high c+ + +) St. Vincent none ii+ +++ 285 high if B. glabrata high became established Barbados B. helophila + + 615 IOW low (f) Grenada B. slraminea +++ ++ 355 high if B. glabrata low (+I became established

juvenile snails and egg masses is upon aquatic periodically examine the snail fauna in public plants imported for ornamental or pisci- and private ponds. cultural purposes. Some islands already ban It is more difficult to see what can usefully the importation of such plants, but such laws be done on islands like Dominica, where the are difficult to enforce because fishermen intermediate host is already present. It is im- with small boats make many unregulated pas- practical to eradicate the snail or to screen sages. Therefore, in all cases it would be visitors for schistosomiasis. So whether an in- desirable to have a qualified malacologist fected visitor will contaminate the snail- Prentice l SCHISTOSOMIASIS IN THE LESSER ANTILLES 267

infested areas-before improvements in the Throughout the infected world, in the ab- general level of hygiene make that un- sence of controlling factors, schistosomiasis likely-remains a matter of chance. transmission has increased as population den- On islands where the disease is hypo- sities have increased. Since there is no reason endemic or suspected, and where there is a to suppose that the Caribbean is immune danger of increased prevalence (e.g., on from this trend, it is important that efforts be Montserrat), every effort should be made to made now to stop the spread of the disease. detect cases and treat them.

ACKNOWLEDGMENTS

I would like to thank all those officials Professor W. L. Paraense for identifying col- whose courtesy and cooperation made my vis- lected snails and Dr. P. Jordan for his helpful its to the islands possible. I also wish to thank advice.

SUMMARY

This article reviews the history, present status, serious risk because infected people live on nearby and potential for spread of intestinal schistoso- islands. The potential for transmission is high on miasis in the Lesser Antilles in the light of factors both Grenada and St. Vincent, but Grenada lacks which contribute to its transmission. a good snail host and no Eiornphalaria species at all Among the islands with a previous history of the have been found on St. Vincent. Barbados is too disease, St. Maarten is no longer affected due to well-drained for snail hosts to thrive. reduced rainfall. On St. Christopher and Antigua Overall, despite the recent rapid spread of the transmission became nonexistent or very slight competing melaniid snail Thiara grunz@era, there is after many snail habitats were destroyed by water a very real danger of 8. glabrata reaching management programs. On Saint Lucia the infec- uninfected islands. Also, around the world schis- tion is under control. On Montserrat the tosomiasis transmission has tended to increase with prevalence of schistosomiasis is low but may in- rising population density, and there is no reason to crease. On Guadeloupe and Martinique the think that the Caribbean area is immune to this prevalence of endemic infection is increasing. trend. It is therefore important that steps be taken Of the islands with no history of the disease, now to stop the spread of the disease. Dominica is being invaded by B. gla brata and is at

REFERENCES

(I) Sturrock, R. F., and B. M. Sturrock. Obser- (4) Jones, S. B. Some notes on intestinal bilhar- vations on the susceptibility to Schtitosoma mun- ziasis in the West Indies. J Trap Med 25:25-27, soni from St. Lucia of several Caribbean strains of 1922. snails of the genus Biomphularzk. West Indian Med (5) Hoffman, W. A. From San Juan to Aruba. P J 19:9-13, 1970. R J Pub Hlth Trap Med 5:357-369, 1929. (2) Ferguson, F. F., C. S. Richards, S. T. (6) Gibbs, V. Chef de Medecin, Marigot Hos- Sebastian, and I. C. Buchanan. Natural abate- pital, St. Maarten; personal communication, 1979. ment of Schtitosoma mansoni in St. Kites, British (7) Jones, S. B. Intestinal bilharziasis in St. West Indies. Public Health 74:261-265, 1960. Kitts, British West Indies. J Trap Med 35:129-136, (3) Ferguson, F. F., J. R. Palmer, and W. R. 1932. Jobin. Control of schistosomiasis on Vieques Is- (8) Ferguson, F. F. The role of biological agents land, Puerto Rico. Am J Trap Med 17:858-863, in the control of schistosome bearing snails. At- 1968. lanta, U.S. Department of Health, Education and 268 b PAHO BULLETIN l vol. 14, no. 3, 1980

Welfare, 1977, p, 37. Americas. Brazil Med ll:ll-14, 1975. (9) Cameron, T. W. M. Observations on a (23) Vinter, N. S. B. Schistosomiasis in St. parasitological tour of the Lesser Antilles. Proc R Lucia. ET MedJ, 11 January 1964, p. 119. Sot Med 22:37-45, 1929. (24) Sturrock, R. F. Field studies on the (10) Boyd, A. I., Chief Medical Officer, An- transmission of Schistosoma mansoni and on the tigua; personal communication, 1977. bionomics of its intermediate host, Biomphalariu (II) Wooding, C. D., Chief Medical Officer, glabrata, on St. Lucia, West Indies. Int J Parasitot Montserrat; personal communication, 1977. 3:175-194, 1973. (12) Golvan, Y. J., R. Houin, C. Combes, M. (25) Sturrock, R. F. Ecological notes on habitats Deniau, and F. Lancastre. Transmission naturelle of the freshwater snail Biomphalaria glabrata, in- de la Bilharziose a Schistosoma mansoni en termediate host of Schistosoma mansoni on St. Guadeloupe (Antilles francaises). Ann Parasit Lucia, West Indies. Carib J Sci 14:149-161. 1974. Hum Corn@ 52:259-275, 1977. (26) Sturrock, R. F., G. Barnish, and E. S. (13) Combes, C., N. Legar, and Y. J. Golvan. Upatham. Snail findings from an experimental Rats et Bilharziose en Guadeloupe. Acta Trap mollusciciding programme to control Schistosoma 32:304-308, 1975. mansoni transmission on St. Lucia. Carib J Sci (14) Theron, A., J. P. Pointier, and C. Combes. 4:231-240, 1974. Approche ecologique du problems de la respon- (27) Jordan, P. Schistosomiasis: research to con- sibilite de l’homme et du rat dans le fonctionne- trol. Am J Trap Med Hyg 26:877-886, 1977. ment dun site de transmission a Schistosoma man- (28) Sturrock, R. F., personal communication. soni en Guadeloupe. Ann Parasit Hum Comp (29) Harrison, A. D., and J. J. Rankin. Forest 53:223-234, 1978. litter and stream fauna on a tropical island, St. (15) Gretillat, S. Prospection malacologique aux Vincent, West Indies. Verb Internut Verin Limnol Antilles francaises. Observation sur l’ecologie et 19:1736-1745, 1975. l’elevage au laboratoire de ,Lymnaea cubensis. Rev (30) Harrison, A. D., and J. J. Rankin. Eleu Med Veter Pays Trap 2:279-289, 1967. Hydrobiological studies of Eastern Lesser Antillean (16) Not, F. La bilharziose a la Martinique. Islands, I. St. Vincent: Freshwater habitats and Bull Sot Path Exot 3:26, 1910. water chemistry. Arch Hydrobiol 5O(Suppl.): (17) Guyard, A., and J, P. Pointier. Faune 96-144, 1976. malacologique dulcaquicole et vecteurs de la (31) Harrison, A. D., and J. J. Rankin. schistosome en Martinique (Antilles francaises). Hydrobiological studies of Eastern Lesser Antillean Ann Parasit Hum Camp (in press). Islands, II. St. Vincent: Freshwater fauna-its (18) Mathieu, J. M. Resultants obtenus a la suite distribution, tropical river zonation and bio- dune enquete immuno-epidemiologique sur la geography. Arch Hydrobiol50(2,3):275-311, 1976. bilharziose a la Martinique. Doctoral thesis No. 57, (32) Schistosomiasis Snail Identification Center Universite de Bordeaux, 1972. for the Americas. Annual Report to the Pan (19) Bordaz, G. Liste des coquilles recueillies a American Health Organization, 1967. la Martinique. Bull Sot Hist Nat Autun 12:5-24, (33) Malek, E. A. Biomphaluria havanensis 1899. (Pfeiffer) from Grenada, West Indies. Nautilus (20) Dreyfuss, R. Les planorbes de la Marti- 89:17-20, 1975. nique. Bull Sot Fr Hist Nat Ant 2:41-45, 1953. (34) Richards, C. S. A potential intermediate (21) Paraense, W. L. In: A. S. Cunka (ed.). Es- host of Schistosoma munsoni in Grenada. J quitossomose mansoni. Sio Paulo, Sander Edit. Purusitol59:111, 1973. Livros Medicos Ltda. e Universidade de SZo Paulo, (35) Cawston, F. G. Wild birds as a cause of the 1970. spread of bilharzia infection. J Trap Med 24:109, (22) Paraense, W. L. The distribution of the 1921. molluscan vectors of schistosomiasis in the