Status of schistosomiasis in the Caribbean

A

BSTRACTS AND REPORTS

S

TATUS OF SCHISTOSOMIASIS

IN THE CARIBBEAN

Manson’s schistosomiasis has probably existed in the Caribbean subregion for more than three centuries. The infec- tion is believed to have been introduced to the Western Hemisphere with enslaved West Africans in the seventeenth through nineteenth centuries, but the presence of the parasite, Schistosoma mamoni, remained unrecognized until endemic infection was discovered in three countries of continental South America and several Caribbean islands at the beginning of the present century (Figure 1).

Organized research and control activi- ties for schistosomiasis in Caribbean countries were begun in the 1950s and achieved some notable successes. The infection was eradicated from Vieques (an island municipality of Puerto Rico) and from St. Kitts and St. Maarten, although on these latter two islands this result was incidental to habitat changes rather than a consequence of deliberate attempts at eradication. Ma- jor control programs led to marked reductions in disease incidence in Puerto Rico and Saint Lucia; in the former country the efforts were greatly assisted by concomitant improvement in socioeconomic conditions.

As understanding of the local epide- miology of S. mamoni improved, it became increasingly apparent that the distribution of the infection was dynamic. The parasite had extended its range within certain counuies and had recently become established on some islands where it had not previously been reported. The intermediate host snail had similarly colonized new island foci. Thus, Manson’s schistosomiasis came to be recognized not merely as a health problem for those countries where endemic foci of infection already exist, but also as a potential problem in those neighboring countries where conditions are appropriate to support transmission.

FIGURE 1. Endemic areas and areas at risk for the introduction of schistosomiasis in the Caribbean subregion.

Endemic areas l!iBza Areas at risk

G -.

‘+ D

%

- ANTIGUA b MONTSERRAT

. GUADELOUPE

e ₀

1

MARTINIQUE %

SAINT LUCIA 4

b ST. VINCENT ,

ANDTHE l

GRENADINES .’ 0

GRENADA @ I ba eTRINIDAD

9 _AND ---) TOBAGO

definition of the subregion. The objective of this report is to strengthen and encourage the perception of schistosomiasis as a subregional health problem.

Endemic Areas

Antigua and Barbuda. Transmission has been verified in only a small, central area of Antigua, although the intermediate host, Biomphalank gZa- &rata, is found in pools and reservoirs throughout the island. The extensive impoundment of water has reduced the risk of transmission because human

contact with the potential foci is limited. Increased transmission may result if the new reservoirs become important recreational areas.

Dominican Republic. Schistosomiasis is currently endemic in this coun- try. Transmission foci and intermediate host snail habitats are widely distrib- uted, and 4.5 % of the population is potentially exposed to the infection. The recent discovery of additional foci may represent expanding distribution or a stable situation that has been inadequately surveyed. No data are avail- able on the public health significance of the disease. No integrated control activities are under way, and neither morbidity nor public health impact has been assessed. Treatment is available for individual cases.

Guadeloupe. Thirty-six percent of the population of Guadeloupe lives in three major endemic areas where active schistosomiasis transmission occurs. The proportion of the population at immediate risk of infection is probably lower, however, as the active foci are rarely visited, are isolated from the ma- jority of rural dwellings, and have a restricted distribution. Control activities, including identification of foci, improvement in sanitation services, and health education programs, have been initiated with the aim of reducing both morbidity and prevalence. Reservoir hosts (Ruttzcs spp.) are believed to maintain transmission in at least one endemic area, which may hamper con- trol efforts.

Martinique. Approximately 17.5 % of the population lives in areas of po-

tential transmission. Biompbahnh stramineu, which is resistant to infection, appears to have replaced B. gZabrata in most natural habitats, and the latter mollusk remains only in artificial environments where the likelihood of transmission of the parasite to man is low. Current and planned control ef- forts should substantially reduce the prevalence of infection.

Montserrat. The national distribution, prevalence, and public health sig- nificance are not well known, although it appears unlikely that schistoso- miasis presents a significant health threat. Only 1.3 % of the population lives near the supposed site of active transmission. No formal control programs are proposed. All persons identified as infected during surveys carried out in

1979 and 1981 were treated with oxamniquine.

ever, conditions remain suitable for transmission, and recrudescence is a con- tinuing possibility. An estimated 12.2 % of the population lives in areas of potential transmission. Maintenance control and surveillance programs have been in operation since 1981.

Suriname. Despite control activities, schistosomiasis remains endemic in coastal areas (the most densely populated areas

of

in sites of active transmission. Control activities centering on identification and treatment have resulted in reductions in both morbidity and prevalence. The provision of protected water supplies to endemic areas is expected to achieve further gains, although water management during the rainy season remains problematic. Planned maintenance activities include research into biological control methods and an investigation into the role of reservoir hosts.

Areas at

Risk

t Dominica. A susceptible intermediate host (B. gzabrata) is already estab- lished in natural water systems. Its rate of spread has apparently been slowed by severe and frequent flooding of the habitat and, possibly, by competition with other mollusks. Sanitation conditions and household contact with natu- ral waters are compatible with the transmission of infection, and human travel to neighboring endemic countries is frequent. ,

French Guiana. Susceptible B. glabrata are already present in French Guiana, but are confined to a few artificially modified habitats. Two major freshwater development projects may make new habitats available. The in- fection could then potentially be introduced from Suriname.

Grenada. The island offers ideal environments for Biomphudark gl’abrata, but the presence of the competitor snails B. straminea and Tbiara granzjcra may prevent its establishment. The low susceptibility of indigenous B. straminea makes this species an improbable alternative intermediate host. However, if the infection is introduced, transmission would be likely given the frequency of domestic contact with the snails’ habitat.

Haiti. Susceptible B. glabruta occur in an area of Haiti where sanitation and water contact conditions are suitable for transmission of Schistosoma munsoni. Large numbers of Haitian agricultural workers are potentially ex- posed to infection while working in the Dominican Republic each year and could introduce the infection to Haiti. The risk of establishment of schistoso- miasis in Haiti is very high.

ity of the introduction of infection is low, but if it were introduced, current levels of domestic water contact would ensure transmission.

Trinidad and Tobago. The potential intermediate host present (B. straminea) is resistant to infection. Suitable habitats for B. glabrata are lim- ited. There is a low risk of introduction of infection, and levels of domestic water contact would be unlikely to support transmission.

Souse: Donald A. P Bundy, Caribbean Schistosomiasis Group; The Current Status of Schistosomiasis in the Caribbean Region: Endemic Areas and Areas at Risk: Pan American Health Organization, Washing- ton, D.C.. 1987.

R

EVISION OF

CDC/WHO CASE DEFINITION FOR ACQUIRED

IMMUNODEFICIENCY

SYNDROME-(AIDS)

:

The Definition of AIDS

The clinical and laboratory definition of AIDS has changed as documentation of the wide spectrum of clinical manifestations due to human immunodeficiency virus (HIV) has accumu- lated and as specific laboratory tests to detect HIV infection and immune deficiency have been developed.

The initial defmition of AIDS was de- veloped by the Centers for Disease Control (CDC) of the U.S. Public Health Service in 1982. It was subsequently accepted by WHO in 1985.’ However, use of this definition requires extensive laboratory (culture and/or histology) capability. Since developing countries often lack adequate laboratory facili- ties, there was a need for a definition of AIDS that would enable clinicians to diagnose this condition with maximum precision. As a result of a workshop held in Bangui, Central African Republic, in 1985, a WHO clinical defini- tion of AIDS in Africa was developed. AIDS cases reported to WHO are accepted if they meet either the CDC/ WHO definition or the WHO clinical definition.

In late 1987, the CDC definition was