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An Entomologic and Parasitologic Survey for Onchocerciasis in Western El Salvador
D. P. Wilton
D. P. Wilton
Central America Research Station, Bureau of Tropical Diseases, Center for Disease Control, Public Health Service, U.S. Department of Health, Education, and Welfare, San Salvador, El Salvador, C.A.
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R. C. Collins
R. C. Collins
Central America Research Station, Bureau of Tropical Diseases, Center for Disease Control, Public Health Service, U.S. Department of Health, Education, and Welfare, San Salvador, El Salvador, C.A.
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Despite similarities of topography and climate in the coffee-producing regions of the two countries, human infection with Onchocerca volvulus has rarely been reported in El Salvador, whereas onchocerciasis has long been endemic in the coffee plantations of neighboring Guatemala. The apparent near absence of the infection in El Salvador was investigated in a coffee-growing area in the western part of the country some 50 km from Guatemala's principal onchocerciasis zone. Collections of black flies attracted to humans and, for comparison, to horses were made for 1 yr at elevations from 300–1,330 m, and a skin biopsy survey was conducted among area residents ranging in age from 10 yr to over 60 to estimate the prevalence of microfilarial skin infection. Simulium metallicum and S. callidum accounted for 77 and 21%, respectively, of the flies collected from humans and 87 and 11%, respectively, of those from horses. Both species showed a marked preference for horses as a source of blood. When coming to feed on humans, they chose the legs more often than the shoulders as a feeding site. Other species, which together made up only 2% of the 5,507 flies collected, were S. downsi, S. pulverulentum, S. mexicanum, and S. haematopotum. The highest landing rates recorded for both S. metallicum and S. callidum on humans were at collecting sites from 600–940 m elevation during the October-February period which spans the annual transition from wet to dry seasons. The absence of S. ochraceum from the collections is noteworthy. This anthropophilic black fly frequently attains very high densities in Guatemala, where it is regarded as the principal vector of O. volvulus. No microfilariae were detected in skin biopsies from 941 study area residents, indicating that no significant reservoir of infection exists there and, together with the entomologic data, supporting the assumption that the region is free of endemic human onchocerciasis.
Author Notes
Present address: Vector Biology and Control Division, Bureau of Tropical Diseases, Center for Disease Control, Atlanta, Georgia 30333.
| Past two years | Past Year | Past 30 Days | |
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