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  • Title: Successful control of onchocerciasis vectors in San Vicente Pacaya, Guatemala, 1984-1989.
    Author: Ochoa JO, Castro JC, Barrios VM, Juarez EL, Tada I.
    Journal: Ann Trop Med Parasitol; 1997 Jul; 91(5):471-9. PubMed ID: 9329983.
    Abstract:
    Between 1984 and 1989, the onchocerciasis-vector control zone on the pilot area of San Vicente Pacaya, Guatemala, which had been subject to experimental control since 1979, was extended from 91.3 to 148.6 km2. Temephos was used as a larvicide against Simulium ochraceum s.l. the target species. As a new strategy, only breeding sites with water discharges of 0.1-10 litres/s were treated, every 2 weeks. This approach provided a substantial reduction in effort, number of treated sites, time and cost. To assess the effect of the temephos, nine sites were selected in which standardized collections of adult Simulium were made twice a month, by human bait. There was an obvious difference between the pre- and post-control mean densities of flies at each site. In the northern area, which includes the Lavaderos, Barretal, Colina and Rodeo sites, the biting density in 1979, before treatment, varied between 10 and 64 flies/man-hour (FMH). Four years later, this had been reduced to 0.1-3.2 FMH, and by the end of the present study, in 1989, the mean density was zero FMH. In the southern area, which lies south-east of Lavaderos (and includes Guachipilin, Ingerto, Pena Blanca and Sierra Morena), the density during the pre-control phase was 24 FMH at one of the two sites investigated at the time and 39.3 FMH at the other. It fell to 0.1-0.5 FMH after 5 years of control and to zero (three sites) or close to zero (< or = 0.5 FMH; one site) for the last 4 years of the present study. To assess the effect of vector control on onchocerciasis prevalence and incidence, 1280 residents from six endemic communities, out of 12,000 permanent inhabitants, were examined. In Santa Cruz, Patrocinio and Los Rios, the prevalence of skin microfilariae in the subjects from each community fell from 8.1%-37.8% during the pretreatment, base-line period to 0.0%-31.5% when the study foci were totally integrated into the vector-control operation following treatment. Incidence among children (aged < or = 9 years) varied from 0%-25% for the period 1982-1984 but, thereafter, not a single case appeared in four of the six study communities (Santa Cruz, Patrocinio, Los Rios and Berlin). Incidence in Guachipilin did not decline appreciably, probably because of human migration into the area from other onchocerciasis foci. The prevalence of nodules followed a similar trend to those of the prevalence and incidence of skin microfilariae, falling from 9.1%-45.0% pre-control to 1.8%-14.3% 10 years later. In the onchocerciasis vector control zone in San Vicente Pacaya, Guatemala, temephos was the only insecticide used against Simulium ochraceum during 1979-89. A shift to a strategy of treating only breeding sites with water discharges of 0.1-10 liters/s every 2 weeks resulted in considerable reductions in program effort, number of treated sites, time, and costs. To evaluate the effect of the temephos, 9 sites in which standardized collections of adult Simulium were made twice a month were selected. In the northern sites (Lavaderos, Barretal, Colina, and Rodeo), the biting density before the temephos treatment program was initiated in 1979 was 10-64 flies per man-hour. This density had been reduced to 0.1-3.2 by 1983 and to zero by 1989. In the southern area (Guachipilin, Ingerto, Pena Blanca, and Sierra Morena), pre-intervention biting densities were 24.0-39.3 flies per man-hour, but dropped to 0.1-0.5 by 1993 and to 0-0.5 by 1989. Moreover, examination of 1280 residents from 6 endemic communities revealed a decline in the prevalence of skin microfilariae from 8.1-37.8% in the baseline period to 0-31.5% when the study foci were integrated into the vector control operation after treatment. After 1984, 4 of these communities had no cases of onchocerciasis among children 9 years of age and younger. The prevalence of nodules fell from 9.1-45.0% in the pretreatment period to 1.8-14.3% in 1989. These findings confirm that larviciding with temephos has produced excellent control of onchocerciasis in San Vicente Pacaya.
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