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PubMed1985

A field method for the procurement of infective larvae of Onchocerca volvulus.

Natural vectors of onchocerciasis (S. yahense) were collected. Ninety-eight were intrathoracically inoculated with 30 freshly obtained skin-dwelling microfilariae. Of the 82 flies dissected, 56 were infected and 28 harbored infective larvae. A total of 193 infective O. volvulus larvae were obtained. The mean infective worm burden was 6.9.

Humans↗
PubMed1992

Ivermectin: reduction in prevalence and infection intensity of Onchocerca volvulus following biannual treatments in five Guatemalan communities.

Residents of five hyperendemic communities located in the central focus of onchocerciasis in Guatemala were treated with ivermectin (Mectizan) or placebo every six months for 30 months. The effects of treatment on prevalence and the intensity of skin infection (microfilarial skin density [MFD]) were evaluated. Significant and persistent reductions in both of these indices were achieved by coverage of 80.7% of the eligible populations. The highest proportionate reductions in both indicators of infection occurred after the first treatment, followed by more gradual decreases through the fourth treatment. In one community in which the mean coverage was 92.7%, prevalence decreased from 74.0% at pretreatment to 34.9% after four treatments, while the MFD decreased from 7.8 to 2.0; reductions of 52.8% and 74.3% from pretreatment values, respectively. In every ivermectin-treated community except one, in which drug acceptance was low, the mean community MFD values were reduced to the level associated with low infectiousness for the vector, Simulium ochraceum. Moreover, the category of MFD associated with high vector infectiousness was reduced at least ten-fold over the pretreatment level. One community had low participation during the first two treatments (32.8% and 22.7% of those eligible). This increased to 55.2% at the third treatment because of implementation of an educational program describing both the disease and the beneficial effects of ivermectin and because skin biopsies and nodulectomies were not performed. Secondary reaction rates for all communities were 29.5%, 9.9%, 10.3%, 8.2%, and 7.1% for the first through fifth treatments, respectively. Pruritus was the most common (34.0%) secondary reaction, followed by facial edema (31.8%). All reactions were classified as mild to moderate. Recommendations for mass distribution of ivermectin in Guatemala are given.

Adolescent↗
PubMed1995

Vector competence of Simulium exiguum for Onchocerca volvulus: implications for the epidemiology of onchocerciasis.

In the transmission of human onchocerciasis, competence of the black fly vector influences intensity of transmission by regulating how many infective-stage larvae are produced. The disease is intensifying in Ecuador where Simulium exiguum is a highly efficient limitation-type vector comparable with African forest species in terms of the percentage of flies developing infective-stage larvae and the numbers of larvae per infected fly. In contrast, the endemic foci in Guatemala and southern Mexico have remained stable and closely circumscribed around larval development sites for S. ochraceum, a vector that exhibits a facilitation type of competence and must feed on people with comparatively high microfiladeremia to develop significant numbers of infective-stage larvae. This comparison indicates that assessments of vector competence should be included when planning regional control programs for onchocerciasis.

Adult↗
PubMed1998

Prevalence of Onchocerca volvulus nodules in the Sankuru River Valley, Democratic Republic of the Congo, and reliability of verbal assessment as a method for determining prevalence.

The epidemiology of onchocerciasis in much of the Democratic Republic of the Congo (formerly Zaire) is not well established. We report the results of an onchocerciasis rapid assessment survey carried out in 18 villages of the Sankuru River Valley in the central part of this country in preparation for mass distribution of ivermectin. Thirty men from each village were randomly selected and examined for subcutaneous nodules. The prevalence of nodules among these men in each village ranged from 82.5% to 100% with a mean prevalence of 95.0%. This study also assessed the validity of using verbal assessment instead of physical examination to determine prevalence of nodules. This verbal method had a sensitivity of 93.5% and a specificity of 83.3%. High sensitivity and specificity for this method suggest that it might be a cost-effective approach to determine the prevalence of onchocerciasis over large areas without using physical examinations requiring medical personal. This approach could be particularly useful where the coverage of health services is poor. The use of the Global Positioning System made it possible to send coordinates and survey data electronically to World Health Organization personnel in Geneva for computer generation of prevalence maps. The use of river boats to conduct surveys and support ivermectin distribution in the Congo is discussed.

Adult↗
PubMed2004

Preliminary studies on the biting activity and transmission of Onchocerca volvulus by Simulium neavei (diptera: simuliidae) in Kashoya-Kitomi focus, Western Uganda.

OBJECTIVE: To determine the biting activity and onchocerciasis transmission in Kashoya-Kitomi focus, Western Uganda. DESIGN: Cross-sectional survey in randomly selected sites. SETTING: Three districts in Western Uganda. METHOD: Crab trapping and examination for immature stages of Simulium neavei and full day human bait catches and dissections were conducted at three sites. RESULTS: A total of 338 crabs were caught and out of this 372 (95.9%) were positive with immature stages of S. neavei with mean S. neavei/crab of 6.9. High biting density of S. neavei was observed in the two sites in Kabarole and Mbarara districts whereas an extremely low density was observed at a site in Bushenyi. Diurnal biting pattern revealed two peaks in the morning (09:00-10:00 hours.) and in the late afternoon (14:00-15:00 hours.) with a mid-day lull. The infection/infective rates were 53.3/11.0%, 30.7% to 7.8% and 20.0/0% for sites in Mbarara, Kabarole and Bushenyi districts, respectively. Monthly biting rates/ Transmission potentials for Mbarara, Kabarole and Bushenyi districts were 6231/5437, 9244/2916 and 247/0. CONCLUSION: There was high transmission of onchocerciasis observed in Kashoya-Kitomi focus despite the ongoing ivermectin treatment. The need for improved chemotherapeutic coverage and instituting other control measures may be necessary.

Animals↗
PubMed1975

[Investigations on the filariidae of the cervidae in Southern Germany. 1. Development of the nodule, finding of the sexes and production of the microfilariae in Onchocerca flexuosa (Wedl, 1856), in the red deer (Cervus elaphus) (author's transl)].

The biology of O. flexuosa was studied during the examination of numerous subcutaneous nodules, which were taken from the hides of red deer of all age-classes. In fawns the development of the nodule is induced by the immature stages, probably by the females. At the same time a hematome is formed. Males of different ages penetrate into the nodule where mature or immature females are present. Later they mate and remain within the nodule until the microfilariae in the uteri of the females develop. Usually 1 or 2, occasionally 4 females are found together. During the development of the embryos in the uteri the initially stretched female winds up. Only a short anterior part remains always straight. It is put out through the wall of the capsule in order to release the microfilariae. The males are often the majority reaching to 13 in one nodule. During the release of the microfilariae the males are found outside the nodule on the surface or near-by in the subcutaneous connective tissue. Both sexes are able to mate a second time. In older deer the males are also able to induce the development of nodules.

Aging↗
PubMed2002

Co-infection of Onchocerca volvulus and intestinal helminths in indigenous and migrant farmers in southwest Ethiopia.

A cross-sectional survey on onchocerciasis and intestinal helminthic infections was conducted in two villages around the town of Teppi, south-west of Ethiopia on a total of 308 subjects of which 180 indigenous and 128 migrant settlers aged 10 years and above who lived in the area for at least 5 years. Of the total study subjects, 65% were males. The majority (64%) of the study subjects were in the age range of 21-40 years. The results of stool and skin snip examinations for ova/parasite and microfilaria revealed that, 62% (190) and 81% (248) of the study subjects were positive for intestinal parasites and microfilariderma respectively. Fifty percent (154) of the total subjects in the two villages had both onchocerciasis and intestinal helminthic infections. However, 80% (94/118) of the stool negative subjects also had onchocerciasis indicating that onchocercal skin infection has no significant influence on the acquisition of intestinal helminthic infections or vice versa [(relative risk 1.04, 95% CI 0.91, 1.18) P > 0.05]. Sixty-five percent (161/248) of the total skin snip positive individuals had microfilarial load of > 10 mf/mg of skin snip. The proportion of multiple infections with 2 or more intestinal helminthes was recorded in 51% (96/190) of individuals positive for intestinal parasitosis. There was a significant (x2 = 8.41, P < 0.005) difference in the onchocerciasis infection rate among indigenous (88%) and migrant (75%). No direct association was observed between onchocerciasis and intestinal parasitosis in the two study groups (indigenous and migrant settlers). The public health significance of coexistence of the two diseases, and the need for intensive control measures are discussed.

Adolescent↗
PubMed2002

Detection of Onchocerca volvulus infection in low prevalence areas: a comparison of three diagnostic methods.

The standard assay for onchocerciasis diagnosis is microscopical detection of microfilariae in skin snips. Skin snipping is painful, requires appropriate sterilization of equipment, and may fail to diagnose light infections. Two alternatives are a polymerase chain reaction (PCR) test which detects parasite DNA in pieces or scrapings of skin and a test based on allergic reactions to topical application of diethylcarbamazine (DEC). We compared these 2 diagnostics with standard skin snip microscopy in 313 individuals from 2 villages in Guinea, with low prevalence after over 10 years of control by the Onchocerciasis Control Programme. Lower and upper bounds on sensitivities and specificities of these 3 tests were estimated. In addition, these parameters were estimated using 5 different statistical models. Where prevalence was low, PCR and the DEC patch test appeared to be more sensitive than skin snipping which has low sensitivity. As the DEC test is non-invasive, simple and cheap, it may provide a good alternative to skin snipping alone for surveillance in low prevalence areas.

Adolescent↗