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PubMed1996

Polymerase chain reaction for detecting Onchocerca volvulus in pools of blackflies.

The detection of Onchocerca volvulus infected simuliids or blackflies is routinely done by dissection and microscopic examination of individual flies, but this method is tedious and time consuming. Here we describe a method of detecting single O. volvulus infected blackflies in pools of uninfected blackflies. Using a PCR with Onchocerca specific primers it is possible to reproducibly detect one heavily infected blackfly in a pool of 80 flies, or to detect one blackfly inoculated with one microfilaria in a pool of 20 flies. With the method described large numbers of blackflies can be rapidly screened for the presence of O. volvulus infected flies.

Animals↗
PubMed1997

Successful control of onchocerciasis with community-based ivermectin distribution in the Rio Santiago focus in Ecuador.

Onchocerciasis is a major blinding disease in equatorial Africa and Central and South America. Ivermectin is a safe and effective drug in the treatment of this disease and now forms the basis of disease control in most endemic areas. We report the findings of long-term control of this infection in the Río Santiago focus in Ecuador, between January 1990 and December 1996, using a strategy of giving ivermectin treatments biannually in hyperendemic communities and annually in meso- and hypoendemic communities. Ivermectin was administered by local health workers from each community. A high level of compliance to ivermectin was achieved, with 81.9% to 98.0% of those eligible receiving the drug at each treatment instance. The impact of ivermectin therapy was monitored using a cohort of 120 randomly selected infected individuals from 8 hyperendemic communities. The geometric mean microfilarial density of this group declined from 19.3 to 0 mf/mg over the 84-month observation period. Ivermectin had a significant impact on anterior segment ocular disease, acute onchodermatitis and sowda. The rate of infection of blackflies declined from 1.1% in 1989-0.08% in 1996, which is below the vectorial capacity of the Simulium vector and, as no new nodules were detected after 1994 and no children under 5 became infected over the observation period, it is likely that the transmission of this infection was interrupted in the study area.

Animals↗
PubMed1997

The effects of protease inhibitors and sugars on the survival and development of the parasite Onchocerca ochengi in its natural intermediate host Simulium damnosum s.l.

A range of protease inhibitors and carbohydrates were administered to the haemolymph of the vector Simulium damnosum s.l. to test for their effects on the success of an Onchocerca ochengi infection in vivo. We found that serine protease inhibitors led to a significant increase of parasite survival. Two sugars, D(+)-galactose and methyl-alpha-D-mannopyranoside, had the same effect. These effects are possibly due to the successful in vivo blocking of the two respective types of inducible immune molecules, the serine protease and the carbohydrate binding lectins, both of which have been identified in simuliids.

Animals↗
PubMed1998

Is apoptosis involved in mechanisms to eliminate Onchocerca ochengi during Simulium damnosum s.l. immune response?

Co-injection of the parasite Onchocerca ochengi and the caspase inhibitors z-VAD.fmk and boc-D.fmk into the natural vector Simulium damnosum s.l. led to significantly increased survival of the parasites. Subsequent in situ apoptosis detection assays demonstrated that in the case of boc-D.fmk the enhanced survival was due to a diminished apoptosis level of the microfilariae in vivo. Additional assays using O. ochengi microfilariae which were coinjected with serine protease inhibitors into S. damnosum s.l. revealed that certain serine protease inhibitors can reduce the level of apoptosis.

Amino Acid Chloromethyl Ketones↗
PubMed1999

The Simulium damnosum complex in western Uganda and its role as a vector of Onchocerca volvulus.

The status of onchocerciasis vectors in the former Ruwenzori focus in western Uganda was re-examined some 15 years after control measures against Simulium damnosum s.l. were suspended. The four cytoforms S. kilibanum, 'Sebwe', 'Nkusi' and S. pandanophilum were found. While the nonanthropophilic 'Sebwe' was still widely distributed in rivers north, east and south of the Ruwenzori, the only anthropophilic species and vector, S. kilibanum, had disappeared from most of its former habitats and was now restricted to two limited foci, where high biting densities were encountered. It was still a vector south of the Ruwenzori (Kasese focus), where 15.4% of the parous flies were infected with larval stages of Onchocerca volvulus and 34 infective larvae were found in the heads of 1000 parous flies. In the second focus along the Mahoma and Nsonge rivers, a chromosomally highly polymorphic population of S. kilibanum had replaced the former vector S. neavei, but does not act as a vector. Only 2.3% of the parous females were infected and just 1 infective larva was found in the heads of 1000 parous flies.

Animals↗
PubMed2001

Combined benefits of annual mass treatment with ivermectin and cattle zooprophylaxis on the severity of human onchocerciasis in northern Cameroon.

We studied the effect of 10 annual distributions of ivermectin for control of human onchocerciasis on the reduction of Onchocerca volvulus transmission by Simulium vector flies. Prevalence and infection load in the human population decreased, whilst the annual biting rates (ABR) of the vector remained unchanged. The annual transmission potential of infective larvae of O. volvulus fell to 40% of the pre-intervention level, but was still sufficient to maintain endemicity. However, recent immigration of herds of nomadic cattle into the study area has diverted the flies from man to cattle, creating an additional zooprophylactic effect. The predominant transmission of the bovine filaria O. ochengi to man also provides some concomitant cross-protective immunity against further infestations with O. volvulus. The effects of ivermectin on O. volvulus, combined with the zooprophylactic effects of the increased cattle population, have produced a complex beneficial influence on the transmission of human onchocerciasis.

Animals↗
PubMed1997

Onchocerciasis: clinical presentation and host parasite interactions in patients of southern Sudan.

BACKGROUND: Onchocerciasis, an infection by the filarial nematode Onchoverca volvulus, is widely distributed in tropical Africa and of great dermatologic interest. This study analyses the dermatologic presentation and tries to determine the correlations between clinical disease and host parasite interactions in onchocerciasis patients of the Southern Sudan. METHODS: We performed clinical and histopathologic investigations in patients with onchocerciasis in the Wau District, Bahr el Ghazal Province, Southern Sudan. As well as a detailed clinical skin examination, skin biopsies were taken, processed, and investigated for type and degree of host tissue response. Parasitologic, clinical, and histopathologic findings were evaluated. RESULTS: Onchocerciasis appears with a variety of severe skin lesions. Central is a pruritic rash. Long-standing cases develop extensive pigmentary changes and impressive signs of skin tissue exhaustion. Cellular host tissue responses to degenerating skin microfilariae seem to play a key role in the development of skin pathology. The degree of host response appears to be inversely proportional to the host's microfilarial load. CONCLUSIONS: Onchocerciasis represents a health problem of great dermatologic importance in Southern Sudan. The study results demonstrate clinical variations in onchocerciasis and provide support for the existence of a disease spectrum.

Adolescent↗
PubMed1987

[Ivermectin and the reduction of the rate of infection of simuliids in a forest focus of human onchocerciasis].

Eight patients from a forest onchocercian area "Grandes rivières", in Ivory Coast, were treated with a single oral dose of ivermectin (12 mg). The density of dermic microfilariae was estimated at days 0, 7 and 180; the mean numbers of ingested microfilariae and of developing larvae in the vectors S. soubrense-S. sanctipauli, engorged on the treated patients were recorded. Comparisons were made with non treated patients, having a similar density of microfilariae than the 8 treated patients at day 7. Results confirm the reduction induced by ivermectin of the dermic microfilarial density and the resulting reduction of the infection of the simuliids. Furthermore 7 days after treatment, a new phenomenon is demonstrated: for a similar dermic microfilarial density, simuliids take up a number of microfilariae 100 times lower from treated than from untreated patients. To explain this phenomenon, it is suggested that ivermectin induces a change in the microfilarial distribution in the layers of the dermis. Six months after treatment, this low uptake of microfilariae by the vectors had disappeared, and the infection rate of the engorged similiids was much higher than at day 7 although the dermic microfilarial density was similar.

Animals↗