Anthropophily, zoophily and roles in onchocerciasis transmission of the Djodji form of Simulium sanctipauli and S. squamosum in a forest zone of Togo.

Adult female Simulium damnosum s.l. were caught at human and cattle bait at Djodji in Togo. Two members of the Simulium damnosum complex, the Djodji form of S. sanctipauli (74.9% of the total catch) and S. squamosum (25.1%), were identified and both were mainly anthropophilic. Although each species was also recorded feeding on cattle or turkey baits, most flies which were caught at animal baits did not take blood from them. Flies caught unfed at the cattle bait tended to be larger and have higher parous rates than those caught on man. S. sanctipauli flies were on average larger than S. squamosum but the sizes of both species varied seasonally. Infections with Onchocerca volvulus were found in both species. The infection rates varied seasonally with the highest levels occurring in the wet season. The Djodji form of S. sanctipauli is potentially a much more efficient vector (162 L3/1000 biting flies) than both S. squamosum (48 L3/1000 biting flies) and the S. sanctipauli s.l. found in the Cote d'Ivoire.

A DNA sequence specific for forest form Onchocerca volvulus.

Onchocerciasis, or river blindness, is caused by infection with Onchocerca volvulus, a filarial parasite which infects about 40 million people in Africa and Latin America. Epidemiological, clinical, entomological and serological studies of African onchocerciasis led to the hypothesis that Onchocerca volvulus exists in different forms in the forest and savannah. It is uncertain if these differences are due to genetic differences within O. volvulus itself, or to epigenetic factors, such as differences in the host populations. To date no basic biochemical differences between the forest and savannah populations of O. volvulus has been found, although isoenzyme studies have shown that differences in allele frequency between forest and savannah populations exist. Here we describe the isolation of a DNA sequence that seems to be specific for the forest form of O. volvulus, the first indication of a basic genetic difference between the savannah and forest forms.

The prevalence of Onchocerca spp. in cattle in northern Togo in 1979.

The prevalences of three species of Onchocerca parasitising the Somba race of cattle occurring in the Kara region in northern Togo were investigated. Onchocerca ochengi was common in the cattle rearing areas of Keran (42% of head infected) and Kozah (29% of head infected). The prevalences of O. dukei ranged from 35 to 73.5% and of O. gutturosa from 23.2 to 49.1%. No differences were noted in the percent of bulls and cows parasitised.

[Two new nodular Onchocerca spp. in wild Bovidae, in Upper Volta (author's transl)]. / Deux nouvelles onchocerques nodulaires chez des Bovidés sauvages, en Haute-Volta.

Description of two new Onchocerca from wild Bovidae, O. schulzkeyi n. sp. and O. hamoni n. sp., respectively parasite of Hippotragus equinus and Kobus (A.) kob; both species have been recorded in the Volta region, where human onchocerciasis is prevalent. O. schulzkeyi and O. hamoni are located in respectively, dermic and subcutaneous nodules, the females of both species are devoid of cuticular rings. Those two new species belong to the line of O. volvulus and nodular Onchocerca of Bovinae. This finding suggests that, as for O. ochengi, they can disturb the evaluation of the annual potential of transmission, necessary in the epidemiological studies concerning the human onchocerciasis.

The development of Onchocerca ochengi (nematoda: filariodea) to the infective stage in Simulium damnosum s.l. with a note on the histochemical staining of the parasite.

Onchocerca ochengi, an intradermal filarial parasite of cattle in Africa, was shown to develop normally to the infective stage in a member of the Simulium damnosum complex, almost certainly S. sanctipauli. The development of the parasite in the thoracic musculature and head of the fly was completed in 6 days at an ambient temperature of 25-30 degrees C. The larvae were very similar in rates of development, morphology and distribution to those of the human parasite O. volvulus in the same vector. No histochemical differences were found in the enzyme staining of O. ochengi distinct from the pattern described earlier for O. volvulus.

[Observations on the life cycle of O. ochengi in Simulium damnosum s.l. in Togo (author's transl)]. / Donnees sur le cycle d'Onchocerca ochengi chez Simulium damnosum s.l. au Togo.

In the focus of human onchocerciasis in Togo (Mono River), the authors collected 250 Simulium damnosum s.l. engorged on a cow parasitized by O. dukei, O. ochengi, O. gutturosa and O. armillata. On 39 Simulium damnosum dissected 24 h after the blood meal, 5 had ingested O. gutturosa, 1 O. armillata, 18 O. dukei and 6 O. ochengi; only for O. ochengi, the microfilariae have reached the hemocoel (3. S. damnosum on 6). From 48 h to 5 days, 6 on 132 S. damnosum contained developing larvae (2 Simulium with young first stage larvae at 48th hour; 1 with young first stage at 3rd day; 1 with first molting at 4th day; 2 with second molting larvae at 5th day). From 6th to 9th days, 2 Simulium on 89 have infective stages. All these larvae cannot be distinguished from those of O. volvulus. A good presumption does exist that O. ochengi can develop in S. damnosum: crossing of the stomach wall only by these microfilariae, presence of larvae of which the development-stage corresponds to the moment of the blood-meal, observation of the second molting five days later. It is difficult to ascertain that the three infective stages observed from 6th to 9th day pertain to O. ochengi, because the presence of a natural (human or animal) infestation; but it appears quite impossible that larvae which can develop to the second molting cannot be transformed in an infective stage.