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Ngaoundere Gudali zebu cattle naturally exposed to Simulium damnosum s.l. and Culicoides spp. bites were examined during 4 years for O. ochengi adult worm acquisition, Onchocerca ochengi and Onchocerca gutturosa skin microfilaria dynamics, and IgG1 and IgG2 antibody subclass responses. Eleven animals acquired a total of 465 O. ochengi nodules (average of 17 per female and 72 per male). The O. ochengi nodule load was highly variable in individual animals and exacerbated in mature male cattle. Three patterns of acquisition of O. ochengi (resistant to new infestation, early susceptibility and late susceptibility), not associated with Simulium biting intensity (P > 0.05), were distinguished. The minimum prepatent periods for O. ochengi nodules, O. ochengi microfilariae and O. gutturosa microfilariae were 10, 20 and 21 months, respectively. The O. ochengi microfilaria density significantly (P < 0.001) increased with age, was higher in young mature bulls than female animals (P < 0.001) and finally reached highest levels (P < 0.005) during the dry season. Antibody responses to Ov10/Ov11 recombinant O. volvulus antigens were predominantly of the IgG1 subclass. High levels of this subclass (not IgG2) observed in new born calves declined to almost zero levels at the age of 5-8 months but IgG1 levels significantly increased (P < 0.05) with age subsequently during patency. Put together the acquisition and accumulation of O. ochengi parasites in zebu cattle, apart from being season, sex (gender) and host age associated, may also suggest a density-dependent regulation of parasite establishment in a proportion of the exposed population.

We studied the biting densities of Chrysops silacea and the transmission of loiasis over 1 year in a regenerated forest in the south-west province of Cameroon. A total of 3015 flies caught near a wood fire at ground level during rainy and dry seasons were identified morphologically and 1975 caught during the rainy season were dissected to determine their physiological age and infection rate. The prevalence of microfilaraemia in the human population in the study area was determined using the thick blood smear method. Chrysops silacea was the only species caught. The daily and seasonal biting cycle of C. silacea showed two peaks of activities, 9-11 a.m. and 2-4 p.m. The biting cycles of parous and nulliparous flies showed the same trends, but the density of nulliparous flies biting at all time of the day was 2-3 times higher. Chrysops silacea biting density was high during the rainy season (9.06 +/- 6.88 flies/man/h) and lowest during the dry season (0.44 +/- 0.75 flies/man/h). An infection rate of 1.72% and a monthly morning and afternoon transmission potentials of 120769.11 and 139016.64 infective head L3/man were observed, respectively, in the rainy season. Even though few Chrysops carried Loa loa infective larvae (0.7%), their parasite load was high, giving a high level of transmission of L. loa in the area. A total of 20.37% of the people examined for blood microfilariae were positive. These results suggest that the study area is an active focus of loiasis transmission.

A longitudinal study on malaria vectors and transmission was carried out in a forest-savannah transitional area in Cameroon. Indoor all night mosquito collections on human bait were performed during one year in two villages: Nditam and Ngoume. Nditam was located in a secondary forest block surrounded by savannah, while Ngoume was situated in an ancient forest block. The results showed that at Nditam, only one anopheline species was collected, that was Anopheles gambiae s.l.. The average daily biting rate was 2.4 bites per man per night. The sporozoitic index of An. gambiae was 9.4%. The entomological inoculation rate was therefore estimated at 0.225 infective bite per man per night that is to say 82 infective bites per man per year. Malaria transmission was low during the year, but an important increase was observed in September, when the rainfall was at its peak. At Ngoume, no Anopheles mosquito was collected. Therefore, malaria transmission was not observed in that village.