Onchocerca ochengi is a nodule-forming filarial nematode parasite of cattle. It is the closest known relative of the human parasite Onchocerca volvulus, with which it shares the black fly vector Simulium damnosum. Onchocerca sp. BSiisa^ was described in black flies and in cattle and, based on limited mitochondrial sequence information, appeared to be about equally phylogenetically distant from O. ochengi and O. volvulus. Based on molecular genetic markers and apparent interbreeding, we later proposed that O. sp. BSiisa^ belongs to the species O. ochengi. However, we did not demonstrate directly that the hybrids were fertile, and we were still unable to resolve the phylogenetic relationship of O. ochengi, O. sp. BSiisa,^ and O. volvulus, leaving some concerns with the conclusion mentioned above. Here, we present fully assembled, manually curated mitochondrial genomes of O. ochengi and O. sp. BSiisa,^ and we compare multiple individuals of these two taxa with respect to their whole mitochondrial and nuclear genomes. Based on the mitochondrial genomes, O. ochengi and O. sp. BSiisa^ are phylogenetically much closer to each other than to O. volvulus. The differences between them are well within the range of what is expected for within-species variation. The nuclear genome comparison provided no indication of genetic separation of O. ochengi and O. sp. BSiisa.^ From this, in combination with the earlier literature, we conclude that O. ochengi and O. sp. BSiisa^ should be considered one species.

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SUMMARYThe proliferation and cytokine profiles of peripheral blood mononuclear cells (PBMC) from microfilaraemic (Mf þ ) subjects infected by Loa loa in response to antigens of several parasitic stages were compared with those from amicrofilaraemic (Mf ¹ ) individuals. While a strong lymphoproliferative response and consistent levels of both Th1 (IL-2, interferon-gamma (IFN-g)) and Th2 (IL-4, IL-5) type cytokines were observed in response to adult worm (AW) and microfilariae (Mf) antigen in Mf ¹ individuals, Mf þ subjects were characterized by a T cell unresponsiveness, including proliferation, cytokine production and IL-2 mRNA expression. Conversely, T cell responsiveness to mitogens and non-specific antigen were similar in the two endemic populations. Depletion of lymphocyte subpopulations indicated that T CD4 þ were mainly involved in the specific cellular response. In contrast to other cytokines, IL-10 was produced in response to all parasitic stages, in both Mf þ and Mf ¹ patients. Neutralization of IL-10 did not restore cytokine production in Mf þ patients, while B7 mRNA expression was similar between Mf þ and Mf ¹ subjects in response to Mf antigen, suggesting that IL-10 was not the only factor responsible for T cell unresponsiveness. Mf þ patients have lower Mf antigen-specific IgG levels compared with Mf ¹ , and there is a significant correlation between Mf antigen-specific antibodies and IL-5 responses. These findings suggest that Mf ¹ status is correlated with T helper responsiveness, including proliferation and production of both Th1-and Th2-type cytokines, whereas Mf þ status is characterized by unresponsiveness of the same cell population, induced and/or maintained by microfilariae.

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Onchocerca ochengi is a common parasite of cattle in savanna areas of West Africa and its adult stages inhabit intradermal nodules. We have exploited the accessibility of the macrofilariae to examine quantitative and qualitative differences in both the macro- and microfilariae (mff) in relation to age in naturally infected cattle. Autochthonous cattle at a site on the Adamawa plateau, North Cameroon, situated near a perennial Simulium damnosum s.l. breeding site, were examined in three age groups (1.5-2.5, n = 34; 3-5, n = 39 and greater than or equal to 8 years old, n = 21). Skin mff densities were assessed from ventral skin biopsies, total body counts of nodules were done by palpation and 1-4 nodules were excised from positive animals, collagenase digested and the numbers and condition of macrofilariae determined. Embryogenesis profiles (embryograms) were done on a representative number of female worms in each age group. The overall prevalence of infection in the study population was 71% for mff and 85% for nodules. Nodule prevalence increased significantly from the 1.5-2.5 to 3-5 years old groups, but no other inter-age prevalences were significantly different. While the mean number of nodules per animal increased with age, geometric means (gm) 3.7, 15.5 and 23.1, the skin mff density maximized in the middle age group and decreased significantly in the old animals (gm 15.8, 44.7 and 11.4 mff/g, difference between latter two parameters significant, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)