Molecular evidence of "Siisa form", a new genotype related to Onchocerca ochengi in cattle from North Cameroon

Onchocerca ochengi, a filarial nematode parasite from African Zebu cattle is considered to be the closest relative of Onchocerca volvulus, the causative agent of river blindness. Both Onchocerca species share the vector, black flies of the Simulium damnosum complex. Correct identification of their infective third-stage larvae in man-biting vectors is crucial to distinguish the transmission of human or animal parasites. In order to identify different closely related Onchocerca species we surveyed the sequences from the three mitochondrial loci 12S rRNA, 16S rRNA and coxI in both adult worms isolated from Onchocerca-induced nodules in cattle and infective third stage larvae isolated from vector flies from North Cameroon. Two distinct groups of mitochondrial haplotypes were found in cattle as well as in flies. One of them has been formerly mentioned in the literature as Onchocerca sp. 'Siisa', a filaria isolated from the vector S. damnosum sensu lato in Uganda with hitherto unknown host. Both variants are found sympatric, also in the same nodule of the animal host and in the vector. In the flies we also found the mitochondrial haplotype that had been described for O. volvulus which is about equally different from the two previously mentioned ones as they are from each other. These results suggest a higher genetic diversification of Onchocerca ochengi than previously reported