Transmission of Human and Animal Onchocerciasis and Molecular Diagnosis of Onchocerca Species in some Ghanaian Communities

Abstract

Control of onchocerciasis over the past 3 decades has brought great relief to millions of people living in endemic communities, by substantially reducing blindness and other dermatological lesions. However, there are still areas where infections in human populations are high and vector transmission is ongoing, requiring a further understanding into the transmission dynamics of the disease in such communities. Furthermore the status of animal onchocerciasis is still unknown in Ghana even though there is a high cattle population in our human onchocerciasis endemic areas who serve as reservoirs for animal onchocerciasis (Onchocerca ochengi) as well. Adult female black flies were caught for microscopic assessment of infection in 12 onchocerciasis endemic communities in the dry season months of March, 2014 and February, 2015. Animal onchocerciasis was assessed in nineteen cows from three endemic communities for the presence of O. ochengi. Molecular biology techniques were employed to assess the status of infection in cattle while onchocercal larvae was introduced to nulliparous black flies and processed for molecular identification of onchocerca spp. A total of 9,343 adult female black flies were collected from all the 12 communities. The Monthly biting rates in all 12 communities were above the WHO threshold biting rate (TBR) of 1000 bites per person per annum in 2014, while in 2015, seven communities had MBR above the WHO threshold. Out of a total of 2,046 parous flies dissected, only 5 infective flies (0.05 %) were found, these flies harboured 11 third stage infective larvae which were all from Agborlekema I. Also, Onchocerca microfilarial infections in cattle were found only in Agborlekema I. The PCR-based assay carried out based on 12S mitochondrial RNA gene using DNA from microfilaria obtained from cattle have validated the presence of Onchocerca ochengi while DNA obtained from larvae obtained from black flies have validated the presence of onchocercal species in the vector in Ghana. Since black fly vectors transmit various Onchocerca spp., including O.ochengi and O. volvulus, it is possible that the infected cattle at Agborlekema I might have contributed to most of the transmission recorded in this study. It is therefore necessary that transmission studies should consider molecular diagnoses of infective Onchocerca larvae. This will help evaluate the goal of elimination efforts in Ghana. Further studies are required to discriminate O. volvulus from O. ochengi.