Assessment of the infectivity of malaria parasites from asymptomatic school children to Anopheles gambiae mosquitoes in a high transmission area in Ghana

Asymptomatic carriage of malaria parasite is a major public health issue in Ghana and sub-Saharan Africa. These infections are mostly sub-microscopic and not detected by routine malaria screening methods. Asymptomatic malaria infection carriers serve as an infectious reservoir for malaria transmission. This study assessed the infectivity of asymptomatic children to Anopheles gambiae mosquitoes in a high transmission area in Ghana. Ninety-eight (98) healthy children were screened for malaria parasites by microscopy and PCR. Sub-microscopic gametocytes carriage was also determined using RT-PCR. Blood samples from asymptomatic parasite carriers were used in membrane feeding assays of laboratory colonies of An. gambiae mosquitoes. Infectivity was assessed by dissection of mosquito midguts and the mosquito infection rate and oocyst densities were recorded. The total participants that were asymptomatic for malaria was 73/98 (74.49%). Malaria parasite prevalence was 13.7% by microscopy and 78.08% by PCR. Sub-microscopic infections accounted for 64.38% (47/73) of the asymptomatic parasite carriers. No gametocytes were detected, however, the Pfg377 gene was observed in 33.33% (19/57) of the asymptomatic parasite carriers. Blood from 4 out of 19 asymptomatic carriers, associated with carriage of sub-microscopic gametocytes, were found to be infectious to the An. gambiae mosquitoes. The average oocyst density observed was 0.01, with an overall mosquito infection rate of 0.07. This data will be helpful in improving current malaria control efforts in Ghana.