Blood-meal identification and impact of blood feeding on femalespecific esterase in the Anopheles funestus group

Abstract

South Africa is experiencing low-level residual malaria transmission in Limpopo, Mpumalanga, and KwaZulu-Natal. This is partly due to outdoor biting and resting of Anopheles species that are not affected by the indoor spraying of insecticides. Anopheles funestus of the An. funestus group is a major malaria vector in southern Africa, while other species of the group, aside from An. rivulorum-like, have been implicated as secondary vectors. It is necessary to investigate the potential role of An. funestus group species in malaria transmission in South Africa in order to reduce incidences of malaria. This requires understanding the blood (host) feeding preferences of Anopheles species as well as understanding the underlying factors, such as esterase activity, linked with blood feeding biology. Wild caught An. funestus group specimens collected from Mamfene area in KwaZulu-Natal were identified to species level using An. funestus speciesspecific polymerase chain reaction (PCR). The presence of Plasmodium falciparum in the female specimens was examined using a P. falciparum circumsporozoite ELISA. The specific host preference(s) (human, cattle, goat, pig, dog and chicken) of the wild female specimens was studied using blood meal PCR. The impact of climatic factors (temperature, relative humidity and precipitation) on the specimens’ host preferences was also analysed. Finally, the link between blood feeding of laboratory colonised An. funestus s.s. and its esterases’ activity was determined using an isoenzyme electrophoresis assay.

A total of 826 females representing four An. funestus group species (An. leesoni, An. parensis, An. rivulorum and An. vaneedeni) were identified, with An. parensis being the most common species. None of the females were infected with the malaria parasite nor had they fed on humans. These members of the An. funestus group showed a clear preference for cattle and climatic parameters did not influence the host feeding preferences. Increase in esterases activity (EST-9, -7, -4, and -1) was observed after blood feeding of laboratory colonised An. funestus s.s. females. In conclusion, members of the An. funestus group collected from Mamfene, which have previously been implicated as secondary malaria vectors, did not feed on humans and were not infected with P. falciparum. This lowers the role of these species in malaria transmission for KwaZulu-Natal. However, entomological surveillance of Anopheles species should continue to increase sample size and provide the malaria vector control with scientific evidence to guide future activities. This study also demonstrated that blood feeding influenced specific esterases activity in a major malaria vector An. funestus. Further analysis of these esterases’ activity and their link with blood feeding is necessary as it could provide essential information regarding the An. funestus vectorial capability.