Malaria transmission potential of Anopheles mosquitoes in the Mwea-Tebere irrigation scheme, Kenya

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Abstract
2. Anopheles arabiensis Patton and A. funestus Giles were identified as vector of Plasmodium falciparum malaria in the Mwea-Tebere irrigation scheme, Kenya. A. arabiensis was the only member of the A. gambiae complex identified from chromosome characteristics. Other Anopheles species found included A. pharoensis Theobald, A. rufipes Gough and A. coustani Laveran. Survival rates gonotrophic cycle for A. arabiensis averaged 0.37 during the short rains (October-November), 0.49 during the dry season (February) and 0.78 during the long rains (May-June). Vectorial capacities were correspondingly low due to low survival rates and a high degree of zoophily. The average duration of infective life for P. falciparum was 0.2 days for both A. arabiensis and A. funestus. In contrast, entomological inoculation rates were comparatively high: 6-8 infective bites/man/month. A. pharoensis averaged 110 bits/man/night during the short rains; 1/999 (0.1%) was positve by ELISA for P. falciparum circumsporozoite antigen, but the ELISA evidence is not conclusive for vector incrimination. In correspondence with clinical observations, the transmission of P. malariae and P. ovale is unlikely due to the low vector survival rates. The observed anomaly between low vectorial capacities and high entomological inoculation rates demonstrates the importance of accurately estimating vector sporozoite rates to monitor unstable malaria transmission in irrigated areas.