Ambient temperature effects on the extrinsic incubation period of Wuchereria bancrofti in Aedes polynesiensis : implications for filariasis transmission dynamics and distribution in French Polynesia

Abstract

Temperature effects on development of the human filarial parasite #Wuchereria bancrofti (Cobbold) (Filaridea : Onchocercidae) in the main Pacific vector #Aedes polynesiensis Marks (Diptera : Culicidae) are analysed in relation to ambient climatic conditions. A statistical model of the extrinsic cycle duration as a function of temperature is described and used to distinguish three patterns of #W. bancrofti transmission dynamics : continuous, fluctuating and discontinuous, occurring from north to south geographically among French Polynesian archipelagos. In the northerly Marquesas Islands (8-11° S) filariasis transmission is continuous and very active, facilitated by perennially high temperatures combined with constantly high rates of man-vector contact. In the southerly Australes Islands (21-28° S) filariasis transmission is seasonally discontinuous and, during the cooler months (May-September), the model predicts virtually no transmission because the cycle duration exceeds the life expectancy of the vector. In the Society Islands (16-18° S), between the Marquesas and Australes, transmission is predicted to be intermediate as expected from their latitude, with seasonally fluctuating transmission potential. In the Tuamotu Islands (also geographically intermediate : 14-23° S), with theoretically perennial transmission potential, transmission occurs only intermittently, being limited by other human and environmental factors whereby man-vector contact is confined to seasonal agricultural situations. Generally, among French Polynesian archipelagos where #Aedes polynesiensis is the vector, the transmission potential for #W. bancrofti$ and resulting disease manifestations of lymphatic filariasis in humans are correlated with ambient temperature due to the degree of southern latitude. (Résumé d'auteur