[Ecology of leishmaniasis in the south of France. 21. Influence of temperature on the development of Leishmania infantum Nicolle, 1908 in Phlebotomus ariasi Tonnoir, 1921. Experimental study].

The influence of temperature on the life-cycle of Leishmania infantum Nicolle, 1908 (isolated from a dog in the Cévennes) in a known vector (Phlebotomus ariasi Tonnoir, 1921) was studied with special reference to the proportion of flies infected and the intensity and localization of parasites in the sandfly. Wild female sandflies were caught at night by active searches and were put with a heavily infected dog in a mosquito net on the night of capture. On the following morning, engorged females were tubed individually and were then maintained at 10, 15, 20, or 25 degrees C (+/- 1.5 degrees). The temperatures were chosen after preliminary experiments which showed that temperatures of 30 degrees C or less than 5 degrees C were lethal to both the sandfly and, usually, the parasite. Midguts of the flies were dissected and examined 6 to 10 days after the infective feed. Although there were no obvious differences in the proportions of infected sandflies at different temperatures, a statistical analysis of the finding (chi 2 test) showed that raising the temperature: significantly increased the overall proportion of infected sandflies; speeded up the multiplication of promastigotes in the midgut; controlled the movement of parasites forwards into the thoracic midgut (from 15 degrees C); encouraged the attachment of the flagellates to the wall of the stomodaeal valve (from 20 degrees C). The use of an exponential model to deduce the size of the parasite population at the different temperatures led to the conclusion that the optimum temperature for L. infantum is in the region of 25 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)