Transmission of St. Louis Encephalitis Virus from Argentina by Mosquitoes of the Culex Pipiens (Diptera: Culicidae) Complex

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Abstract
St. Louis encephalitis (SLE) virus transmission cycles in tropical America and temperate South America are poorly defined. Elucidation of these cycles may help to explain basic differences between these areas and temperate North America with regard to disease incidence and severity of clinical illness due to SLE virus. Results of the first experimental studies on the virus-vector relationships of a SLE viral strain and a mosquito strain from Argentina are presented. A mosquito strain and a SLE viral strain from temperate North America were also included in the study in order to have a basis for comparison. Colony strains of Culex pipiens quinquefasciatus from Esperanza, Santa Fe Province, Argentina, and Cx. pipiens complex mosquitoes from Memphis, Tennessee, USA, were fed on chicks infected with either of 2 SLE viral strains from Esperanza and Dayton, Ohio, USA. On the 20th day of extrinsic incubation, 100% of the Argentina mosquitoes were infected irrespective of the viral strain used. A high proportion of Memphis mosquitoes became infected (87.8% and 89.8%), but they were less efficient in transmitting virus than their Argentina counterparts (58.3% vs. 90.0% Ohio SLE virus, and 40.0% vs 90.5% Argentina SLE virus). These differences may be due, at least in part, to the fact that the Memphis mosquitoes had fed on viremic chicks circulating less virus. Our results indicate that the strain of Cx. p. quinquefasciatus from Argentina is a very efficient vector of SLE virus under experimental conditions, and that the SLE viral strain from Argentina does not differ markedly from a temperate North American strain in its ability to infect and be transmitted by members of the Cx. pipiens complex.

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