Transmission of Rift Valley fever virus by different geographic strains of Culex pipiens in Egypt.

Previous investigations have delt with colonized Cx. pipiens and RVF virus interactions. This study evaluated the vector competence of parental Cx. pipiens populations for RVF virus and investigated variations in the vector competence among different geographic strains of this mosquito in Egypt. Cx. pipiens females were fed on viremic hamsters circulating 9.4-10.5 log10 SMICLD50 of virus. Mosquito samples were freezed at different intervals extending between 0-12 days of extrinsic incubation (EI). Transmission experiments started at day 5 of EI when individual females were allowed to refeed on normal hamsters. The infection rates for the geographic strains tested ranged between 85% and 100% and the transmission rates ranged between 6% and 35%. Transmission of RVF virus to normal hamsters took place at days 9, 12, 15 and 18 of EI by the different tested Cx. pipiens strains. Transmitter females contained significantly more virus than the non-transmitters except for the strain of Giza. Most of the infected Cx. pipiens individuals were of the non-transmitting type even those with high titers. Barriers at the salivary gland level competing RVF virus transmission are probably present in Egyptian Cx. pipiens. RVG virus infection was observed to adversely affect Cx. pipiens. The present investigation revealed no geographic variations in the vector competence of Egyptian Cx. pipiens for RVF virus.