Development of a species-diagnostic polymerase chain reaction assay for the identification of Culex vectors of St. Louis encephalitis virus based on interspecies sequence variation in ribosomal DNA spacers.

Culex pipiens complex mosquitoes (Cx. p. pipiens and Cx. p. quinquefasciatus) are among the principal vectors of St. Louis encephalitis (SLE) virus in the eastern United States; Cx. restuans and Cx. salinarius play secondary roles in the transmission and maintenance of the virus cycle. Accurate identification of these three species in field collections is required for epidemiologic studies of SLE virus transmission. We have developed a polymerase chain reaction (PCR) assay for this purpose. Species-specific PCR primers were designed based on interspecies nucleic acid sequence variation in the first and second internal transcribed spacers (ITS1 and ITS2) of the nuclear ribosomal DNA gene array; however, insufficient variation was detected to differentiate between subspecies of the Cx. pipiens complex. The primers were used together in a single amplification reaction to correctly identify specimens to species using genomic DNA extracted from whole individual mosquitoes, DNA from triturated mosquito pools, or crude DNA from mosquito heads or legs.