Detection ofSt.LouisEncephalitis VirusAntigen inMosquitoes by Capture EnzymeImmunoassay

pools ofinfected mosquitoes after 3handovernight incubation, respectively. Thesensitivity oftheprocedure was 90.5% inidentifying pools withinfectious titers >dex3.0.Thespecificity oftheassaywas controlled byretesting positive pools preincubated withSLEvirus andnormalantibodies, whichledtoadiminution ofsignal inthepools containing viral antigen. Theprocedure was suitably specific indiscriminating betweenSLE andrelated flaviviruses, detecting onlyhighinfectious dosesofheterologous antigens. St.Louisencephalitis (SLE)isthemostimportant cause ofepidemic viral encephalitis inNorthAmerica(12; T.F. TsaiandT.P.Monath, inR.D.Feigen andJ.D.Cherry, ed.,Textbook ofPediatric Infectious Disease, inpress). Outbreaks, occurring principally inthecentral andeastern United States, ledtoover1,000 casesinthe1950sand1960s andover 2,000 casesinthe1970s(3,12). Thedecennial periodicity ofepidemic SLEsuggests thatmajoroutbreaks may yetoccurinthis decade (4,12). Novaccine or specific therapy isavailable forSLE,but preventative public health measures arepossible intheform ofmosquito control (2,13).Forthese measures tobe effective, surveillance forSLEvirus activity inadvance of its occurrenceinhumansiscritical. ThemeasuresofSLE virus activity innaturewhichbestpredict possible epidemic activity areserologic surveillance ofbirds andmonitoring numbers andinfection ratesinvectormosquitoes (2,13). Thestandard method fordetecting SLEvirus inmosquito pools isbyvirus isolation incell culture orinsuckling mice. Underoptimumconditions, isolation andidentification of SLEvirus inprimary duckembryocell culture requires 3to 5 days.Inthisstudy, we describe an antigen detection enzyme immunoassay (EIA)bywhichSLEvirus-infected mosquito pools could beidentified in5h.