Comparison oftheReactivities ofBaculovirus-Expressed Recombinant Norwalk VirusCapsid Antigen withThose oftheNative Norwalk VirusAntigen inSerologic AssaysandSomeEpidemiologic Observations

fecal material frominfected volunteers asthesource of antigen because ithasnotbeenpossible topropagate this virus incell culture. However, therecentcloning of the NV (strain 8FlIa) genome andexpression ofthecapsid protein inabaculovirus systemtoform"virus-like particles" hasprovided aconsistent sourceofantigen (designated rNV).Thepurposeofthepresent study was tocomparetheantigenicities ofthese rNV particles withthose ofnative NV antigen derived fromhumanfecal material byusing well-characterized seraobtained fromearlier studies. InIEM studies, therNV antigen reacted withNV-specific antibodies ina manner similar tothatobserved previously whenparticle-positive fecal material was usedasantigen. Inaddition, a direct enzyme-linked immunosorbent assay,inwhichtherNV antigen was usedas antigen, provedefficient andspecific forthedetection ofserologic responses toNV compared withthepreviously established techniques ofIEMandblocking antibody immunoassays inwhich particle-positive fecal material was usedastheantigen. Theavailability ofan unlimited sourceofantigen will enable serologic studies thatwill greatly increase ourunderstanding oftheepidemiology ofNV anditsrolein humanenteric illness. Norwalkvirus(NV),considered a memberoftheCaliciviridae family, hasbeenidentified as an important etiologic agentofacuteepidemic gastroenteritis, beingassociated primarily withoutbreaks inadults, school-age children, and family contacts(16). The27-nmvirus was identified by immuneelectron microscopy (IEM)in1972(19)infecal material derived froma 1968outbreak ofgastroenteritis in Norwalk, Ohio(1).Subsequently, othermorphologically similar viruses were associated withoutbreaks ofgastroenteritis andwere characteristically