The transovarian passage of hemagglutination-inhibition (HI) antibodies to St. Louis encephalitis (SLE) virus was studied in 18 naturally infected hens and 51 of their chicks. HI antibody was readily detected in the 24-hour-old chick in quantitative relationship to maternal antibody titers. The loss of this inhibitor was an exponential function of time, and was below detectable levels at the 4th week.
Serum-neutralizing antibody studies on the hens indicated the SLE-HI inhibitor was specific antibody. In contrast, the Eastern encephalitis-HI inhibitor appeared to be a non-specific substance related to the ovulatory activity of the bird.
The interpretation of SLE-HI antibodies in chicks under 4 weeks of age requires consideration of the presence of maternal antibody as a contributing cause.
The authors are Director, Chief Serologist, Chief Biologist, and Statistician, respectively, of the Encephalitis Research Center, Florida State Board of Health, Tampa, Fla.