Western Equine and St. Louis Encephalitis Viruses in the Blood of Experimentally Infected Wild Birds and Epidemiological Implications of Findings

摘要

Several species of wild birds from Kern County, California were inoculated subcutaneously with high dilutions of western equine and St. Louis viruses. This frequently resulted in readily detectable viremia beginning within 24 hours after inoculation. With the western equine virus, viremia attained titers up to 10?6 and lasted 3 to 4 days. Antibody developed within 15 to 29 days following inoculation in all those adequately tested. Birds inoculated with St. Louis virus developed much lower titers of viremia, usually detectable only in the undiluted and the 10?1 dilution and only once detected at a level of 10?4. These titers are comparable to those found previously in domestic fowls, and mosquitoes had become infected in repeated instances following feedings made on these fowl. The inoculated birds in these experiments did not always develop neutralizing antibodies during the interval which had proved adequate for the western equine virus. One bird with demonstrated viremia had failed to develop detectable antibodies 30 days after inoculation. It is concluded from these experiments and other observations that in Kern County, California wild birds are as important as and probably more important than domestic fowl as sources of virus infection for mosquitoes.