Volume 32, Issue 2
  • ISSN: 0002-9637
  • E-ISSN: 1476-1645



St. Louis encephalitis (SLE) virus has continued to be active in the Colorado Desert region of Southern California (Coachella and Imperial Valleys) since 1973, while it has virtually disappeared from the Sacramento and San Joaquin Valleys of Central California. Consequently, comparative vector competence studies were undertaken from 1978 to 1981 to evaluate the susceptibility of populations of and from the San Joaquin and Coachella/Imperial Valleys to oral infection with representative SLE viral strains from each geographical area. females from both areas were equally susceptible to infection with both viral strains by the pledget and viremic chick feeding techniques. Although susceptibility profiles were similar by both feeding techniques, infection thresholds (i.e., IDs) obtained with females were at least 10,000-fold lower when fed on viremic chicks than on virus soaked pledgets. females from the two geographical areas were equally susceptible to infection with the indigenous viral strain by feeding on pledgets, and were uniformly more susceptible than sympatric populations of . Thus, differences observed in SLE viral activity in different geographical areas of California since 1973 cannot be explained by differences in the susceptibility of or to oral infection with SLE virus.


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