A total of 287 sera collected from children under 15 years (104) and adults residing in eight communities in Monagas State, Venezuela, was examined for presence of antibodies to arthropodborne viruses by hemagglutination-inhibition and neutralization tests.
No immunity to eastern and western equine encephalitis viruses was encountered, but, with the exception of Maturín, each community had some adults who were immune to Venezuelan equine encephalitis virus. Only three sera from adults were found to neutralize Mayaro. No evidence of recent activity of yellow fever and dengue type 2 viruses was discovered. Eight sera neutralized Ilhéus but no other group B agent used, and two sera neutralized St. Louis encephalitis virus only. Neutralization test results with a Caraparu-like agent, TRVL 34053-1, indicate that infections with this or a closely related agent have occurred occasionally. In each community there were some sera that neutralized Cache Valley virus. Limited tests with a Manzanilla antigen gave negative results.