Persistence of rabies antibody in free-ranging raccoons.

The immune status of a wildlife population to rabies virus probably influences the occurrences of epizootics among that species in a given geographical area. This is not to say that enzootic transmission of the virus will not occur, but rather that attainment of epizootic levels may be hampered through herd immunity. After an epizootic of rabies in a raccoon population in the Fall of 1970, a serologic surveillance program was initiated from November 1970 through August 1974. The surveillance provided the opportunity to determine the persistence of antibody in individual animals as well as to compare the sensitivity of intracerebral mouse inoculation and the RFFIT. The average point prevalence of neutralizing antibody was 20.9% (range, 15.5% [1970] to 25.0% [1974]). Fifty-one (18%) of the 476 raccoons monitored during the study period were trapped more than once. The testing of sequential serum samples from individual seropositive raccoons indicated that serum neutralizing antibody can persist for at least 37 months. It cannot be stated with certainty that these antibody titers resulted from a single exposure to rabies virus and were not boosted by further experience with the virus. Serial serology tests on three young raccoons (less than 15, 30, and 52 weeks of age) suggest that endemic rabies virus was circulating in or near the study area between June 1972 and February 1974. Thirty-six raccoons trapped in November 1970 were shipped to the Centers for Disease Control, Lawrenceville, Ga, where they were held in captivity for observations and serologic monitoring.(ABSTRACT TRUNCATED AT 250 WORDS)