Pseudorabies: experimental studies in raccoons with different virus strains

Raccoons (Procyon lotor) were infected by the nasal/oral route with as little as 10(2) plaque forming units (PFU) of pseudorabies virus (PrV). There was no apparent difference in the susceptibility of raccoons to infection with either of two virulent field strains or with the naturally avirulent K strain which has been used in modified live virus vaccines. Each of these three viruses was transmitted by contact to uninfected raccoons. All raccoons that were infected with virulent field strains died; however only two of 11 (18%) raccoons that were infected with the K strain died. One of four raccoons that survived infection with the K strain survived superinfection with virulent virus. This finding was significant because it could be a mechanism by which virulent PrV can be introduced and persist in the raccoon population. The possibility of this event occurring is increasing because of the widespread prevalence of PrV and the use of modified live virus vaccines for controlling clinical pseudorabies in swine. Virus neutralizing activity was found in five of 47 serums collected from raccoons that were trapped in PrV endemic areas. This observation implies that a herpesvirus, possibly PrV, may be present in the wild raccoon population.