Z-003. Oral Distribution of Pseudorabies Viral DNA in Feral Swine

E. C. Hahn, III, B. A. Fadl-Alla;
Univ. of Illinois, Urbana, IL.

Pseudorabies virus (PRV) has been eradicated from all domestic swine in the US, but remains endemic in most feral (wild) pigs. Risk exists that this herpesvirus in the feral swine reservoir can be transmitted to domestic pigs with severe economic and trade consequences. Studies on transmission from feral swine have focused on venereal mechanisms but the virus can also be found in the oral cavity. To determine the extent and distribution of oral infection in feral swine, various tissues from hunted feral pig heads were assayed for viral DNA by PCR using primers to amplify the gene for glycoprotein gC. Each tissue sample was separately dissected with new instruments to minimize viral DNA cross-contamination. Surprisingly, the virus was distributed widely among tissues, but not uniformly within tissues. As expected, strongest amplification was found in trigeminal ganglia and tonsils, but also in submandibular lymph nodes (SMLN). Moderate signals were found in cheek mucosa near the tusks, parotid and mandibular salivary glands, and circumvallate papillae. Since PRV circulating in feral pigs can be genotyped by gC DNA sequence analysis, it was possible to try to relate genotype with tissue distribution in feral pig heads. Neither frequency nor distribution of virus-positive sites correlated with genetic sequence within gC. In one comparison of triplicate tonsil and SMLN probes from 31 field samples, no statistical correlation was found between the number of positives in the two tissues (Pearson coefficient = .043; R2 = .003). Overall 84% of tonsil samples were positive; 67% of SMLN samples were positive. However, in no case were all triplicate samples from any tissue all positive. Conclusions drawn from these studies are (1) that distribution of viral DNA among feral pig oral tissues is common but non-uniform, (2) tissues are not uniformly infected and (3) that oral distribution could not be related to viral genetic differences, at least with gC. In terms of risk of transmission to domestic swine, oral transmission is highly probable.