COMPARISON OF THE ABILITIES OF SEROLOGIC TESTS TO DETECT PSEUDORABIES-INFECTED PIGS DURING THE LATENT PHASE OF INFECTION

Objective-To compare the sensitivities of all available serologic test s in detecting pseudorabies virus (PRV) antibodies in pigs during long -term latent pseudorabies. Design-Pigs experimentally infected with a virulent strain of PRV were maintained for 2 to 27 months after inocul ation. At the time of necropsy of each pig, blood was collected for se rologic evaluation, and tissues were obtained for polymerase chain rea ction (PCR) verification of latency. Animals-65 crossbred pigs each we ighing approximately 18 kg at the start of the study. Procedure-Serum samples from each pig were analyzed by serum neutralization, latex agg lutination, screening ELISA, particle concentration fluorescence immun oassay, automated latex agglutination, and differential ELISA for glyc oproteins I, ill, and X. DNA was extracted from the trigeminal ganglia and tonsils of each pig and was analyzed by PCR for PRV genomic seque nces. Results-PCR analysis of trigeminal ganglia and tonsils indicated that all pigs were latently infected with PRV at the time of necropsy , and serologic testing verified that ail pigs had PRV-specific antibo dies, regardless of duration of infection. The screening tests were vi rtually equivalent in sensitivity for detection of PRV antibodies. Of the differential serologic tests, the glycoprotein-l and -III marker s ystems, which performed with similar sensitivity as the screening test s, were superior to the glycoprotein-X marker system in detecting PRV antibodies in latently infected pigs Conclusion-Serologic testing cons istently detects pigs in the latent phase of PRV infection, provided t hat the test detects the antibody response to the whole virus or to a reliable PRV-marker glycoprotein.