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 tests 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 inoculation. At the time of necropsy of each pig, blood was collected for serologic evaluation, and tissues were obtained for polymerase chain reaction (PCR) verification of latency.

ANIMALS

65 crossbred pigs each weighing approximately 18 kg at the start of the study.

PROCEDURE

Serum samples from each pig were analyzed by serum neutralization, latex agglutination, screening ELISA, particle concentration fluorescence immunoassay, automated latex agglutination, and differential ELISA for glycoproteins I, III, and X. DNA was extracted from the trigeminal ganglia and tonsils of each pig and was analyzed by PCR for PRV genomic sequences.

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 all pigs had PRV-specific antibodies, regardless of duration of infection. The screening tests were virtually equivalent in sensitivity for detection of PRV antibodies. Of the differential serologic tests, the glycoprotein-I and -III marker systems, which performed with similar sensitivity as screening tests, were superior to the glycoprotein-X marker system in detecting PRV antibodies in latently infected pigs.

CONCLUSION

Serologic testing consistently detects pigs in the latent phase of PRV infection, provided that the test detects the antibody response to the whole virus or to a reliable PRV-marker glycoprotein.