The development of Aujeszky's disease diagnosis in Thailand

Three diagnostic techniques, viral isolation (VI), DNA hybridization (DH) and immunofluorescence (IF) for identifying pigs infected with the CB-1 strain of Aujeszky's disease (AD) virus were evaluated using samples collected form five experimentally infected animals. All Techniques detected infection in the tonsil and olfactory bulbs from 3 to 9 days after infection. The DH technique was the most sensitive detecting 21 samples while IF detected 19 and VI demonstrated infection in 13. A DNA probe derived from the Pst 1 fragment of the Phylaxia European strain of AD was used to detect the Bam HI fragments of the CB-1 and NP-1 Thai strains of AD. The Bam HI fragments of these strains migrated at a significantly different rate to the reference European strain suggesting that this technique could be used to differentiate Thai and European strains of AD. A quantitative indirect ELISA used to measure immune responses following vaccination with AD was compared with virus neutralization (VN) test. There was an agreement of 88.4% with 48 and 76 ELISA units corresponding with VN titres of 4 and 16 respectively. Surveys of the seroprevalence of AD in 15 commercial herds were carried out using a commercially available indirect ELISA based on an affinity purified gI antigen and a blocking ELISA utilizing a single monoclonal antibody which reacts with the gI glycoprotein. There was 100% agreement in samples collected from 13 herds and 93% for the 2 remaining herds. There was one herd having no reactors. While four herds with a prevalence of 2.1 to 15.6% are candidates for vaccination with removal of infected animals, the remaining 10 herds (71%) had a prevalence of >20% indicating that removal of infected animals is not a viable option until the prevalence of infection can be reduced. (author). 21 refs, 3 figs, 5 tabs