THE INCIDENCE OF GASEOUS LYMPHADENITIS IN ALBERTA SHEEP AND ASSESSMENT OF IMPACT BY VACCINATION WITH COMMERCIAL AND EXPERIMENTAL VACCINES

In Alberta, caseous lymphadenitis (CLA) is one of the leading causes o f lamb and mutton carcass condemnation. In this study, serologic resul ts confirmed a high (50-94%) incidence of exposure to Corynebacterium pseudotuberculosis, the causative agent of CLA, in mature, unvaccinate d sheep in southern Alberta. To assess the efficacy and impact of vacc ination with 2 commercial (Glanvac-6 and Case-Vac) and 1 experimental (WC + MDP-GDP) CLA vaccines, a series of 3 field trials in 3249 ewes a nd lambs was conducted in affected flocks from 1992-1996. Efficacy was assessed from the serological response to vaccination, prevalence and size of injection site reactions by treatment, and the incidence of C LA abscesses. Overall, agglutinating antibody titres to C. pseudotuber culosis in lambs vaccinated with WC + MDP - GDP and Case-Vac remained significantly elevated above nonvaccinated control lambs for the 12 mo period after the initial vaccination. Lambs vaccinated with the WC MDP - GDP maintained higher titres (P < 0.06) than those vaccinated wi th Case-Vac for the period from 6 to 12 mo after vaccination. Agglutin ating antibody titres for lambs vaccinated with Glanvac did not differ from those of controls at any point during the 12 mo period after vac cination. The number of injection site reactions was elevated in lambs vaccinated with Glanvac as compared to those vaccinated with WC + MDP - GDP but the size of injection site reactions did not significantly differ. Sheep vaccinated with WC + MDP - GDP also had a reduced incide nce of putative CLA abscesses, although confirmation of the presence o f C. pseudotuberculosis was only successful in a small number of insta nces.