Evaluation of a Live Paratuberculosis Vaccine in Endemically Infected Flocks of Sheep and Goats in Greece

Abstract

A large 7-year vaccination trial was conducted in 15 flocks of goats and 7 flocks of sheep, known to be infected with Mycobacterium avium subsp. paratuberculosis (MAP), in Northern Greece. A total of 3665 kids and 1685 lambs, 7-30 days old, were vaccinated during 1995-1999. Seven hundred and seventy-five kids and 413 lambs were kept as unvaccinated controls. For each trial, the Incidence Rate Ratio (IRR), with respective exact 95% confidence intervals, was calculated. All IRR point estimates for young animals were very large (from 5.68 to 11.78 for kids and from 4.28 to 10.08 for lambs), while none of the 95% confidence intervals included 1. The protective effect of vaccination was large and the difference in mortality among vaccinated and unvaccinated animals was more pronounced in young animals. The effect in adult animals was smaller than in young animals; it was, however, still considerable. Upon visual inspection of the K-M curves, it seems that for the young animal trials the vaccinated and control-group curves were diverging increasingly over time, which indicates that the gain from the vaccination (or the loss from non-vaccination) might increase over time during the trial.