Vaccination against Johne's disease in sheep

Drs. Sue Stehman and Mary Smith, Population Medicine & Diagnostic Science, College of Veterinary Medicine and Dr. Mike Thonney, Department of Animal Science, College of Agriculture and Life Sciences

The goal of this project was to determine if Mycopar^®, a vaccine against Johne's Disease in cattle, is effective in preventing infection in sheep. Based upon sheep vaccination trials over the past 70 years, it was highly likely to be effective but no test of this vaccine had been carried out in sheep.

Johne's Disease is caused by the bacterium, Mycobacterium avium subsp. paratuberculosis. It is a progressive wasting disease characterized by bacterial invasion of the intestinal mucosa and associated lymph glands that does not induce the animal to make a sufficient immunological response. Young animals are particularly susceptible to infection but may not exhibit clinical disease until years later. The Cornell commercial Finn x Dorset flock was identified by Drs. Sue Stehman and Mary Smith as significantly infected so it is an ideal flock to study efficacy of vaccination. Although management strategies identified to control the disease in dairy cow herds have been tried, the nature of sheep flock management means that those management strategies are unlikely to be effective. Thus, demonstration of the efficacy of vaccination in sheep could lead to commercial acceptance of vaccination and have significant impact on the sheep industry.

Finn x Dorset replacement ewes born in the Cornell flock were used in this study. Over a two-year period beginning in 1999, 135 ewe lambs were vaccinated and another 125 contemporary ewe lambs were kept as controls. They were kept in the production flock until sampled or removed for lack of reproduction, or other usual culling reasons. About one-fourth of the control and vaccinated ewes were slaughtered after the first lambing after they are two, three, four, or five years of age. The intestinal tracts from these ewes and from ewes dying for other reasons were examined by histopathology to determine if the animals were infected by the Johne's Disease bacterium. Blood and fecal samples were obtained to attempt to monitor the disease incidence through serology and culture of the bacterium. Weights, lamb weaning weights, and reproductive data from the two groups were also obtained.

Only 14.1% of control animals that died or were slaughtered purposefully for sampling had evidence of infection by histopathology. Even with this relatively low control-animal infection rate, the P-value of 0.013 indicated that vaccination reduced infection. Among animals that were purposely sampled, the infection rates were 15.1 and 3.2% for control and vaccinated animals (P = 0.041), respectively. Based upon the histopathology results in this experiment, Mycopar^® is a promising vaccine to help control and eventually to eradicate Johne’s Disease from sheep flocks. The preliminary report is available in a PDF file for downloading.

The New York State Department of Agriculture and Markets and the Cornell Agricultural Experiment Station provided funding for part of this work.