Antibody and skin-test responses of sheep vaccinated against Johne's Disease

Current vaccines against Mycobacterium avium subsp. paratuberculosis (MAP, Johne's Disease) may cause animals to react positively when tested for Mycobacterium bovis (Bovis). Therefore, the effects of vaccination on MAP serum Ab and skin-test responses to MAP and Bovis PPD were compared in 25 ewes vaccinated against MAP with 24 control ewes in an infected flock 3 years post-vaccination. MAP-specific Ab levels were higher (P < 0.001) in vaccinated ewes than in control ewes. All increases in skinfold-thickness from 0 to 48 h were greater (P < 0.0001) than zero while increases in skinfold-thickness from 48 to 72 h were greater (P < 0.05) than zero for Johnin but not for Bovis PPD. The Vaccine × PPD × Time interaction for skinfold-thickness was significant (P < 0.001) with greater increases to Johnin than to Bovis, but with much greater increases in vaccinated ewes. These data suggest that administration of vaccines against MAP developed from whole organisms increase the likelihood that animals will be classified as “responders” to a Bovis screening test and negative by the follow-up comparative cervical tuberculin test, but they also show that vaccination initiates both humoral and cell-mediated MAP-specific responses.