The efficacy of a killed vaccine against paratuberculosis in cattle has been assessed in a field study, using a histopathological method for the evaluation of paratuberculosis-associated lesions in culled animals. Based on previous natural and experimental studies, lesions present in the intestine and associated lymph nodes, were classified as focal-multifocal -related to initial or latent forms, low bacterial load and subclinical-, and diffuse or severe, usually with high levels of mycobacteria in the tissues.The study has been carried out in a Friesian dairy herd, showing approximately a 12% of annual clinical cases of the disease, and formed by 468 adult cows. A 75% of the total, regardless the age or clinical status, was vaccinated with a single dose of SILIRUM® (CZ Veterinaria) and the remaining 25% kept as unvaccinated controls. For a period of 30 months post-vaccination (mpv), all the culled animals, for any reason, have been recorded and pathological studies carried out in 79 of them. Cellular and humoral peripheral immune responses have been also assessed by IFN-γ production and ELISA tests respectively. Vaccination induced strong cellular and humoral responses that persisted in more than 90% of them until the end of the study. No new clinical cases appeared later than 6 mpv. The total number of culled animals (n=192), in the evaluated period, was higher in the control (48.1%) than in the vaccinated group (39%). A significant reduction in the percentage of culled animals that showed lesions associated with paratuberculosis infection has been also observed in vaccinated (56.6%) with respect to control (92.3%) cows. A clear decrease has been also observed in the number of cows with diffuse or severe lesions (15.1% of vaccinated vs 34.6% of controls) although some of them have appeared, at 30 mpv, in vaccinated cows. Vaccination has shown to be a valuable method for achieving a significant reduction of paratuberculosis in a herd with high percentage of losses.

Sponsorship

This work was founded by grant LE24/04 from Junta de Castilla y León.