EXPERIMENTAL INFECTION WITH Mycobacterium avium subespecies paratuberculosis OF CALVES PREVIOUSLY IMMUNIZED

M MUÑOZ, A VERNA, O MORENO, C GARCÍA-PARIENTE, L E REYES, J BENAVIDES, M FUERTES, M C FERRERAS, J F GARCÍA MARÍN, V PÉREZ.

Casa das Artes de Vila Nova de Famalicao. Portugal

Congreso; 12th Annual Meeting of the Portuguese Society of Animal Pathology with 16th Annual Meeting of the Spanish Society of Veterinary Pathology; 2004

  Paratuberculosis is an infectious disease of ruminants caused by Mycobacterium avium subespecies paratuberculosis (Map) that occurs frequently all over Spain. In bovine species, a classification of the lesions associated with natural paratuberculosis, showing not been validated in an experimental model. On the other hand, in sheep it is well known that vaccination, considered as the most efficient method for controlling the disease, does not prevent the infection but modifies the progression of lesions towards focal and latent forms. This fact has not been studied in cattle. Whit the aim of elucidate these topics, and experimental infection has been carried out using 18 Frisian calves, orally challenged with map when 5 months old, after their immunization with a killed vaccine (Silirum®) two months earlier. The following groups were considered: i) Infected and non-vaccinated (n=6) (INV); ii) Infected and vaccinated (n=8) (IV); iii) Non-infected and vaccinated (n=2) (NIV); iv) Non-infected and non-vaccinated (n=2) (NINV). At 180 dpv (120 dpi) 5 calves were sacrificed (3 from IV and 2 from INV groups). The remaining animals were killed at 330 dpv (270 dpi). In all the cases a complete histopathological study  were carried out,  focusing on the intestine  associated lymphoid tissue. Humoral and cellular peripheral immune responses were assessed at different periods along the study, as well as the detection of Map DNA in blood samples by PCR. The histopathological study confirmed the pathological classification proposed in natural cases. Focal lesions, located mainly in the lymph nodes, and multifocal an diffuse forms, harbouring higher numbers of gigant cells than in sheep, were described. Concerning type of lesions according to the treatments received, in calves from group IV they were absent or focal or absent, except for one case having diffuse forms. However, in INV group, lesions varied from multifocal to diffuse, associated with high number of bacilli. Control animals did not show any lesion. These results suggest that vaccination in cattle does not prevent the infection but induces a high number of animals having focal or latent lesions, with respect to non- vaccinated animals. However, protection is not absolute since a vaccinated calf had severe lesions.