Introduction

Bovine paratuberculosis is caused by infection of young calves with Mycobacterium avium subsp. paratuberculosis (MAP), and results in chronic granulomatous infection of the ileum. The aim of the present study was to perform a longitudinal follow up of immunological and microbiological parameters of calves experimentally infected in the first month of life.

Materials and methods

Twenty experimentally infected calves were sampled monthly during 4.5 years. The PBMC were isolated, and phenotyped by flow cytometry using a panel of 8 monoclonal antibodies. Lymphocyte proliferation assays, with a panel of 6 mycobacterial antigens were used for evaluating T cell function. Antibody responses were measured using ELISA coated with MAP PPD antigen, recombinant MAP heat shock protein of 65 kD, and 70 kD. Fecal culture was performed monthly to acquire data on the mycobacterial shedding.

Results

The results showed that based on fecal excretion patterns animals could be divided in three groups, one which is characterized by high frequent shedding (HFS), a group characterized by low frequent shedding (LFS) and an intermediate group (IM). Animals in the HFS group typically had lower cell mediated responses, especially during early stages of infection, when compared to animals from the LFS group. Conversely the HFS animals had early onset and higher antibody responses when compared to LFS animals.

Conclusion

Based on fecal shedding patterns we identified different host response patterns to paratuberculosis infection. Whether these different response patterns reflect successful or failing immune responses remains to be established as neither LFS nor HFS animals in the study developed overt signs of clinical paratuberculosis in the 4.5 years of the study. The HFS animals likely contribute significantly more to spread of the infection in the population. Host genetic make up could explain the observed response patterns and as such is subject of ongoing follow-up studies.