Introduction

Paratuberculosis has a high prevalence in Argentina. Some regions of the country show seroprevalence between 2.5 to 51.5 %. The purpose of the present study was to evaluate the efficacy of different methods to detect paratuberculosis in dairy cattle herds in Argentina.

Materials and methods

Fifty-two cows were selected from a dairy herd in Argentina. Sera from the animals were analyzed by indirect ELISA, using Map protoplasmatic antigen. Nine recombinant antigens were used in IFN-γ assay, 3 of Map (Lpp24, P34 and Bacterioferritin) and 6 of M. bovis (ESAT-6, CFP-10, 2624, 3747, Tpx, Trbb). Responses to recombinant antigens and to aviar PPD were analyzed by an in vitro assay for IFN-γ (Bovigam). Faeces, milk and in-line milk filters culture, following decontamination with hexadecylpyridinium (0.75%w/v) for 24 h, were done in tubes containing Herrold's culture medium supplemented with mycobactin (2mg/L) and pyruvate (4g/L). Samples were also tested by IS900-PCR.

Results

The results showed that 45 out of 52 (86.5%) animals were positive to ELISA. Fourteen animals were culture positive in faeces (14 of 52, 27%). All the animals that excreted the bacteria through faeces were ELISA-positive. Only one of these animals was culture positive in milk. However we were able to isolate one colony from the in-line milk filter at farm level. Nine animals showed significant levels of IFN-γ with aviar PPD (9 of 52, 17%). All IFN-γ positive samples were ELISA-positives and faecal culture positives. Unfortunately, in the present study the use of recombinant antigens in IFN-γ assay did not enhance the specificity of the standard test using aviar PPD. We obtained negative PCR results in all samples.

Conclusion

In a control programme, an ELISA test would be a good first step for identifying the affected herd, following of culture of faeces