Effects of vaccination before or after M. a. subsp. paratuberculosis (Map) experimental infection in goats

Abstract

Previous field studies have pointed out that vaccination of adult animals, presumably already infected with Map, decreases the appearance of new clinical cases, suggesting a therapeutic effect. With the aim of investigating the effects of vaccination, a total of 35, 1.5 month-old goat kids were employed. Eight of them were vaccinated subcutaneously with 1ml of an inactivated vaccine (Silirum®), and one month later orally challenged with 1010 CFU of the Map K-10 strain. At the same time, 14 non-vaccinated kids were similarly infected. The rest of the animals were kept as vaccinated (5) or non vaccinated non infected (8) controls. The peripheral immune response was assessed by indirect ELISA and IFN-a release tests. At 150 days post-infection (dpi), 5 infected and 3 infected and vaccinated kids were pathologically examined. After lesion development verification, five already infected kids were vaccinated with the same product at 180 dpi. At 360 dpi all the animals were slaughtered. A significant increase in IFN-a production was detected in all the vaccinated animals 1 month post-vaccination, that was significantly lower in those vaccinated after the infection. At 150 dpi, granulomatous lesions were identified both in infected and in vaccinated-infected kids, but the number of granulomas were significantly higher in the former group. Moreover, in vaccinated-infected animals lesions were restricted to the lymphoid tissue (focal forms) and demarcated whereas in the unvaccinated group they were seen in the mucosa either related or not to the Peyer’s patches. Among kids slaughtered at 360 dpi, only one of those vaccinated prior to infection had lesions and these were only few focal granulomas whereas more severe lesions, and with no differences between groups, were found in those animals only infected or those vaccinated after the infection. According to these results, vaccination does not prevent infection but has a clear protective effect if administered before challenge; however, in most of the animals with an established infection, vaccination does not stop the progression of the lesions.