Johne’s disease is a chronic enteritis associated with ruminants caused by the intracellular pathogen Mycobacterium avium subsp. paratuberculosis (MAP). MAP is a highly prevalent and costly disease worldwide in large and small ruminant species, such as cattle, sheep, and goats. In the US, it is estimated that over 90% of dairy herds are infected with MAP. The clinical signs are characterized by chronic diarrhea with body weight loss in the later stages of infection. It has been shown that the subclinical stages of MAP were associated with decreased milk yield and higher risk for other common production diseases due to body weight loss and debilitating immune response. Infected animals with MAP are difficult to identify and segregate from the herd or flock due to: (1) long incubation period (it could take years), (2) the absence of clinical signs until advanced stages, and (3) the lack of reliable diagnostic methods. Newborn animals are infected at the time of parturition by ingesting MAP via colostrum and milk as well as environmental exposure to MAP in manure from infected cows. Identification of MAP in feces is performed by culture or PCR, or sometimes by serum ELISA to identify antibodies against MAP. Although these testing methods are rapid and cost-effective, the efficacy of MAP detection is almost entirely dependent on the immune status of the host.
Vaccination is recognized as an effective method to prevent infections in livestock. There are a few commercially available vaccines for Johne’s disease worldwide (e.g., Gudair, Silirium); however, in the US, Mycopar® was the only USDA-licensed vaccine available for use (discontinued in the US in 2019). Its use was restricted to cattle, and only under the supervision of a licensed veterinarian. The increasing prevalence of MAP requires new efficacious vaccines as an essential management tool to control MAP. A recent study assessed the effectiveness of pooled MAP recombinant proteins as a potential vaccine. Two separate studies were carried out: 1) In the first study, vaccinated two-week old calves were immunized with a total of 400 µg protein cocktail per dose and 2) the second study compared doses of 400 µg versus 800 µg of protein cocktail using another set of two-week old calves. Calves were vaccinated twice 14 days apart starting at two weeks of age, then vaccinated and nonvaccinated control calves were inoculated orally three times with live MAP isolated from infected cows. At the end of 12 months study period, the authors showed that vaccinated animals had significantly reduced tissue colonization with MAP compared to control animals. Calves immunized with the higher dose had improved protection with reduced MAP burden. Furthermore, there was a negligible level of cross-reactivity between M. avium and M. bovis antigens, suggesting that infection could be differentiated from vaccinated animals when using serology assays. The authors concluded that vaccination of calves with the pooled four recombinant MAP proteins was efficacious in reducing tissue colonization and fecal shedding. Although experimentally, this novel vaccine has the potential to prevent or reduce the spread of Johne’s disease in cattle.
This study was conducted at the USDA-ARS, National Animal Disease Center located in Ames, IA. Please find below the reference for additional details:
Stabel, J.R., and J.P. Bannantine. 2021. Reduced tissue colonization of Mycobacterium avium subsp. paratuberculosis in neonatal calves vaccinated with a cocktail of recombinant proteins. Vaccine 39:3131–3140.