Susceptibility of horses to Mycobacterium paratuberculosis.

This research examined the susceptibility of young horses, or colts, to a bacterium known as Mycobacterium paratuberculosis, which causes a chronic intestinal disease and it showed that horses could fall ill if exposed to the bacteria directly through the bloodstream or the digestive tract, or even indirectly through contact with infected horses.

Research Design and Method

• A total of eight colts were used in the experiment, with differing methods of exposure to the bacteria M. paratuberculosis.
• Two colts were introduced to the bacteria intravenously, and one colt was used as a contact control, meaning it was kept in close proximity with the infected colts but not directly exposed.
• Two other colts were exposed to the bacteria intragastrically, meaning the bacteria was introduced into their stomachs.
• One colt was administered killed M. paratuberculosis intravenously to see if the deactivated bacteria would provoke a response, and the last two colts were kept completely separate and unexposed to serve as normal controls.

Study Findings

• The colts that were administered live bacteria intravenously began losing weight 84 days after the exposure. These colts displayed clinical signs of disease that included loss of body weight and a rough coat.
• The infected colts also began to excrete M. paratuberculosis in their feces, indicating that the bacteria had established an infection in their intestinal tract.
• All the colts were euthanized for observation approximately 120 days after their initial exposure. Investigation of their tissue revealed inflammation in the small intestine and mesenteric lymph nodes, with the M. paratuberculosis bacteria often being found in the small intestine.

Diagnostic Limitations

• Importantly, the scientists also found that certain tests used to diagnose the infection, such as complement-fixation tests and intradermal johnin tests, had limited value. This suggests that these methods may not be effective in diagnosing M. paratuberculosis infection in horses.

Conclusion

• The results of the research confirm that, under the conditions of the experiment, horses are susceptible to M. paratuberculosis infection, which can lead to significant weight loss and other health problems.