Resistance to development of equine ehrlichial colitis in experimentally inoculated horses and ponies.

This research article investigates the development of resistance to equine ehrlichial colitis in horses and ponies after they were inoculated with Ehrlichia risticii twice.

Experiment Setup and Procedure

• For the study, fourteen ponies and three horses were selected as subjects and all of them were inoculated with Ehrlichia risticii. This species is the bacteria that can cause equine ehrlichial colitis, a severe diarrhea disease in horses.
• This was not the first time these animals were exposed to the bacteria. All of them had been inoculated with the same pathogen 2 to 20 months prior to the second one in the current study.

Findings After the First Inoculation

• Following the initial inoculation, all the seventeen animals presented clinical signs of equine ehrlichial colitis suggesting that the strain of Ehrlichia risticii used was virulent and managed to cause disease in all the subjects.
• Before the first inoculation, none of the horses and ponies had a detectable level of antibodies (to fight against Ehrlichia risticii) which further confirms that they were not exposed to this bacterium prior to the experiment.
• Once infected, all the subjects showed development of titers, indicative of the production of antibodies to combat the pathogen.

Findings After the Second Inoculation

• Unlike the first inoculation, this time, 16 of the 17 animals did not show any clinical signs of the disease, suggesting that they may have developed resistance to the infection caused by the bacterium.
• Only one pony showed clinical signs of having been affected by the bacteria- a transient fever and depression. However, the absence of colitis symptoms indicates that the severity was significantly reduced compared to the first inoculation.
• Interestingly, researchers found that most of the animals did not show a significant change in titer levels after the second inoculation. This might be because their immune system had already developed an adequate response to the pathogen during the first infection and thus, no extra antibodies were needed.

Implication of the Findings

• The research suggests that horses and ponies can develop resistance to Ehrlichia risticii and potentially prevent equine ehrlichial colitis upon repeated exposure to the bacterium.
• This study provides a rationale for further research in developing vaccines against this infection by targeting the immune response triggered upon infection.