Identification of Ehrlichia risticii as the causative agent of two equine abortions following natural maternal infection.

The research investigates and confirms the role of Ehrlichia risticii, a bacterium, in causing abortions in horses following maternal infections. It’s an important study as it solidifies this bacterium as an agent that can disrupt equine pregnancies.

Introduction to the Study

• The research was conducted following cases of two pregnant mares (mare 1 and mare 2) diagnosed with equine monocytic ehrlichiosis – a bacterial illness in horses that is caused by Ehrlichia risticii.
• Both mares had a history and clinical signs of the disease and high serum antibody titers to Ehrlichia risticii, a type of bacteria.
• Despite recovery from the illness, both mares aborted at 203 and 226 days of gestation respectively.

Detailed Observation of Both Cases

• The fetuses from both mares were expelled in fresh condition, and both mares retained their placentas upon abortion.
• Visible abnormalities in the fetuses included meconium staining and petechiation (tiny flat red spots) of external surfaces.
• Examination of the fetuses’ internal structures indicated an increased volume of feces in the small and large intestines, and liver discoloration with enlargement.
• Microscopic investigation showed symptoms including lymphohistiocytic enterocolitis (an inflammatory bowel disease), hepatitis, and myocarditis (inflammation of the heart muscle), as well as lymphoid hyperplasia (excessive growth of cells) and depletion in the spleen, thymus, and lymph nodes.

Evidence of Ehrlichia risticii

• Ehrlichia risticii was found in various organs of the fetuses including bone marrow, spleen, lymph node, colon, and liver for the first fetus and bone marrow and colon for the second fetus.
• Under the electron microscope, the recovered organism displayed characteristics common to E. risticii.

Elements of Confirmation

• For further confirmation of the role of E. risticii in the observed manifestations, the researchers inoculated the bacterium into a naïve pony, which consequently developed high levels of antibodies against E. risticii, suffered ehrlichemia (presence of E.risticii in the blood), and displayed clinical signs such as depression, anorexia, and mild diarrhea.

Conclusion

• Through these findings, the research confirms that E. risticii causes abortion under conditions of natural infection and should be taken into consideration when diagnosing causes of equine abortions.