Evaluation of fetal infection and abortion in pregnant ponies experimentally infected with Ehrlichia risticii.

This research investigated the fetal infectivity of Ehrlichia risticii, a bacterium, in pregnant ponies, finding that the bacterium causes abortions and ill health in infected fetuses under experimental conditions.

Experimental Procedure

• 19 ponies were selected for this study, all of which were negatively tested for E. risticii in an indirect fluorescent antibody (IFA) test.
• Of these 19 ponies, 13 were infected with E. risticii between the 90th and 180th days of their gestation period, while the remaining 6 served as controls.
• Each infected pony eventually developed signs of equine monocytic ehrlichiosis, a horse disease caused by E. risticii, and IFA titer to E. risticii demonstrated their infection.
• Two infected ponies became recumbent, unresponsive to supportive care, and were, therefore, euthanized.
• The rest of the ponies were observed for any reproductive anomalies after they recovered from the disease.

Effect on Fetuses and Parturition

• Out of the infected ponies, six experienced abortion at an average gestation period of 217 days.
• Five fetuses from the aborted ponies were evaluated and E. risticii was found in four of them.
• These five fetuses all had similar pathological conditions like enterocolitis, periportal hepatitis, and lymphoid hyperplasia, indicating the deleterious effect of E. risticii.
• While all fetuses tested negative for E. risticii-IgG antibodies, three had low titers of IgM antibodies specific to E. risticii.
• The other five infected ponies gave birth normally, and the disease in their newborns was confirmed by an IFA test, with three out of four foals testing positive.
• The growth rate of the two foals infected at birth was found to be similar to the control foal, ruling out any long-term physiological effects on survivors.
• None of the control mares faced complications during parturition, adding further evidence to E. risticii’s impact on equine gestation.
• Interestingly, two control ponies seroconverted to E. risticii six weeks prior to birth, suggesting the possibility of natural infection.

Findings

• The research concluded that E. risticii is primarily an abortifacient bacterium, meaning it causes abortions upon infection during gestation.
• The pathological conditions observed in the fetuses and the infection detected in them establishes that E. risticii can infect fetuses in utero.