A protozoan parasite could be a significant cause of abortion in horses, the findings of fresh research suggest.
Neospora can infect a wide range of domestic and wild animals, causing a disease known as neosporosis.
Neosporosis is recognized as one of the major causes of abortion in cattle worldwide. Neospora caninum has been found to be highly efficiently at crossing the placenta into fetuses, and it is generally accepted that transplacental transmission is the major route of transmission in cattle.
In horses, Neospora caninum has been associated with fetal loss and Neospora hughesi has been linked with neurological disease.
Monica Leszkowicz Mazuz and her fellow researchers, in a study just published in the journal Pathogens, set out to investigate the role of Neospora infections in equine abortion in Israel.
The presence of anti-Neospora antibodies was evaluated in 31 mares who aborted. The presence of parasite DNA in their aborted fetuses was also evaluated.
The seroprevalence in aborting mares was found to be 70.9% and the prevalence by DNA detection in the aborted fetuses was 41.9%.
Transplacental transmission from positive mares to their fetuses was 45.4%, while 33.3% of fetuses from seronegative mares also tested positive for Neospora.
Positive samples were identified by sequence analyses as N. caninum in all the mares involved in the study.
“These findings suggest that N. caninum could be a significant cause of abortion in horses and that transplacental transmission in horses is an important way of transmission of N. caninum,” the study team reported.
“Therefore, in neosporosis endemic areas, it is important to include Neospora as a possible cause of abortion in mares.”
The results, they said, show the necessity to use several tests together, both serological and molecular, to confirm the involvement of Neospora in equine abortions.
Discussing their findings, the study team said the seroprevalence found in the population of aborting mares in the study, at 70.9%, was high — higher than in other surveys of healthy horses, which reported prevalence ranging from 0% to 63.6%.
Several other surveys had demonstrated high seroprevalence in pregnant or aborting mares (up to 85%), they noted.
Most abortions in their study had occurred in late pregnancy, they noted.
“This concurs with a previous report linking the presence of Neospora DNA in fetuses to late-term abortion or stillborn foals.”
Differing from cattle, where high concentrations of antibodies had been associated with abortion, in this study aborting mares presented relatively low levels.
Two Neospora species have been classified to date. N. caninum was first classified in 1988, and since then, it has been reported in a large variety of mammal species.
N. hughesi was first identified in 1998 and has been described only in horses. Horses, they said, may potentially be infected with both species. While N. hughesi has been linked to neurological disease in horses, its role in equine abortion is obscure.
They said the impact of Neospora infection on the development of the fetuses and the mechanism by which it might induce abortion is still not fully determined in horses. More work is needed in this area, they said.
“Overall, the findings presented here emphasize the potential role of Neospora infection in equine abortions, showing efficient transplacental transmission to fetuses in both seropositive and seronegative mares.
“As Neospora infection was present also in fetuses from seronegative mares, exclusion of neosporosis as a cause of abortion should include not only the serological status of the mare but also testing for the presence of Neospora species DNA in the aborted fetus.”
The study team comprised Leszkowicz Mazuz, Sharon Tirosh-Levy, Nir Edery and Shlomo Blum, all with the Kimron Veterinary Institute in Israel; Lea Mimoun, Gili Schvartz, Gad Baneth, Igor Savitzki and Amir Steinman, with The Hebrew University of Jerusalem; and Nicola Pusterla, with the University of California, Davis.
Leszkowicz Mazuz, M.; Mimoun, L.; Schvartz, G.; Tirosh-Levy, S.; Savitzki, I.; Edery, N.; Blum, S.E.; Baneth, G.; Pusterla, N.; Steinman, A. Detection of Neospora caninum Infection in Aborted Equine Fetuses in Israel. Pathogens 2020, 9, 962.