Mycobacterial infection linked to 10 abortions in horses in Japan

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Mycobacterial infections are generally uncommon in horses.
Mycobacterial infections are generally uncommon in horses. Photo by sniggie

Researchers have linked 10 equine abortions in Japan to mycobacterial infections.

The cases, on seven Thoroughbred horse farms in the Hidaka district of Hokkaido, were caused by Mycobacterium avium subsp. hominissuis, the study team reported.

Yuta Kinoshita, Mari Takechi and their colleagues, writing in the journal Veterinary Medicine and Science, said bacterial placentitis in horses commonly results in abortion, premature birth or compromised neonatal foal health. However, mycobacterial infections are generally uncommon in horses.

The cases in question occurred between 2018 and 2019 in Japan. Direct contact among the mares on the seven farms was not recorded.

Most cases were characterized by extensive pathological lesions of the placenta, which are not typical in cases of common pathogenic bacteria such as Streptococcus zooepidemicus and Escherichia coli.

All abortions featured a white-yellow exudate on the surface of the placenta.

Mycobacterial granuloma formations could be seen under the microscope in the placenta and fetal organs, and bacterial samples were isolated from the placenta and fetal samples (the heart, lung, liver, kidney, spleen and stomach contents), or uterine lavage fluid.

The greatest number of bacteria was isolated from necrotic lesions on the placenta, which could be an important site for bacterial isolation in mycobacterial equine abortions.

The isolates were identified as Mycobacterium avium subsp. hominissuis based on genetic testing.

The strains in all cases were identical, suggesting the horses had been infected by the same unknown contagious source.

The study team comprised Yuta Kinoshita, Eri Uchida‐Fujii, Toshio Nukada and Hidekazu Niwa, all with the Japan Racing Association; and Mari Takechi and Kunio Miyazawa, both with the Hokkaido Hidaka Livestock Hygiene Service Center.

Ten cases of Mycobacterium avium subsp. hominissuis infections linked to equine abortions in Japan, 2018–2019
Yuta Kinoshita, Mari Takechi, Eri Uchida-Fujii, Kunio Miyazawa, Toshio Nukada, Hidekazu Niwa
Veterinary Medicine and Science, 18 December 2020 https://doi.org/10.1002/vms3.411

The study, published under a Creative Commons License, can be read here

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