Leptospirosis is a neglected zoonotic disease caused by pathogenic Leptospira bacteria and can affect humans and animals, including horses.

A new study published in BMC Veterinary Research analyzed how exposure to Leptospira is common in horses in Connecticut and what strains they had been exposed to.

This work was led by Dr. Camila Hamond, assistant research professor in the Department of Pathobiology and Veterinary Science in the College of Agriculture, Health and Natural Resources (CAHNR).

Equine leptospirosis can result in abortion, stillbirth, neonatal death, placentitis, and uveitis Equine recurrent uveitis (ERU) or “moon blindness.” ERU is a common cause of ocular pain and blindness in horses, and it can lead to decreased sports performance. Foals are also particularly susceptible to acute illness.

“Horses play an important role in the lives of Connecticut residents in the form of leisure pursuits and related business activities,” Hamond says. “If horses have reproductive problems, this can impact production and potentially the [economy] too.”

The UConn team tested nearly 400 samples for 40 different strains of Leptospira. Dr. Elsio Wunder’s group received the samples from the Connecticut Veterinary Medical Diagnostic Laboratory (CVMDL), a nationally accredited veterinary diagnostic laboratory located at UConn Storrs. The CVMDL shared samples that had been submitted by horse owners to test for other diseases.

The results showed that 61.5% of samples had antigens associated with one strain of Leptospira. The most detected serogroups were Djasiman, Grippotyphosa, Australis, Pomona, and Icterohaemorrhagiae.

“The test we used can identify animals exposed to Leptospira, but does not differentiate between an antibody response from natural infection or vaccine response,” Hamond says. “These results do not mean [that percentage of horses were] infected, it means [they were] exposed.”

There is a vaccine available to protect horses against Leptospira. However, it only targets the serogroup Pomona. In this study, Pomona only accounted for 10% of positive results. It is not clear if the antigens were a result of vaccination or natural infection.

Horses can come into contact with pathogenic Leptospira through direct contact with infected animals or contaminated environments. The pathogen has the ability to survive in suitable moist environmental conditions facilitating spillover infections and disease transmission to humans and other susceptible animals. In the United States, most human cases of leptospirosis are associated with occupational exposure to infected animals, recreational exposures, and individuals living in economically disadvantaged inner-city environments.

Asymptomatic horses can shed different species and serogroups of Leptospira via urine.

“This is a problem, because they can shed it and contaminate the environment, contaminate humans, and we can get acute disease,” Hamond says. “This is why the concept of One Health, which explores the interconnectedness of human, environmental, and animal disease, is so important.”

CAHNR continues to lead UConn’s efforts to expand One Health education, research, and collaboration.

While extremely rare, horses can transmit Leptospira to humans. Those who work with horses infected should wear personal protective equipment and implement biosecurity practices to prevent direct contact with urine and fetal tissues from infected horses. Infected horses should be isolated for three to four weeks. Their urine should test negative for Leptospira before release, according to guidance from the American Association of Equine Practitioners (AAEP).

Vaccination and farm management practices that prevent contact with wildlife and replace or prevent access to stagnant water, especially after periods of high rainfall and flooding, can help prevent infection.

The results in this paper mirror results found in other states with large horse populations. But the problem may be even wider, as leptospirosis in horses is under-researched compared to animals, like canine, bovine, and swine.

“There is leptospirosis in Connecticut too. But only a few states are studying leptospirosis in horses such as Kentucky, North Carolina, and Colorado,” Hamond says.

Wunder and Hamond are now working on expanding their study to include other New England states. They have also developed a new qPCR test to detect all pathogenic Leptospira species.  Direct detection of leptospires by culture or qPCR is required to identify asymptomatic reservoir hosts of infection.

“This is just the beginning,” Hamond says. “It’s just the serology to see if the animal is exposed. Now we have a new approach to detect all the pathogenic species in clinical samples from animals.”

Horse owners can find more resources about leptospirosis in horses in the Merck Veterinary Manual.

 

This work relates to CAHNR’s Strategic Vision area focused on Enhancing Health and Well-Being Locally, Nationally, and Globally.

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