Leishmaniasis: A Rare, Potentially Emerging Equine Disease

Leishmaniasis: A Rare, Potentially Emerging Equine Disease

If you are taking steps to minimize insect bites to prevent West Nile virus and Eastern equine encephalitis, you're also already taking steps protect yourself and your horse from leishmaniasis.

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If you are taking steps to minimize insect bites to prevent West Nile virus and Eastern equine encephalitis, you're also already taking steps protect yourself and your horse from a parasitic disease called leishmaniasis. And according to a group of Florida-based veterinarians, this currently uncommon disease has the potential to be seen more frequently in North America.

Leishmania spp. are microscopic parasites (not viruses) spread by female sand flies. After an infected fly bites and transmits the parasite to the horse, the parasite can cause problems on the animal's skin or spread throughout the body.

"In horses, cutaneous (skin) leishmaniasis usually presents with solitary or multiple nodules that are often ulcerated," explained Sarah Reuss, VMD, Dipl. ACVIM, clinical assistant professor at the University of Florida's College of Veterinary Medicine. "The ulcers are most frequently noted on the head, ears, legs, and neck. (Currently) leishmaniasis is only infrequently described in any species in Florida, and it usually only occurs in people or animals that have traveled to areas of the world such as the tropics and subtropics."

There are, however, geographical "pockets" throughout North America where leishmaniasis is well-described in fox hounds and humans without a history of travel.

In a recent letter to the journal Emerging Infectious Diseases, published by the Centers for Disease Control and Prevention, Reuss and colleagues described a 10-year-old Morgan horse mare residing in Florida who presented with a small, one centimeter diameter, hair-covered mass in the left ear (termed a pinna). After the mare was bred and confirmed in foal, the mass in the ear began to grow and ulcerate, and new masses were noted on her neck, shoulders, and withers.

"A biopsy and DNA testing identified protozoal organisms consistent with Leishmania siamensis," Reuss said. "This particular species of Leishmania had never been identified in North America before, but is a known cause of disease in humans in Asia.

"The mare unfortunately delivered a stillborn foal at 350 days, but within one month of foaling, the mare's lesions were 90% resolved," she noted. Reuss noted that the mare's masses were treated with local injections of amphotericin B and systemic fluconzaole, both antifungal medications.

Because the mare had been born in and had not left the United States, this appears to be the first published indigenous case of leishmaniasis in a horse in this country.

Reuss noted, "Sand flies capable of spreading leishmaniasis are indigenous (already exist) in Florida, and climate changes are contributing to the increased range of those flies. Considering that leishmaniasis appears to already exist in the U.S., efforts need to be made to better understand the prevalence of leishmaniasis in horses in the U.S., how the parasite is spread, which sand flies exactly can spread the parasite, and what other species can be infected."

The letter, "Autochtonous Leishmania siamensis in Horse, Florida, USA" by Reuss et al. is available online.

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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