Parasite Infection (Leishmaniasis) in Horses

There are multiple species of sandfly, which are primarily found in the Mediterranean. Sandflies of the genus Phlebotomus are associated with transmission of the Leishmania.

Previously, incidences of Leishmaniasis were not observed in North America outside of cases where infected individuals have been transported from endemic regions. The geographic range of sandflies is expanding with climate change, resulting in spreading occurrences of Leishmaniasis in previously unaffected regions, including North America.

This condition is considered an emerging disease in North America and has been identified in horses with no history of travel. It is not fatal to horses, however, it is zoonotic and capable of transmitting to humans and dogs for whom it can be fatal. If leishmaniasis is suspected, veterinary intervention is crucial for the horse and other mammals that have come in contact with it, including humans.

Horses with increased exposure to sandflies are at risk.

There are generally no other symptoms associated with leishmaniasis in horses. The number of lesions can vary depending on time of incubation and length of infection.

Leishmaniasis is caused by the infection of a protozoa from the Leishmania genus. The protozoa are transmitted by multiple species of sandfly from the Phlebotomus genus.

These lesions which can be found anywhere on the body but are most common in the head, pinnae, scrotum, legs, and neck. The lesions can be individual or a group, range in size from 0.5 - 10cm across, can be ulcerated or hair-covered, and are typically red in color.

After a physical examination and medical history, the primary method of diagnosis is microscopic visualization of a smear or biopsy of a lesion. Further analyses of the blood and/or tissue may be used for a definitive diagnosis.

Treatment can include a number of options;

• Surgical removal of lesions
• Treatment using pentavalent antimonial drugs
• Topical antifungal drugs

In horses, leishmaniasis is also capable of spontaneous regression and treatment is often needed in cases of chronic recurrence of the lesions.

Leishmaniasis has a good prognosis in horses. The lesions are the only symptom, the infection is localized to the skin, and the infection most often spontaneously resolves within 3-6 months.

The primary method of preventing leishmaniasis is by control of the sandfly population. Utilizing netting, habitat control, insecticides, avoiding peak exposure times, and covering areas of exposure on the body can reduce the chance of being infected by a sandfly bite.

Leishmaniasis is contagious and can be transmitted to other species, primarily humans and dogs, where it is fatal. Horses act as a vector for the transmission of the disease, and if present when bitten by a sandfly, that fly can then transmit it to a human or dog. Transmission can be minimized in humans and dogs similar to how it is reduced in horses.

Leishmaniasis is uncommon in horses.

• Surgical removal of lesions
• Pentavalent antimonial drugs
• Topical antifungal drugs