A deadly discovery

A deadly discovery

UF veterinary researchers identify rare parasite in Florida horse

By Sarah Carey

UF veterinarian Sarah Reuss, V.M.D., and colleagues, including Jim Wellehan, D.V.M., Ph.D., have identified a rare, potentially fatal species of parasite in a Florida horse./Photo by Maria Belen Farias

A rare, potentially fatal species of parasite never before found in North America has been identified in a Florida horse.

UF veterinarians identified the parasite, called Leishmania siamensis, in 2011 and described the findings in the September issue of Emerging Infectious Diseases, a journal of the Centers for Disease Control and Prevention. This particular species of parasite previously had been found only in Thailand and parts of Europe. No Leishmania infections of any species had been previously reported in a horse native to the United States.

The discovery raises awareness of how widespread the parasite is and suggests a need for watchfulness regarding potential transmission to humans, the researchers said.

“We now know the parasites that cause this disease also exist here in the U.S. and that we have some insect, presumably the sandfly, that is capable of transmitting the disease,” said Sarah Reuss, V.M.D., a clinical assistant professor of large animal medicine at the College of Veterinary Medicine. “Our findings raise several potential avenues of further investigation, including the prevalence of this disease in horses in the U.S., a better understanding of the sandfly life cycle and the potential of this leishmaniasis species to be transmitted from animals to humans.”

Leishmaniasis is a parasitic infection spread through the bites of infected sandflies. The disease shows up most commonly in two forms: cutaneous, which causes sores on the skin and is self-healing; and visceral, the most severe form, which affects the entire body and is almost always fatal if left untreated.

After malaria, leishmaniasis is the leading parasitic cause of death in humans. The disease has been found in four continents and is considered to be endemic in 88 countries, including 16 developed nations, according to the World Health Organization. The WHO estimates the worldwide prevalence at 12 million cases, with about 350 million people at risk of infection and about 60,000 people dying from the disease each year. Leishmaniasis is rare in people in the U.S.

“It really hasn’t been a disease that has affected Americans, but there are really good data with climate change models that predict sandfly ranges will expand, making this disease much more of a threat because of  global warming,” said co-author James Wellehan Jr., D.V.M., Ph.D., a veterinarian from the UF research team, who confirmed the presence of the disease in the Florida horse by analyzing the genes of the parasite.

Aside from some regional transmission in the Southwest, most of the leishmaniasis skin infection cases in the U.S. are believed to have occurred in animals brought in from countries where the disease is common, or in people who had recently spent time in those countries.

But the horse diagnosed at UF had no history of travel outside of the eastern U.S. The pregnant 10-year-old Morgan mare was treated as an outpatient at the UF Large Animal Hospital for sores inside her left ear.

“Many of the horses in other countries that have been diagnosed with leishmaniasis were pregnant, so we think perhaps these horses have pregnancy-altered immune systems and are therefore more vulnerable to the disease,” Reuss said.