Veterinarian - University of Florida College of Veterinary Medicine

Research UpdateRare human parasite found in U.S. horse for thefirst time, UF researchers reportA rare, potentially fatal species of parasite never beforefound in North America has been identified in a Floridahorse.University of Florida veterinarians identified the parasite,called Leishmania siamensis, in the summer of 2011. Thisparticular species of parasite previously had been foundonly in Thailand and parts of Europe while other species ofLeishmania have been found all over the world. No Leishmaniainfections of any species had been previously reported in ahorse native to the United States.The UF discovery raises awareness of how widespread theparasite is and suggests a need for watchfulness regardingpotential transmission to humans, the researchers said.“We now know the parasites that cause this disease also existhere in the U.S. and that we have some insect, presumably thesandfly, that is capable of transmitting the disease,” said SarahReuss, V.M.D., a clinical assistant professor of large animalmedicine at the UF College of Veterinary Medicine, who alongwith UF colleagues and a private practice clinical pathologistdescribed the findings in the September issue of EmergingInfectious Diseases, a journal of the Centers for DiseaseControl and Prevention. “Our findings raise several potentialavenues of further investigation, including the prevalence ofthis disease in horses in the U.S., a better understanding of thesandfly life cycle and the potential of this leishmaniasis speciesto be transmitted from animals to humans.”Leishmaniasis is a parasitic infection spread through the bitesof infected sandflies. The disease shows up most commonlyin two forms: cutaneous, which causes sores on the skin, isself-healing; and visceral, the most severe form, which affectsthe entire body and is almost always fatal if left untreated.After malaria, leishmaniasis is the leading parasitic causeof death in humans. The disease has been found in fourcontinents and is considered to be endemic in 88 countries,including 16 developed nations, according to the World HealthOrganization. The WHO estimates the worldwide prevalenceat 12 million cases, with about 350 million people at risk ofinfection and about 60,000 people dying from the disease eachyear. Leishmaniasis is rare in people in the U.S.“It really hasn’t been a disease that has affected Americans, butthere are really good data with climate change models thatpredict sandfly ranges will expand, making this disease muchmore of a threat because of global warming,” said co-authorJames Wellehan Jr., D.V.M., Ph.D., a veterinarian from the UFresearch team, who confirmed the presence of the disease inthe Florida horse by analyzing the genes of the parasite.Photo by Maria FariasThe visceral form of leishmaniasis is endemicin foxhounds in the U.S, associated with adifferent species of Leishmania. But aside fromsome regional transmission in the Southwest,most of the cases of skin infection due toleishmaniasis in the U.S. are believed to haveoccurred in animals brought in from countrieswhere the disease is common, or in people whohad recently spent time in those countries.Dr. Sarah Reuss, right, shows the part of a horse’s ear where sores later confirmed to becaused by leishmania siamensis were seen and treated at UF in August 2011. The horse inthis photo was not affected by the disease. Dr. Jim Wellehan, left, looks on.“Thousands of people serving in the U.S.military have returned from Iraq andAfghanistan with cutaneous or visceralleishmaniasis,” said Christine Petersen, D.V.M.,Ph.D., an associate professor of veterinarypathology at Iowa State University’s Collegeof Veterinary Medicine and an expert onLeishmania transmission, immune responsesand veterinary disease, who was notinvolved in the study. “In a few cases, these14 | Florida Veterinarian