Climate and leishmaniasis: Horses May Be a Major Reservoir for the Parasite

Leishmaniasis is a zoonosis considered endemic in the Mediterranean region. The infection is transmitted through the bites of sandflies infected with Leishmania infantum. Although dogs have long been considered the main reservoir for the parasite, other animals can also serve as reservoirs, such as cats, carnivores, wild birds, reptiles, and now horses. The importance of horses in parasitic transmission is particularly linked to the close relationship between this species and humans.   A Spanish study assessed the prevalence and factors associated with L. infantum infection in apparently healthy horses in eastern Spain, an area where the parasite is endemic. In general, infected horses exhibit only mild clinical signs that often go unnoticed, and reported cases of equine leishmaniasis are rare in Europe. Thus, horses may be resistant to Leishmania infection due to an effective immune response of their immune system. To detect the possible presence of L. infantum , the scientists collected epidemiological data from the study area and serum samples were collected from 167 healthy horses living in the Valencia region between December 2022 and June 2023. These horses showed no clinical signs of infection, such as skin lesions, yet 27.5% of them tested positive and had anti-Leishmania antibodies, indicating exposure to the disease. In addition, several factors influencing infection were identified:

• breed and morphology: 75% of the positive equines were ponies, 57% were Spanish sport horses, and 33% were purebred Spanish horses;
• housing: horses kept outdoors had a significantly higher prevalence (39% versus 5.5%);
• activity: 89% of horses used for riding instruction tested positive;
• season of sampling: 60.7% of samples tested positive in the spring, and only 8.5% in the winter.

  While the authors remain cautious regarding the breed factor, they confirm certain previous observations: the meso-dolichomorphic type (light horses used in sports and recreation) is more prone to infection by the leishmaniasis vector, but it is primarily the lifestyle that promotes infection by the parasite (outdoor access, trail rides, outdoor sports, etc.). The study also shows that prevalence is higher during the warmer seasons, suggesting that the risk of spread is correlated with rising temperatures, which favor the development of sandflies and other parasites. This significant prevalence, in a region where human leishmaniasis has been endemic since 1982, indicates that horses could serve as a silent reservoir for the disease’s vector. According to the authors, it would therefore be worthwhile to implement control measures for this zoonosis in horses—through the use of repellents, for example—as part of a “One Health” approach. This is because, in the future, rising temperatures due to climate change will likely increase the prevalence of Leishmania infections in all species, including humans. Horses also serve as natural sentinels for other diseases, notably West Nile fever, which is currently rampant in France and is spreading further and further north.     https://vetitude.fr/leishmaniose-canine-EFSA-la-caracterisation-de-la-maladie-et-prevention/