Researchers with Addis Ababa University in Ethiopia have found a strong correlation between the rate of histoplasmosis (epizootic lymphangitis) and the climate of the area in which horses live. The study was published in the July Veterinary Journal.
According to the Merck Veterinary Manual: “Epizootic lymphangitis is a chronic granulomatous disease of the skin, lymph vessels, and lymph nodes of the limbs and neck of Equidae caused by the dimorphic fungus Histoplasma farciminosum. The disease is seen in Asian and Mediterranean areas, but is unknown in the USA.”
Clinical signs include cutaneous nodules that go through periods of discharge of creamy exudates and closure. The skin surrounding the nodules can thicken and fuse to underlying tissues. Merck says that lesions can also be present in the lungs, conjunctiva, cornea, nasal mucosa, and other organs.
According to this study, up to 39% of horses in specific towns in Ethiopia are affected.
No correlation was found to annual rainfall, but cases increased in hot, humid towns with altitudes between 1500 meters and 2300 meters above sea level. Cold, dry areas had significantly fewer cases. It was concluded that annual temperature has a strong correlation to histoplasmosis infection rates.