This neglected disease has a significant welfare impact on working equids and has economic importance to many resource-poor owners with inadequate access to animal health services who rely on animals for their livelihoods. | Photo: Stephanie L. Church/The Horse

Epizootic lymphangitis is a systemic infection of equids, caused by the dimorphic soil fungus Histoplasma capsulatum var. farciminosum. Donkeys are less commonly affected than horses and mules. It has been reported in both camels and cattle, and anecdotally in humans.

The disease has been eradicated from many countries, but remains a problem for equids, particularly in northern Africa, Asia, and the Middle East. It is contagious, spreading between animals through inhalation, skin contact with infected discharges, fomites, and insect vectors. Skin wounds are common entry sites for the organism.

Three forms of the disease exist: cutaneous, ocular, and respiratory. The cutaneous form is most common, causing a chronic, suppurative, ulcerating pyogranulomatous dermatitis and lymphangitis. Initial nodules appear anywhere on the body but commonly on lower limbs, chest, and neck. Nodules rupture, discharging thick pus, and the ulcerated lesions subsequently scar and heal. Lesions progress locally along lymphatics, which become beaded and rope-like with enlarged regional lymph nodes. Repeated cycles of ulcerating and healing nodules occur