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Pet Owner Version

Actinomycosis in Horses


Geof W. Smith

, DVM, PhD, Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University

Last full review/revision May 2019 | Content last modified Sep 2022

Actinomyces bacteria normally live in the mouth and in the nasal passages near the throat. One species, Actinomyces bovis, has been identified infrequently in infections in horses, including chronic fistulous withers and chronic poll evil Fistulous Withers and Poll Evil Depending on the condition, joint disorders can affect the joint membranes, surrounding tendons, underlying bone, cartilage, bursae, and/or fluid within the joint (synovial fluid). Arthritis... read more . Disease occurs when this bacterium invades soft tissues by way of penetrating wounds of the mouth (such as those that occur from chewing wire or coarse hay). Involvement of the nearby bone frequently results in facial distortion, loose teeth (making chewing difficult), and difficulty breathing due to swelling of the nasal cavity. Treatment is rarely successful in longterm cases in which bone is involved, due to the poor penetration of antibacterial drugs into the affected area. In less advanced cases, your veterinarian may prescribe an antibiotic.

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