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Pet Owner Version

Actinomycosis in Dogs


Geoffrey W. Smith


Reviewed/Revised Jun 2018 | Modified Oct 2022

Actinomyces bacteria normally live in the mouth and in the nasal passages near the throat. Several species are associated with diseases in dogs.

Actinomyces bovis has been identified infrequently in infections in dogs and other mammals. Disease occurs when this bacterium is introduced to underlying soft tissue through penetrating wounds of the mouth (such as those that occur from carrying sharp objects in the mouth or running through underbrush). 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 extensively involved, due to poor penetration of antibacterial drugs into the infected area. In less advanced cases, your veterinarian may prescribe an antibiotic.

Actinomyces hordeovulneris causes abscesses (collections of infection and pus) and generalized infections, such as inflammation of the cavity surrounding the lungs, inflammation of the lining of the abdomen, abscess on internal organs (such as the liver and spleen), and bacterial arthritis in dogs. An infection that causes pus to accumulate around the lungs (called pyothorax) is frequently seen. One factor that appears to be related to infection with this organism is the presence of foxtail grass (Hordeum species) particles that have migrated into the body tissues, allowing penetration of the bacteria. Treatment includes surgical removal of the contaminated tissue and drainage, followed by longterm treatment with an antibiotic. Animals with pyothorax must have the pus drained from their chests, in addition to treatment.

Actinomyces viscosus causes abscesses to form under the skin in dogs. Lesions generally develop after a traumatic injury, such as a bite wound. The most commonly affected locations include the head, neck, thorax, and abdomen. The bacteria can also cause chronic pneumonia, inflammation of the cavity surrounding the lungs, and nervous system infections. Treatment of inflammation of the chest cavity with an antibiotic may be successful if begun early in the disease course. Treatment is more likely to be successful with a localized infection under the skin, which your veterinarian will also treat with an antibiotic.

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