Actinomycosis

OVERVIEW
An infectious disease caused by gram-positive, branching, pleomorphic, rod-shaped bacteria of the genus Actinomyces
A. viscosus—most commonly identified; survives in microaerophilic or anaerobic conditions
Rarely found as the single bacterial agent in a lesion; more commonly, it is a component of a polymicrobial infection.
There may be synergism between Actinomyces and other organisms.

SIGNALMENT
Dogs and cats
Especially common in young male dogs of sporting breeds

SIGNS
Infections—usually localized; may be disseminated; cervicofacial area commonly involved
Cutaneous swellings or abscesses with draining tracts—yellow granules (“sulfur granules”) may be seen in associated exudates.
Pain and fever
Exudative pleural or peritoneal effusions
Retroperitonitis—in one study, Actinomyces was identified in 3 of 34 affected dogs
Osteomyelitis of vertebrae or long bones—probably secondary to extension of cutaneous infection; lameness or a swollen extremity may develop
Motor and sensory deficits—reported with spinal cord compression by granulomas