Actinomyces spp are normal flora of the oral and nasopharyngeal mucous membranes. Members of the genus Actinomyces are gram-positive, non-acid-fast rods, many of which are filamentous or branching. Branches are <1 µm in diameter, as opposed to fungal filaments, which are >1 µm in diameter. Several species are associated with diseases in animals.
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Actinomyces bovis, Gram-stained smear
Actinomyces bovis, Gram-stained smear
A bovis is the etiologic agent of lumpy jaw in cattle. It has also been isolated from nodular abscesses in the lungs of cattle and from infrequent infections in sheep, pigs, dogs, and other mammals, including chronic fistulous withers and chronic poll evil in horses. Lumpy jaw is a chronic, progressive, indurated, granulomatous, suppurative abscess that most frequently involves the mandible, the maxillae, or other bony tissues in the head.
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Lumpy jaw, cow
Lumpy jaw, cow
Disease is seen when A bovis is introduced to underlying soft tissue, via penetrating wounds of the oral mucosa from wire or coarse hay or sticks. Involvement of adjacent bone frequently results in facial distortion, loose teeth (making chewing difficult), and dyspnea from swelling into the nasal cavity. Diagnosis can be based on clinical signs alone, but demonstration of gram-positive rods in yellowish “sulfur granules” from aspirated purulent material, as well as bacteriologic culture and histopathology, are confirmatory. The organism appears as long filaments, rods, and cocci in exudate from active lesions. Treatment is rarely successful in chronic cases in which bone is extensively involved, due to poor penetration of antibacterial agents into the site of infection. In less advanced cases, penicillin may be effective. Systemic treatment with potassium iodide has been used successfully in the past, but is no longer recommended due to food safety issues.
A hordeovulneris causes localized abscesses and systemic infections, such as pleuritis, peritonitis, visceral abscesses, and septic arthritis in dogs. A common predisposing factor is the presence of tissue-migrating foxtail grass ( Hordeum spp ) particles. History and clinical signs may contribute to the diagnosis, but demonstration of the causative agent by Gram’s stain and bacteriologic culture is necessary for confirmation of etiology. Treatment includes surgical debridement and drainage and longterm treatment with penicillin or clindamycin.
A israelii is primarily associated with chronic granulomatous infections in humans, but has also been isolated rarely from pyogranulomatous lesions in pigs and cattle. Treatment involves surgical debridement and administration of penicillin. Clindamycin is also effective in porcine infections.
A naeslundii has been isolated from suppurative infections in several animal species, the most common being aborted porcine fetuses.
A (Corynebacterium) pyogenes has now been reclassified as Arcanobacterium pyogenes . It is associated with infections in many organ systems in multiple species of domestic animals; it is perhaps most common in cattle, but is found in goats, sheep, pigs, and others. Conditions include acute and chronic suppurative mastitis, suppurative pneumonia (usually as a sequela of acute bovine respiratory disease caused by Mannheimia haemolytica or Pasteurella multocida ), septicemia, vegetative endocarditis, endometritis, septic arthritis, wound infections including umbilical infections, seminal vesiculitis (bulls and boars), and summer mastitis. Liver abscesses in feedlot cattle often involve A pyogenes , alone or in combination with Fusobacterium necrophorum . Diagnosis is accomplished easily by bacteriologic culture and identification of the organism. Surgical debridement and drainage may be useful in treatment, and antimicrobials such as penicillin may be useful as well. Tylosin is commonly used as a preventive in feedlot rations.
A suis causes pyogranulomatous porcine mastitis, characterized by small abscesses containing viscid, yellow pus surrounded by a wide zone of dense connective tissue. Yellow “sulfur granules” may be scattered throughout the pus, as in A bovis in cattle. Chronic, deep-seated abscesses may fistulate. Sows may also develop ventral subcutaneous granulomatous lesions, and occasional pyogranulomatous infections develop in lungs, spleen, kidneys, and other organs. Diagnosis is based on clinical signs and on isolation and identification of the etiologic agent. Treatment is rarely successful, primarily due to the inability of an antibacterial agent to penetrate the infected tissue. Infected tissue is often surgically removed to salvage sows for slaughter.
A viscosus causes chronic pneumonia, pyothorax, and localized subcutaneous abscesses in dogs. Thoracic lesions are pyogranulomas, whereas cutaneous lesions are granulomatous abscesses, often with fistulous tracts. Lesions generally develop after a traumatic injury such as a bite wound. Diagnosis may be based on history and clinical signs, including the presence of soft, grayish white granules in the pus or exudate, and isolation and identification of A viscosus . Treatment of pyothorax with penicillin or clindamycin may be successful if begun early in the clinical course. A successful outcome is more likely with cutaneous infections, which should also be treated with the same antimicrobials.