Actinomycosis

What it is

Bovine actinomycosis is a chronic bone infection caused by Actinomyces bovis, a Gram-positive, filamentous, anaerobic bacterium that normally lives in the oral cavity. It enters the tissues through wounds in the mucosa caused by coarse forage, grass awns or foreign bodies, or through the alveoli during tooth eruption. In bone it causes rarefying osteomyelitis: it destroys bone and at the same time stimulates periosteal new bone formation, so the bone becomes thickened with a honeycomb appearance. The lesions are pyogranulomas containing small yellowish granules of bacterial colonies (so-called "sulphur granules").

It must be distinguished from actinobacillosis (wooden tongue), caused by Actinobacillus lignieresii, which mainly affects soft tissues such as the tongue and lymph nodes and responds better to treatment.

Who it affects

Cattle of any age, sporadically, especially young animals at the time of permanent tooth eruption and animals eating coarse or fibrous forage. It is not usually transmitted between animals.

Anatomy involved

• Mandible: the most common site. The lesion affects the body of the mandible at the level of the cheek teeth (premolars and molars), where the bacterium enters through the alveoli or through gum wounds. The bone swells, the teeth loosen or become misaligned and chewing becomes difficult.
• Skull (maxilla): the maxilla and other facial bones are affected less often. The lesion can extend into the nasal cavity or pharynx and cause breathing difficulty.
• Unlike actinobacillosis, the regional lymph nodes are not usually involved.

Clinical signs

A hard, immovable swelling of the mandible or maxilla, at first not very painful, which grows slowly over weeks or months. In time it becomes painful and sinus tracts open in the skin, draining thick pus with yellowish granules. The affected teeth loosen, the animal chews with difficulty, drops feed and loses weight. When the maxilla is involved there may be nasal discharge and dyspnoea.

Diagnosis

• Clinical: the location and appearance of the swelling are very characteristic.
• Radiography: bone destruction with multiloculated radiolucent areas and periosteal new bone formation; it also shows involvement of the alveoli and teeth. Computed tomography is used in referral centres.
• Cytology and culture: pus crushed between two slides shows the granules with branching Gram-positive filaments; anaerobic culture confirms the agent.
• Histopathology: pyogranulomas with bacterial colonies surrounded by club-shaped eosinophilic material.
• Differential diagnosis: actinobacillosis, tooth root abscesses, fractures with osteomyelitis and neoplasia.

Treatment

The aim is to halt progression of the lesion: bone that is already deformed does not regain its shape. In early lesions, intravenous sodium iodide, sometimes repeated, is used together with antimicrobials such as penicillin, and surgical debridement and drainage of the sinus tracts. Signs of iodism (lacrimation, skin scaling, coughing, loss of appetite) must be monitored. In advanced lesions the response is poor and, when the animal cannot eat properly, slaughter is usually recommended. Drug use in food animals is subject to national regulations and withdrawal periods, and not all these products are authorised in every country.

Key studies

The evidence is very limited. No systematic reviews, controlled trials or cohort studies on bovine actinomycosis were found in PubMed; textbook recommendations for diagnosis and treatment rest on clinical experience and small case series. The best available sources are cited, with that caveat:

• Silva et al. (2004), uncontrolled series of 12 cattle and 2 horses treated locally with metacresolsulfonic acid and streptomycin. 87% of the animals were considered clinically cured, with no relapse at 6 months. It is a small series, without a control group and with mixed species.
• Christener et al. (2026), series of 5 cattle referred to a ruminant clinic. The disease was often detected late, when it was already too advanced to treat: slaughter was recommended in 2 cases, and 2 cases detected early could be treated. Radiological imaging was the method of choice for diagnosis in the live animal, and in one case it was confirmed with computed tomography. It is a very small descriptive series.