Actinobacillosis

This is a sporadic infection of the lips and cheeks (sheep) and tongue (cattle) caused by Actinobacillus lignieresii, a bacterium normally resident in the mouth.

Mucosal abrasion or injuries to the tongue allow bacteria to establish infection. Cases may be more likely to occur in dry periods or when feeding coarse or prickly feed. The tongue becomes progressively disabled by swelling and fibrosis, and affected animals suffer weight loss due to difficulty eating and drinking.

The infection is chronic and progressive. Early lesions may not be detected in pre-export inspections and may therefore present during export.

Infection causes swelling associated with granulomatous abscesses in the tongue (cattle) or other oral tissues. Affected animals will have difficulty eating and generally lose weight.

Cattle will show drooling, tongue-lolling, chewing movements, protrusion of the tongue and bottle jaw. Finding a thick, hard, dry tongue is diagnostic.

Sheep will often show numerous small abscesses containing yellow granular pus in the soft tissues under the skin of the face. The abscesses often burst through the skin and thick pus can be expressed by squeezing. Spread to the nasal cavity may cause respiratory distress.

Differential diagnoses include oral foreign bodies such as a bone or stick, broken teeth or jaw, or a grass seed abscess affecting lymph nodes of the throat. At necropsy, affected areas contain numerous pus-filled yellow granules.

Laboratory confirmation requires a smear of pus from deep within the lesion for microbiology. Sections of skin and subcutaneous tissue may also be submitted in buffered formalin for histology.

Treatment with sodium iodide or a course of antibiotics (procaine penicillin, oxytetracycline, or erythromycin) is usually curative. In advanced cases there may be irreversible fibrosis of affected tissues and cattle may not regain normal tongue function.

The unpredictable and infrequent occurrence on farm or feedlot does not warrant special control measures. Awareness of the condition and systems for early detection are therefore important.