Pseudotuberculosis (Corynebacteriosis)

Etiology:  Corynebacterium kutscheri is a Gram-positive short rod.

Incidence:  The incidence of infection is rare.

Transmission:  The bacteria are spread by direct contact.

Clinical Signs:  A subclinical infection is the most common form of infection.  Bacteria may be carried in the oral cavity and in cervical lymph nodes without disease in a chronically colonized animal.  Physiological stressors, immunosupression or other unknown factors may precipitate bacterial dissemination to the lungs, kidneys, liver, etc. with formation of abscesses and expression of overt clinical disease.  The rat may exhibit the typical sick rat syndrome (rough hair coat, hunched posture, anorexia) accompanied by dyspnea and an oculonasal discharge.

Pathology:  Large, often coalescing, white caseated purulent foci are present in the lungs (A.).  Histologically, there are purulent foci in the lung parenchyma (B.) with no involvement of the large airways.  Gram-stained lung sections or impression smears of lesions will reveal small gram-positive rods in active lesions (C.).  Active lesions eventually resolve.

Diagnosis:  Diagnosis is made by culture of lesions, oral washes and cervical lymph nodes.