VMC 311: Systematic Veterinary Bacteriology and Mycology (2+1)

PATHOGENICITY

Symptoms

• Clinical signs develop after prolonged subclinical phase of infection. Affected cattle are usually more than 2 years of age when signs are first observed.
• In cattle, the disease is characterized by diarrhoea, initially intermittent, dark and semisolid, but becoming persistent and profuse.
• Progressive weight loss results without loss of appetite, leading to emaciation and eventually death.
• The mortality rate may approach 100%. Asymptomatic carrier cattle have an increased incidence of mastitis and infertility.
• In sheep and goats, the disease is clinically evident only in mature animals. The diarrhoea is less marked and may be absent.

Lesions

• Chronic catarrhal inflammation of the intestine is characteristic.
• In cattle, the mucosa of affected areas of the terminal small intestine and the large intestine is usually thickened and folded into transverse corrugations.
• The mesenteric and ileocaecal lymphnodes are enlarged and oedematous.
• Thickening of the intestinal mucosa is less marked in sheep, and necrosis and caseation may be present in the regional lymphnodes.