Malignant Catarrhal Fever

The causative virus is carried by, but does not cause disease in, sheep and can be spread to cattle by these silent carriers of disease. In the UK, the virus that causes malignant catarrhal fever is ovine herpesvirus 2 (OHV-2). The means of transmission of OHV-2 is not known, although it is known to be spread by neonatal lambs in particular (although all ages can be infectious). It is thought that

fairly close contact between susceptible animals and sheep is necessary for spread of disease. It appears that the virus does not spread easily between individual cattle, and while cases of cattle to cattle transmission have been documented, this seems to be rare. The virus may take anywhere from 9 to 200 days from infection to development of clinical signs in the host animal. Some animals do not develop disease unless subjected to periods of stress that allow the virus to invade. Clinical Signs

Typical infections present as

Sudden death
Fever with clear, watery discharge from eyes and nose, which may become thicker and yellow in colour (mucopurulent)
Mucous membranes and skin may become ulcerated and/or necrotic
Corneal opacity starting at the rim of the cornea and moving inwards
Other signs that may be observed include

Depression
Disseminated intravascular coagulation, seen as areas of bruising or bleeding into the skin and mucous membranes (gums, v***a etc.) Dyspnoea (difficulty breathing)
Inappetance
Increased salivation
Horn and hoof covering may become loosened and fall away from the underlying skin
Swollen joints
Reduced milk yield
Neurological signs such as lowered pain threshold, head pressing, incoordination, etc. Post Mortem Signs

Epithelial surfaces are haemorrhagic and/or ulcerative
Lymphoid tissues and the liver may be enlarged
Histology shows damage to epithelium and blood vessels
Treatment

Treatment is often unsuccessful and the prognosis is poor. The disease is fatal in almost all animals that show clinical signs.