Malignant catarrhal fever (MCF)
Malignant catarrhal fever is invariably fatal generalized lymphoproliferative disease of cattle and sometimes of wild ruminants. It is common in Africa, parts of Europe and in feedlot cattle in North America. The disease primarily affects lymphoid tissues and epithelial cells of respiratory and gastrointestinal tract. Sheep act as reservoir for MCF virus.
Epidemiology: The disease primarily affects adult cattle. Sheep act as carriers of the virus. The aetiological agent, a member of the sub-family Gammaherpesvirinae, is designated as Alcelaphine herpes virus-1. Cattle are believed to be infected via the relatively large amounts of virus present in the nasal secretions of wild beast calves. The virus is not transmitted between cattle, which appear to be dead end hosts.
Symptoms: The disease is characterized by high fever with copious discharge from the mouth, nose and eyes. Ulcers covered with necrotic tissue deposits are seen on the tongue, gums, inside of the cheek and certain other parts. Vesicles appear all over the body, and the face and head are swollen. Usually the animals die in about a week.
Diagnosis: The disease is diagnosed by the absence of diarrhoea and the presence of copious discharges from the nose and eyes, and by absence of ulcers in the abomasum and intestines of dead animals, though it can create confusion with rinderpest. The virus can be isolated when washed peripheral blood leukocytes are inoculated in calf thyroid cells. Cell free inocula do not yield virus. The cytopathic changes require at least 3 days to appear and several passages in cell culture are often necessary. They are characterized by syncytia formation and by the presence of typical herpesvirus intranuclear inclusion bodies.
Treatment, prevention and control: Symptomatic treatment helps in the natural process of recovery. At present, no effective vaccine is available for the prevention of the disease. Cattle serve as dead end hosts and susceptible animals pick up the infection from wild bovidae especially from nasal secretions of infected wild beast calves. Attempt to develop a vaccine have been unsuccessful so far.