Causative Agent: Malignant catarrhal fever (MCF) is caused by a herpes virus. There are two types of herpes viruses that cause MCF. Alcelaphine herpesvirus 1 is carried by the African wildebeest. Ovine herpesvirus 2 is carried by sheep and goats throughout the world. The virus does not cause disease in sheep and goats, but can be spread to cattle and cause disease.
Clinical Signs: When the herpes virus is spread to cattle, the incubation period (period of time from exposure to the virus to the time clinical signs first appear) is 3-10 weeks. Cattle have an acute (rapid) onset of clinical signs. These signs may include fever, lethargy, enlarged lymph nodes, excessive tearing, mucous discharge from the nose, ulcers in the mouth, inflammation of the eyes and lining of the eyelids, and diarrhea. Other signs include encrustation (scabbing) of the muzzle, salivation due to severe oral ulceration, a cloudy appearance of the eyes with pus present within the eyeball(s). Ulceration may occur around the anus and vulva, at the junction between the skin and hoof wall (coronary band), on the skin between the claws, and on the teats. Some animals exhibit central nervous system signs such as excitability, increased sensitivity to stimuli, muscle tremors, and occasionally convulsions. Aggressiveness, similar to that seen with rabies, is another central nervous system sign. The course of disease may last 3-7 days.
Disease Transmission: In wildebeest calves, MCF may be spread in nasal and eye secretions and in manure. When cattle come in contact with infected sheep, they can become infected with the virus. Contaminated calving equipment is also thought to spread the virus to other cattle.
Diagnosis: The diagnosis of MCF is made based on a history of exposure, clinical signs, and microscopic analysis of tissues (after the animal has died). Microscopic analysis reveals a severe inflammation of the lining of blood vessels and deterioration of skin (epithelial) surfaces. There are several specialized laboratory tests that may suggest a diagnosis of MCF. These tests include: virus neutralization, indirect immunofluorescense, immunoperoxidase, conventional ELISA, competitive inhibition ELISA, and polymerase chain reaction (PCR). Diseases that have clinical signs similar to malignant catarrhal fever include rinderpest, bluetongue, vesicular diseases, East Coast cattle fever, infectious bovine rhinotracheitis, bovine viral diarrhea and mucosal disease, shipping fever, rabies, and tick-borne encephalitides.
Treatment/Prevention: Survival from MCF is rare. Treatment is primarily supportive with intravenous (IV) fluids. Antibiotics may be administered to control secondary bacterial infections. To prevent the spread of malignant catarrhal fever, cattle should not come in contact with African wildlife, especially wildebeests. It is also important to avoid grazing sheep and cattle together or in neighboring fields.