Malignant Catarrhal Fever or Bovine Malignant Catarrh

Filed Under: Cows, Diseases

Malignant Catarrhal Fever (MCF) or Bovine Malignant Catarrh are actually two diseases caused by separate herpes viruses that are almost always fatal to cattle, deer, bison, occasionally pigs, rabbits, and certain exotic ruminants. Neither virus causes disease in their principal hosts, either the wildebeest or the sheep.

Two strains of MCF occur. One strain originates from sheep and possibly goats and is known as the Ovine herpesvirus-2 (OHV-2). Although the ovine strain is considered to be endemic in the United States, outbreaks are uncommon. The Alcelaphine Herpesvirus-1 (AHV-1) is associated with wildebeest and close relatives thereof. AHV-l is endemic in Africa where cattle freely intermingle with wildebeest. An as yet unidentified strain is believed to cause MCF in white-tailed deer.

MCF is characterized by erosive stomatitis (mouth infection), erosions in the upper respiratory tract, a severe nasal and ocular discharge with keratoconjunctivitis (inflammation of the cornea and conjunctiva or tissue surrounding the eye) and complicating corneal opacities. Additional clinical signs include encephalitis, cutaneious exanthema (erythema or redness, exudation, cracking, and crust formation on coat), and lymph node enlargement. A high fever of up to 107º F and diarrhea may occur, often being blood-stained. Mild or inapparent infections are characterized by chronic alopecia (hair loss) and weight loss. Hoofs and horns may be shed with lameness being pronounced. Hematuria or blood in the urine is often seen.

Typically close contact is required with sheep, goats or wildebeest for transmission, although there have been reports of it spreading several hundred feet. The virus is fragile and sensitive to environmental desiccation and inactivation. Disease in pigs has been associated with petting zoos where sheep and pigs intermingle. Transmission between cattle does not occur. The spread of the virus is though to be highest when sheep or wildebeest give birth to their offspring. Typically sheep are infected at 1 to 2 months of age and begin shedding the virus at 6 months of age, with shedding leveling off at around 10 months of age. Affected wildebeest actively shed the virus until 3 to 4 months of age.

The incubation period of MCF typically takes from 7 to 14 days, but latent infections may occur up to 200 days following infection. The course of the disease runs from 1 to 10 days and is fatal in 90% to 100% of affected animals.

Most outbreaks of the AHV-1 strain in the United States have occurred in zoos. An outbreak occurred in March of 2008 and was associated with exotic animals at a large Texas ranch.

Disease may be detected serologically by competitive inhibition enzyme-linked immunosorbent assay or ELISA testing. Viral DNA may also be detected by a polymerase chain reaction, or PCR.

Treatment is supportive in endemic areas. Non-steroidal and anti-inflammatory drugs may help to relieve some of the discomfort in diseased animals. Euthanasia of affected animals is suggested in non-endemic areas.

The differential diagnosis of MCF should include BVD, IBR, bluetongue, rinderpest, vesicular stomatitis, foot and mouth disease, sporadic bovine encephalomyelitis, Jembrana disease, and acute shipping fever.

To prevent exposure, avoid mixing herds of sheep, cattle, and exotic ruminants. At the present time no vaccine is available.

References:

Animal Health Newsletter. Alabama Department of Agriculture and Industries. USDA, APHIS, Veterinary Services. Vol. 2, Issue 2. March – June 2008. P. 1.

Kahn, Cynthia, Ed. The Merck Veterinary Manual. 9th Edition. Merck and Co. Inc. 2005. Pp. 609-611.

Radostits, Otto and Clive Gay, et al. Veterinary Medicine. 10th Edition. Saunders/Elsevier. 2007. Pp. 1245-1248.

Smith, Bradford. Large Animal Internal Medicine. 2nd Edition. Mosby. 1996. Pp. 814-817.

Symptoms: diarrhea, discharge, fever, mouth infection

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