Malignant Catarrhal Fever in a 1-year-old heifer
By R. Gayman Helman, DVM, PhD, Guy Sheppard, DVM, and Meagan Schroeder, PhD
A 1-year-old heifer became weak and isolated herself. Three days later, the heifer was examined by the submitting veterinarian and was described as being lethargic and having a drooped head, oculonasal discharge, conjunctivitis/scleritis, mild mucosal petechiations, and frank blood in the urine. The cow was weak and ataxic and would fall down and get back up frequently. The heifer’s temperature at presentation was 103°F. Treatment with florfenicol and oxytetracycline, vitamin B-12, dexamethasone, and IV fluids was administered. Treatment with oral and IV fluids was repeated the next day, and bilateral corneal edema and hypopyon were noticed. The heifer continued the process of stumbling, falling down, and getting back up and died the following day.
A variety of fresh and fixed tissues were submitted to the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) for diagnostic testing. Histopathology was pursued initially. Lesions were noted in a number of organs including brain, liver, kidney, spleen, tongue, forestomachs, abomasum, intestines and urinary bladder. There were early perivascular accumulations of lymphoid cells in the brain. The liver and kidney both had multifocal lymphoid infiltrates and vasculitis was identified in the spleen and kidney. There were erosions and ulcerations affecting mucosal surfaces on the tongue and forestomachs and extensive ulceration of the bladder mucosa.
Additional testing utilizing PCR technology for Malignant Catarrhal Fever (MCF) and Blue Tongue (BT) viruses followed. BT virus was not detected, but MCF was positive with a ct value of 28.40.
MCF is caused by viruses of the Macavirus genus that are in the Herpesviridae family (Gammaherpesvirinae subfamily). Two major groups of MCF viruses include one that primarily affects exotic even-toed ungulates and one in sheep, goats, and white-tailed deer. The viruses are named after the reservoir host which serve as carriers. Of these, the most common types in the United States are the sheep-associated virus and the wildebeest-associated virus. The sheep virus is the most common source of the virus in the United States, but with the increased appearance of exotic ungulates, the wildebeest-associated virus has also been identified as a cause of disease in cattle.
The disease is normally fatal in cattle which are a dead-end host for either the sheep- or wildebeest-associated viruses. The lymphoid infiltrates and proliferation may be so severe, that nodes may look like lymphoma. MCF is easily transmitted horizontally between reservoir and non-reservoir, susceptible hosts. However, there is no apparent horizontal transmission between a sick bovine and other healthy cattle. Separation of cattle and sheep or cattle and reservoir exotic ungulates is advisable and the best mode of prevention. There are no commercially available vaccines.
Differentials for MCF include bovine viral diarrhea (BVD), BT, and rinderpest, a foreign animal disease. In cattle dying from disease appearing to be consistent with MCF, a broad sampling of tissues exhibiting gross lesions to include both fresh and fixed samples will provide the best opportunities for definitive identification. This would include ulcerative lesions, enlarged lymph nodes, and organs such as liver, kidney, lung, heart, spleen, and brain.
- Center for Food Safety and Public Health, Iowa State University College of Veterinary Medicine, Malignant Catarrhal Fever (http://www.cfsph.iastate.edu/Factsheets/pdfs/malignant_catarrhal_fever.pdf )
- The Merck Veterinary Manual (http://www.merckvetmanual.com/)