Scientists Tackle Livestock Virus

Research on the malignant catarrhal fever virus leads scientists to the first step in developing a vaccine.

by Dani Yokhna
Courtesy USDA/ Peggy Greb
Scientists found can track the life cycle of a the virus that causes malignant catarrhal fever, a disease found in sheep, cattle, pigs and other animals.

Scientists at the USDA’s Agricultural Research Service have pinpointed the life cycle of a virus in sheep that causes malignant catarrhal fever, leading them to the first step in developing a vaccine for that disease.

Prior to this discovery, vaccine development for malignant catarrhal fever was stymied because the virus wouldn’t grow in cell culture. Now that scientists understand these viral changes, they can begin to find the right cell types to grow the virus, says Hong Li, a microbiologist who contributed to the disease’s research.

Malignant catarrhal fever is caused by a virus that’s usually transmitted among animals such as bison, cattlepigs and sheep. The virus undergoes several changes inside of the animal’s body, targeting specific cell types at different stages of its own life cycle, according to the research provided by Li, ARS veterinary medical officer Naomi Taus, Lindsay Oaks at Washington State University and Donal O’Toole at the University of Wyoming.

The process the virus follows is called “cell tropism switching.” The viral replication in sheep is divided into three stages: entry, maintenance and shedding.

Virus Entry
The virus enters the sheep through the sheep’s nasal passages and reaches the sheep’s lungs, where the virus replicates.

Virus Maintenance
The virus then infects the sheep’s lymphocytes, a type of immune cell that circulates through the sheep’s whole body. During the maintenance stage, the virus stays in the sheep’s lymphocytes and rarely replicates. This type of infection is referred to as a “latent infection.”

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Virus Shedding
During the shedding stage, the virus reactivates from the infected lymphocytes and targets specific cells in the sheep’s nasal area to complete its replication. The virus is then shed through the sheep’s nasal secretions.

According to experts at Iowa State University, while signs of malignant catarrhal fever in animals may never appear in animals, symptoms include:

  • fever
  • depression
  • weakness
  • diarrhea
  • trouble breathing
  • nasal and ocular discharge
  • crusting around the muzzle, mouth, udder and teats
  • possible sudden death

If you suspect malignant catarrhal fever in one of your livestock, separate the animal from the rest of the herd and consult a veterinarian who can test for the disease. The disease is reportable in many states. Contact your state veterinarian for more information specific to your area.

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