VANCOUVER — Ovine progressive pneumonia is known by many names, but the results of this slow, viral infection are always the same.
It invades the white blood cells of a sheep and slowly kills the animal.
It is estimated that 36 percent of sheep operations and 24 percent of all animals tested in the United States are infected with this virus.
“It is really a burden on U.S. sheep producers,” said Mike Heaton of the U.S. Department of Agriculture’s Animal Research Service.
The disease was first described about 150 years in Texel sheep, and numerous strains affect sheep and goats around the world, Heaton told the World Congress on Genetics Applied to Livestock Production, which was held in Vancouver Aug. 17-22.
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The chronic lung infection, which is also called Montana sheep disease, thin ewe syndrome or Visna/Maedi virus, leads to muscle wasting and eventually affects the mammary glands, leg joints, lymph nodes and central nervous system.
It is transmitted primarily among adult ewes during lambing by respiratory secretions or from the ewe to the lamb through infected colostrum. The virus is then replicated in the white blood cells.
As the science of genomics progressed, researchers speculated that some sheep may be more susceptible than others.
A study that examined thousands of sheep to see how they became infected discovered that a Type I membrane protein known as TMEM154 seems to be the connection.
“Our working hypothesis is TMEM154 is some sort of cellular doorway for the OPP virus to facilitate infection,” he said.
“We didn’t have direct evidence supporting this hypothesis, but all the evidence we have so far seems to be consistent with this,” he said.
Managing genetic variation in the TMEM154 gene may help reduce and then eradicate the virus in affected flocks.
Researchers looked at infected ewes that were five or six years old and found that sheep with one or two copies of this protein were much more susceptible to infection.
They also typed the virus and found that different forms of the disease exist around the world. There also appeared to be a connection be-tween these different types and certain strains of sheep.
The study bred a group of infected ewes last fall and are now monitoring the lambs.
A commercial blood test is already available to see if individuals carry TMEM154 and its variants. It costs $10 to $12 per test.
Heaton advised producers in areas where the virus is found to sample the oldest ewes to measure prevalence within a flock. Serological and genetic testing, as well as management strategies, may be appropriate in infected flocks to rapidly decrease the prevalence of infection.
Producers with flocks free of disease may consider testing to avoid introducing it and to select animals less likely to become infected.
