Sheep farmers may help treat human disease

21 July 2000

Sheep farmers may help treat human disease

By Shelley Wright

SCOTLANDS sheep farmers could help in the development of vaccines for crippling human lung diseases such as cystic fibrosis.

Mike Sharp, a virologist at the Moredun Research Institute, says that sheep farmers willingness to donate animals they suspected of having jaagsiekte disease, a viral in-fection of the lungs, is vitally important to the international research now underway.

"We have never been able to grow the virus that causes jaagsiekte, so farmers donating animals to us has been abs-olutely vital," says Dr Sharp.

He says the disease produced symptoms of chronic pneumonia in adult sheep. But the typical sign that allowed diagnosis of jaagsiekte, which results in a large tumour in the lower part of the lungs, was that fluid would run from the nose of an infected animal if its head was pushed down.

As well as seeking a solution to the disease for sheep farmers, research could also lead to a treatment for human lung diseases such as cystic fibrosis, Dr Sharp adds.

The retrovirus causing jaagsiekte attacks cells in the lungs that produce surfactant, the substance that keeps the lungs inflated. Sufferers of cystic fibrosis, a genetic condition, cannot produce enough surfactant because of the damage to their lung cells. So there is widespread interest, especially from human biology research teams in the US, in the work being done on jaagsiekte at the Moredun.

There is the potential, Dr Sharp says, for the jaagsiekte virus to be used in gene therapy treatment of cystic fibrosis sufferers; carrying corrective genes into the surfactant-producing lung cells.

A recent survey of sheep at veterinary investigation centres in Scotland had identified jaagsiekte in about 20% of cases. "But although its a common disease, the infected sheep do not produce any immune response so we have no diagnostic test," he sys.

"All we can advise is that farmers remove any sheep they suspect to have the disease, and that really is not a satisfactory position to be in."

Jaagsiekte is contagious. And one of the main problems is that the diseases progress is often so slow that infected animals are often not easily identified until they are two to three years old – leaving plenty of time for them to infect others in the flock.

However, in the past five years resear-chers had discovered that the virus, as well as being in the tumour cells, can also be found in the lymph nodes of infected animals. "So we can detect the virus in blood," saysDr Sharp. "But unfortunately the virus seems to be present only in about one in 250,000 blood cells, so actually finding it is the equivalent of trying to find one person in a crowd of 6m."

He remains hopeful, however, that a vaccine for sheep is possible. The lack of immune response in infected animals shows the jaagsiekte virus is somehow managing to switch off the sheeps immune response.

The challenge would be to try to isolate the proteins causing this, then efforts could be made to develop a vaccine to allow the immune system to destroy the virus. &#42

Researchers are hoping to develop a vaccine for jaagsiekte virus in sheep.

&#8226 Chronic pneumonia symptoms.

&#8226 No diagnostic test.

&#8226 Contagious; slow development.

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