Maedi Visna on the rise in Scottish sheep flocks

Many Scottish sheep flocks could be threatened by a rise in the incurable viral disease Maedi Visna (MV), according to veterinarians working with the Scotland’s Rural College (SRUC).

They warn that testing has identified a worrying number of infected flocks, suggesting that infection is spreading throughout Scotland’s sheep sector.

“Farmers have started to heed our previous warnings about the disease,” said SRUC Veterinary investigation Officer Lynn Gibson.

“Flockowners have taken the opportunity to screen their animals using the current MV diagnostic test package.”

In most cases, screening was performed in flocks where there were suspicions of MV infection and in 23% (seven of the 31 of the flocks tested) these suspicions proved to be correct. The owners of six of these flocks had reported seeing signs including breathlessness in adult sheep, lameness and swollen joints.

As signs of MV are not usually seen until around half the sheep in a flock are infected, SRUC vets believe it is likely these flocks have a high level of infection.

The name Maedi Visna derives from two Icelandic words describing the main clinical signs of pneumonia and wasting or ill-thrift. MV is a chronic disease caused by a retrovirus, introduced to the UK through imported animals. Contagious and difficult to diagnose it can lead to poor body condition; poorer fertility; increased mastitis; smaller, weaker lambs and increased deaths. There is no cure or vaccine.

According to Lynn Gibson MV has a long incubation period “This means the clinical signs can take years to develop by which time one single animal can have spread infection through the flock.

“The first indications of a problem can include an increase in barren ewes or the numbers of thinner sheep meaning more are being culled from the flock as unproductive,” she said.

“Sheep never develop immunity to MV and with no effective treatment or cure the only option with heavily infected flocks is to depopulate and restock from reliable sources,” says Lynn.

The Department of Agriculture, Food and the Marine has confirmed that Ireland is free from MV. Imports of sheep from England, Wales or Scotland must be accompanied by a supplementary health certificate issued by an official veterinarian providing a number of additional guarantees for freedom from MV.

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