MV threat is real warns top SAC vet

By andrew arbuckle
Published on 11/07/2012 02:13

Sheep farmers may have largely dismissed the threat of a highly infectious exotic disease that entered this country some 40 years ago, but yesterday the results of a Great Britain wide survey showed the number of flocks infected with Maedi Visna (MV) virus has doubled in the past 15 years.

In addition to revealing that 2.8 per cent of all flocks in 
this country are now infected with the viral disease – for which there is no cure – the survey also found that the number of infected sheep has increased four-fold.

With the infected flocks, the level of infection has increased from 13 per cent to 24 per cent, with an extreme case of more than 80 per cent also being picked up by the survey, carried out jointly by the Scottish Agricultural College and the Animal Health and Veterinary Laboratories Agency.

Speaking yesterday on the findings, SAC vet Catriona Ritchie said that it was present across the country, with hot spots down in Leicestershire and Gloucestershire. In Scotland, the survey had picked up positives in both the Ayr and Inverurie SAC animal health catchment areas.

She stressed that, although the survey had looked at more than 11,000 blood samples from more than 700 flocks, it was still a relatively small sample and may have missed another known hot spot in the Scottish Borders.

Maedi Visna, which is a combination of two Icelandic words meaning “heavy breathing” and “brain disease”, came into this country in the 1970s through the importation of sheep from the continent, where the disease is endemic.

Visible signs of MV are not usually seen until about half of the adult flock is infected and these can take up to ten years to become apparent, giving rise to Ritchie’s concerns that the disease may be more widespread than is currently realised.

The key signs are loss of body condition, poorer fertility, mastitis, increased twin lamb disease, smaller and weaker lambs born, leading to increased mortality. A lower volume of and poorer quality colostrum and milk can lead to reduced lamb growth rates.

In heavily infected flocks, an increased number of deaths in adult sheep are usually reported, often due to a secondary Pasteurella pneumonia.

Ritchie’s SAC colleague, Brian Hosie, stressed that MV was not a disease that affected humans and added that continued 
efforts had to go into preventing the disease getting into the 
nation’s flocks.

“My advice is to purchase unaffected sheep and use the scheme to keep infection out,” said Hosie. “Producers should be aware if the symptoms and be ready to discuss any problem with their vet.”

But it was admitted the best option in some cases might be culling infected sheep.