Plea to be aware of forgotten disease

The English Beef & Lamb Executive, Eblex, and its Welsh equivalent, have clubbed together with the all-UK Animal Health and Veterinary Laboratories Agency to commission a big survey to establish the extent of Maedi Visna – suspecting that it might be more prevalent than most farmers think.

The show-going public will be aware of MV – without knowing what it is, in most cases – because since about 1996, every sheep competition has had segregated areas for animals from MV-accredited flocks, meaning those which have been declared free of MV and are signed up to take precautions against buying in infected animals.

The disease is named in Icelandic because it was in Iceland that it was first identified, in 1954, although it has probably been endemic for much longer in mainland Europe – especially where sheep are housed together, for milking. It is also known in the USA, as Montana Sheep Disease.

It was probably imported into the UK 30 years ago, along with Continental bloodstock, and Continental breed societies have led the way in trying to stamp it out. The disease takes time to develop into a problem and a lot of commercial lamb producers, turning over stock fast, never see any sign of it and tend to think it is not worth worrying about.

According to the British Texel Society, MV is often not noticed until 50 per cent of a flock is infected, creating a weight of viral presence which is reflected in the severity of the symptoms – breathing problems and general wasting, which will eventually lead to death. It has been compared to AIDS in humans, although there is no obvious relationship – and no human health risk has been found to be likely.

However, ewes can be short of milk and producing slow-growing lambs long before they are obviously ill.

A small survey in 2002 found at least some sheep infected in one flock in 30. There are grounds for suspecting it has spread since then and the Scottish Agricultural College, which got the contract to run MV testing and flock accreditation back when Defra was Maff, has been commissioned to go through 20,000 blood samples collected from all over the country for an annual survey for brucellosis. Its usual charge, for members of the accreditation scheme, is £2.50 a test.

Welcoming the initiative, British Texel Society chief executive John Yates said: “Most of the pedigree flocks in the (MV control) scheme already maintain excellent bio-security. The industry on the other hand has very little idea of the amount of MV virus circulating outside the scheme and within the commercial sector. Improving control of this disease will aid in the efficient production of lamb meat – assisting the industry with climate change targets, by removing issues related to poor flock productivity. This disease can easily creep up on flocks due to its subclinical nature. It is in the interests of everyone in the UK sheep industry to have a firm indication of the level of MV infection.”

There is no vaccine and infection lasts for life. It took Iceland 30 years to eradicate MV through culling. It is passed around in breath vapour and the biosecurity measures include keeping accredited sheep at least two metres away from any untested animals.

Catriona Ritchie, a vet working for the SAC’s Sheep & Goat Health Schemes, said this week: “We talked to one owner of 1500 Mule ewes who estimated MV had cost him £30,000 to £50,000 over a couple of years in productivity losses.”