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Vets concerned at rise in Maedi Visna (MV)

Published 29th January 2015 | Article by Rhian Price (Farmers Weekly)

Vets concerned at rise in Maedi Visna (MV)

Vets from Scotland’s Rural College believe many commercial sheep flocks could be at threat from a rise in the incurable viral disease maedi visna (MV).

SRUC’s testing has identified a “worrying” number of infected flocks, which suggests infection is spreading, vets say.

Diagnostic testing was carried out in 31 UK flocks where MV infection was suspected. The disease was confirmed in 23% (seven) of these flocks.

The owners of six of the flocks had reported seeing signs of the disease. Signs of MV are not usually seen until about half the sheep in a flock are infected due to its long incubation period, so SRUC vets believe it is likely these flocks have a high level of infection.

Maedi visna

MV is a chronic disease caused by a retrovirus. It was introduced to the UK through imported animals. It is highly contagious and difficult to diagnose. There is no cure or vaccine.


  • Poor body condition
  • Poorer fertility
  • Increased mastitis
  • Smaller, weaker lambs
  • Increased deaths
  • Breathlessness in adult sheep
  • Lameness
  • Swollen joints

Read how one flock was devastated by MV

SRUC veterinary investigation officer Lynn Gibson, based in St Boswells, says: “Clinical signs can take years to develop, by which time a 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.

“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 Ms Gibson.

She adds: “We recommend any flock owners that find they have ewes which have lost condition since tupping time should check for MV. It is something to take seriously, not ignore. Disease in sheep flocks reduces productivity and income in a sector already operating on narrow margins.”

Concerned flockmasters should target-test 12 older, thinner animals using the MV diagnostic test to indicate if losses are due to the disease. A similar approach should be taken to sheep showing illthrift or those that react badly to exercise.