Maedi Visna Project

The prevalence of Maedi Visna (MV) in the commercial sheep flock in Great Britain

Project number:                73105

Lead contractor:               SAC, VLA

Start & end date:              01 February 2012 – 30 June 2012

 

The Problem:

MV is a lentiviral infection of sheep which has a significant impact on the welfare of the individual, infected sheep but also has impact at the flock level. The disease has a long incubation period and presents mainly as weight loss but can also cause pneumonia, mastitis, paralysis and occasionally arthritis.  A large survey was undertaken in commercial flocks in 1996 and indicated MV infection in 1.5% of flocks. In 2002 another exercise over 150 flocks indicated 3.3% of flocks infected. It is considered that further sampling is necessary as there has been a rise in breakdowns in accredited flocks and this could be linked to increasing levels of infection in the commercial flock.

There are no vaccines or treatments available for MV so this study does not appeal to commercial sponsors. Yet the potential risk of MV disease lowering productivity for the commercial flock is considerable. The only tool available to the Industry is supported solely through private funding at the pedigree level of the Sheep Industry through membership of the PSGHS MV Scheme.

 

Project Aims:

  • To estimate the seroprevalence of MV in adult sheep in GB.

 

Approach:

The survey will involve testing blood from adult sheep from flocks across GB which has been collected and stored by AHVLA as part of the Brucella Melitensis survey.

 

Results:

The survey has shown that there has been an almost four fold increase in the number of sheep that are estimated to be infected with MV compared to 15 years ago.  In the 1995/6 survey 0.19% of individual sheep were found to be positive, compared to 0.74% in this survey.  There are twice as many infected flocks now as then and within the infected flocks the average proportion of the flock testing as positive has doubled.  For flock seroprevalence it was 1.4% in 1995/6 compared to 2.8% in this sample.   For infected flocks the mean number of sheep that tested positive was 13.2% in 1995/6 and 24% in this survey.

 

Planned activity:

Flock owners need to be taking more action to prevent their flocks from becoming infected with MV.  This would include buying replacements from MV accredited flocks, quarantining and testing sheep before introducing them to the flock and, if possible, putting in place measures to reduce the risk of infection entering form neighbouring flocks.  Regular monitoring of the flock by blood testing a proportion for MV is also recommended because by the time clinical signs of MV are seen in a flock, infection is already at a high level making it much more difficult to put in place an effective control programme.