LESS than a year after the first cases of the Schmallenberg Virus were confirmed in the UK, farmers are facing another potentially deadly threat to their sheep flocks
A virus that causes emaciation in sheep usually between three and four years of age could be devastating for farmers if allowed to spread, according to vets.
Johne’s Disease is more commonly known and tested for in cattle, but according to Iain Carrington, of Intake Veterinary Services, Hexham, this may be the reason that it is so under- diagnosed in sheep.
In sheep, infection causes a severe gastric condition leading to emaciation usually without the chronic diarrhoea seen in cattle and poor wool growth. In affected flocks the cull rate can be as high as 5-10%.
Johne’s is spread by eating food or water contaminated with faeces, although infection can also occur in the womb and via the milk.
Goats can be a source in the spread of the disease, but the role of cattle and rabbits is also likely. The condition is usually noted at between three and four years of age but can be seen as early as one year.
According to Mr Carrington, the condition is further worsened as a result of its difficult diagnosis.
He said: “Diagnosis is complicated as symptoms are not specific and on-farm post-mortem examination is difficult and unlikely to be conclusive, often with concurrent problems overshadowing the underlying disease.
“Laboratory testing is also problematic. Direct microscopy on stained faecal samples is unreliable and culture takes a minimum of eight weeks and often much longer.
“Serological testing can detect approximately 60% of cases of which 95%0plus are positive. This means that if they are positive they are most likely to be infected but only two-thirds of the infected animals are likely to be detected.
“Non-specific tests such as albumin and globulin levels provide the most useful tests for screening sheep with chronic weight loss.
“Sheep with Johne’s Disease have a very low albumin level and a normal globulin concentration. This can be useful when screening a group of poorly-performing sheep and point to a diagnosis.”
The lack of a reliable specific laboratory test in the live sheep makes planning an eradication scheme difficult, although any cases that are identified should be culled.
Treatment is impractical as attempts have proven unsuccessful and symptoms have reappeared once the treatment has stopped.
Vaccination offers the prospect of long-term control, but is unlikely to cure a flock of disease.
Vaccine is only available through a vet as it requires a special import licence and farmers are advised to consult closely before deciding to go down this route as there can be complications.
Mr Carrington added: “This is a ‘hidden’ disease with far-reaching consequences affecting welfare and production, which is very likely under- diagnosed in UK flocks.
“Suspect cases should be checked for appropriate nutrition, good appetite, worms, dental problems and other chronic diseases to rule out the other main causes of poor bodily condition.”