Over three-quarters of ewes in a flock that were diagnosed with Jaagsiekte during an ultrasound scan turned out not to have the fatal disease at all, a new study has found.
The highly contagious disease causes cancerous lung growths in sheep, which leads to coughing, severe body condition loss and, in the latter stages of infection, discharge from the nose.
Jaagsiekte is also known as OPA and ultrasound scanning to identify lesions in lungs is the only means of diagnosing the disease in live sheep.
In a new study, which was led by Dr Peers Davies from the University of Liverpool, a flock of 1,074 ewes were scanned by a vet who had training and experience in finding OPA lesions. Overall, 51 ewes were diagnosed with the disease at scanning and were culled.
The highly contagious disease causes cancerous lung growths in sheep
However, during post-mortem examination, OPA lesions were identified in only 24% of the culled ewes. The presence of the disease in these ewes was later confirmed by laboratory testing of infected tissue.
The researchers found that in 35% of the culled ewes, there were lung abnormalities which were caused by other respiratory issues, such as abscesses, lungworm, or pneumonia. They do not recommend culling ewes due to the presence of these types of lesions, as there is no evidence of “a clinical, productive or economic benefit”.
The remaining 41% of the culled ewes in the study had no detectable lesions of any kind at post-mortem.
The researchers found that in 35% of the culled ewes, there were lung abnormalities which were caused by other respiratory issues, such as abscesses, lungworm, or pneumonia
The research paper, which was published in Veterinary Record, recommends not using ultrasound scanning to find OPA lesions in flocks where sheep have no symptoms, or risk of Jaagsiekte is likely to be low.
However, the researchers acknowledge that ultrasound scanning can have a role as “a useful, additional diagnostic tool” when investigating sheep with respiratory symptoms or evidence of ill thrift.
They also recommend that vets who scan for OPA lesions check their work regularly by getting post-mortem examinations carried out on as many of their positive cases as possible.