Dean's Lunchtime Clinical Club - 21 November 2017 - Alison Lee
The final Clinical Club of the semester took place on 21 November. The session was chaired by the Dean, Professor Michael Doherty, with Alison Lee, Resident in Anatomical Veterinary Pathology, presenting on Virus-Induced Lung Tumours in Irish Sheep. Alison has recently completed a research project on Ovine Pulmonary Adenocarcinoma (OPA), a contagious tumour of the lungs of sheep which is caused by Jaagsiekte sheep retrovirus (JSRV).
Alison began by explaining that OPA affects 2 - 4 year old sheep, occurs almost worldwide, and can cause 30 – 50% mortality when initially introduced to a flock. It's spread through aerosol and colostrum transmission and the lack of an adaptive immune response limits the capabilities of diagnosis. Alison added that Dolly the Sheep contracted this disease and was ultimately euthanised as a result.
Alison went on to describe the clinical signs of the disease, which can present as a 'chasing sickness;' the animal experiences respiratory difficulties and looks like they’ve been running. They can also suffer from coughing, crackles, fluid from the nose and weight loss. Alison then went through the pathology of OPA, and described the lungs as enlarged, heavy, oedematous, with well-demarcated, dark, purple/grey areas. Histopathology includes cuboidal or columnar cells and connective tissue stroma.
In terms of diagnostics, PCR on blood samples is not sensitive enough. PCR on BAL fluid is laborious and misses early cases. Necropsy is the most commonly used diagnosis and this helps farmers know if it’s in their flock. A saliva test is currently being developed. There is no treatment for this disease and it's controlled through a slaughter policy; biosecurity will also help in this regard.
Alison then spoke about her project and why she decided to research this area. OPA is a notifiable disease, with Irish prevalence/distribution unknown; it also affects a high quality agricultural export. The purpose of the project was to confirm the presence of OPA/JSRV in Ireland and to estimate prevalence and geographical distribution.
In total, lungs from 1911 adult sheep were available to the study, with 369 undergoing further examination; sheep from 18 counties were examined and 17 counties were sampled from. There were variations in the numbers sampled/examined between counties, and Alison added that this is to be expected in 'real world research.' 31 animals tested positive for the virus – 1.6% of the total examined. 10 were positive for OPA tumours, with 4 non OPA tumours also found.
The study concluded that JSRV and OPA are present in Ireland, with a relatively wide geographical distribution; there is potentially a higher prevalence in the North. They also found that non OPA lung tumours can occur and that infected sheep don’t always have tumours. Alison also explained that abattoir surveys may cause biases in results.
There were lots of questions following on from Alison's presentation, with one student asking if there was a link between the prevalence of the disease in Scotland and Northern Ireland. Alison stated that there had been a lot of cases in Scotland and the North of England historically, and that while there was possibly a link due to trade, this hadn't been proven. Michael outlined that the first report of OPA on the island of Ireland was in 1985 in Tyrone, and that there tend to be more cases in the North. He added that there's a lot of movement of sheep from Scotland to the North, and that this creates a real biosecurity issue.
Questions were also asked around control procedures and Alison noted that there's no national control programme; the disease is problematic for individual farmers. Michael outlined that there's no blood test for this disease and that it's a big issue at farm level, and as you can’t test for it, it's very challenging for vets to deal with.
Many thanks to Alison for presenting such an interesting and informative talk on this recently completed research project.