10/11/2022:  Thanks to a very alert sheep farmer, the extremely infectious jaagsiekte sheep retrovirus (JSRV) was detected in the Netherlands in 2021. This virus causes lung tumours and is not a compulsory notification disease. It is essential that the Dutch sheep population is kept free from this infectious disease. The symptoms can resemble those of the Maedi/visna virus (MVV).

In 2021, a Dutch breeder of Scottish Blackface sheep purchased an MVV-free, older ram in order to boost the genetic diversity of his flock. The ram came from Scotland and was tested again for MVV on arrival. Following a quarantine period, the ram mated the sheep farmer’s eight ewes. The animal subsequently developed respiratory problems. Following three unsuccessful courses of antibiotics, the breeder contacted the Veekijker. The description and the country of origin resulted in very cautious alarm bells being sounded. The animal was euthanised and submitted for necropsy.

Pathological examination

At first sight, the sick ram’s lungs resembled those of animals suffering from Maedi/visna virus. However, microscopic examination at GD showed no sign of inflammation. The pathologist did however find an infiltrating tumour, which began in the epithelial cells of the lung. This is also known as an adenocarcinoma and is a sign of jaagsiekte. Lung tissue was sent to the Moredun Research Institute in Scotland, with whom GD has worked for many years, for verification purposes. There, an expert in the field of this disease applied a specific immuno-histochemical colouration test, and indeed confirmed infection with the JSRV.

Under the radar

Jaagsiekte is caused by the JSRV, a disease known by a number of names. Jaagsiekte has an incubation period ranging from months to years and can therefore remain hidden for a long time. Infected animals transmit the virus via the frontal airways, even before they display any clear clinical signs. An affected animal suffers respiratory problems due to growing tumours, which often produce copious fluids. The respiratory problems are often worsened by secondary bacterial infections. At an advanced stage, jaagsiekte can sometimes be distinguished by raising the animal by its hind legs (wheelbarrow test). This often produces copious amounts of watery nasal discharge. In this case, the alarm bells sounded upon describing the clinical signs, as well as the country of origin of the ram and contacts within the network of specialists at the European College of Small Ruminant Health Management. There is no medication or vaccination against JSRV. GD advises that infected animals be culled, as well as any animals who may have been in contact with them.

We needed absolute certainty

Dirk Jan Beumer: “As a breeder of Scottish Blackface sheep, we had spent the past year searching high and low for new blood for our flock of eight ewes. We have been breeding these sheep for decades now, and we purchased a good, older, MVV-free, genotype ARR ram from a renowned breeder in Scotland, in order to avoid inbreeding.

In order to be absolutely certain, we also arranged for a blood test for Maedi/visna virus (MVV) directly upon arrival of the ram. Following a quarantine period, the ram soon mated all the ewes. Sometime later, the ram developed a strange cough, which we had never seen in our Blackfaces. As the cough worsened, we consulted with our veterinarian and decided to give a course of antibiotics to prevent pneumonia. While the ram initially improved, he started coughing again two weeks later. I personally expected this to be a form of resistance to the first course of antibiotics. The ram once again initially improved after the second course, but became short of breath and started coughing again after a few days. A third course was therefore administered without any lasting results.

As the animal was visibly deteriorating, we had him put out of his misery and submitted him to GD for examination. At that point, I suspected that there was something seriously wrong. Pathological examination seemed to be the best option to get certainty for the rest of the flock and for the sale of healthy offspring.

Once the ram had been definitively diagnosed as having jaagsiekte, we culled the ewes who had been in contact with the infected ram. In order to save their lambs, we separated them from the ewes at birth and bottle raised them.”

These signs were not in keeping with a bacterial infection

Stephen van der Raaf, veterinarian: “On my first visit, I couldn’t help noticing the lovely build of the newly purchased Blackface ram. It was only after longer observation that the animal proved to be somewhat short of breath. My colleagues had already tested him for Maedi/visna virus (MVV) and treated him for a lung infection. The clinical signs of Maedi/visna virus were particularly fitting with the symptoms: a somewhat lacklustre animal with rapid breathing. On physically examining him, I heard left-side raspy breathing and established a marginally increased body temperature.
Maedi/visna virus (MVV) had already been excluded and the limited effect of the first course of antibiotics surprised me. The diagnosis was therefore probably a bacterial lung infection. Resistant Mannheimia bacteria came to mind. A second course of antibiotics combined with dexamethasone seemed to have more effect and was therefore extended. However, the sheep farmer was not convinced and requested that I check the ram again. The animal had indeed not recovered. His condition had deteriorated slightly, but he was otherwise reasonably stable. These were not clinical signs of a bacterial infection, in which you see either normal recovery or serious deterioration.

Following a last course of antibiotics, the ram remained breathless, but without any other symptoms. As we did not believe further treatment to be useful, we decided to await any further developments. If the ram were to deteriorate, the advice was to submit it for necropsy following euthanasia. Two weeks later, I was faced with a completely different animal. Emaciated, lethargic and with severe nasal discharge. These new symptoms were suggestive of clinical signs already discussed with my colleagues, namely jaagsiekte. Necropsy by GD and further examination in Scotland confirmed that diagnosis.”