Loss of bluetongue-free status would hit livestock trade
Sheep are the species most commonly associated with bluetongue and tend to be the hardest hit, but cattle can also be significantly affected.
The latest threat to livestock farms may be blowing in on the wind.
“The most likely way it actually got into the country is probably by a midge being blown across from the UK,” said veterinary surgeon Dr John Donlon during a recent Teagasc podcast discussion on bluetongue.
“If a midge can get blown across the Irish Sea, then there’s a strong possibility it could be blown right down the country, or from one farm to the next, so there is a strong risk of it spreading.”
In dairy cows, one of the key symptoms of bluetongue is a sudden drop in milk yield.
“The swelling of the lips and tongue — particularly in sheep — are the really obvious signs,” Dr Donlon explained. “The virus attacks the blood vessels, causing them to leak, and that leads to oedema in the lips and tongue. You may also see drooling and sores on the face.”
Lesions may also appear on the claws and feet. “It affects fertility as well, so animals can potentially abort or produce deformed foetuses,” he said.
Farmers are advised to consult their vet if animals appear unwell, but Dr Donlon said suspected bluetongue cases should also be reported to the Department of Agriculture. “Animals can be sub-clinically infected, meaning they don’t necessarily show very clear clinical signs," he said.
He added that all animals in a bluetongue outbreak are likely to go through a recovery period, during which weight gain is reduced. “Fertility would be the area for both suckler and dairy herds that would concern me most.”
Sheep are the species most commonly associated with the disease and tend to be the hardest hit, but cattle can also be significantly affected. Deer, alpacas, llamas and other cloven-hoofed animals are also susceptible.
“Cattle replicate the virus quite a lot, so they can effectively ‘hypercharge’ the virus,” Dr Donlon said.
He noted that the timing of infection may limit the extent of spread.
“Midges are most active between April and November, and the virus replicates within the midge when temperatures are above 12°C. From a time-of-year perspective, this would typically be the end of the bluetongue season.”
“If we get a prolonged period of cold temperatures, that will certainly reduce the spread,” he said.
“The hope would be that the infected midge population dies over the winter, although there is a concern that the virus could overwinter in some midges.”
If an outbreak were confirmed, Dr Donlon said a 20km control zone would likely be established. “Within that zone, movements of susceptible animals would not be allowed, except in very exceptional circumstances that would need to be pre-approved by the department. The only routine exception would be animals moving directly to slaughter.”
“There would be no trading of animals outside that control zone. Marts would still be able to operate, and farmers in areas without a confirmed outbreak would still be able to trade.”
However, he warned that Ireland would lose its bluetongue-free status. “International trade with other bluetongue-free countries would be restricted and would require certification of animals’ health status.”
Dr Donlon also cautioned that rams and bulls could become infected and subsequently infect their offspring, with risks extending to semen and embryos.
“Try to avoid purchasing semen from areas where there is known bluetongue infection,” he advised. “Even with testing, there is a possibility that an animal could become infected and shed the virus but still be missed.
“Keep a very close eye on your animals, and if you have any doubts at all, contact the Department of Agriculture,” he said. “If we catch an outbreak very early, there is a strong possibility we can contain it.”
