Warm weather increases bluetongue risk

While no one doubts the importance of bluetongue, it seems messages are mixed regarding the risks. And according to Merial Animal Health’s vet adviser Brian Rice, vaccination has become a victim of its own success.

“People don’t seem to see a risk if they haven’t seen the disease. A bluetongue outbreak can last up to five years, so just because we haven’t seen it doesn’t mean it won’t crop up,” says Mr Rice. Results of a survey taken on behalf of Merial show farmers in the north of England believe they are at lesser risk because of the cooler weather. “Although in the past this may have had some truth, climate change is having a big impact on rate of spread, with BTV8 just identified in Norway,” he says.

Since 2004 every year there has been an additional serotype incursion into Europe, but last year there were three new serotypes arriving in to Europe – BTV1, 6 and 8 – with another 18 bluetongue serotypes still known to exist, according to Mr Rice.

bluetongue vaccine 
Wating for a local outbreak before taking the decision to vaccinate is too late, so plan for bluetongue now.
“This disease is far from over and we must take action against BTV8 first as this is causing most widespread damage in the UK with a vaccine available to control it. And with 20,000 individual holdings going down with BTV8 in France last year this demonstrates the seriousness of the disease,” he says.

But it seems other diseases are registering as of higher importance than bluetongue, with farmers in the south-west regarding TB as more important. “Despite this, most farmers do seem to understand the implications of bluetongue, with abortions, loss of fertility and reduced milk yield in dairy cattle all real problems,” say Mr Rice.

“An outbreak of bluetongue would mean major financial losses, with dairy farmers recognising milk losses could be as high as 40-50%. But several factors seem to be discouraging people from vaccinating.”

Low incidence of cases, cases confined to imported animals, geographic locations and concerns regarding abortion risk and cost seem to be the main factors hindering vaccination.

“The perceived risk of abortion from vaccination is a major concern and despite vets being quick to dispel the risk, the uncertainty has still impacted on the timing of vaccination, with some farmers reluctant to vaccinate pregnant animals.

“Farmers would be naïve if they were waiting for a local outbreak before taking action to vaccinate. Vaccines take several weeks before they are fully effective, with several doses needed in cattle. So by the time bluetongue is recognised in the local area it will probably be too late,” says Mr Rice.

But as well as vaccination the advice from experts is to begin regular vector control programmes sooner, rather than later, as the milder weather brings a rise in midge activity.

Farmers should not be lulled in to a false sense of security thinking that the cold weather will have killed the midges capable of spreading bluetongue, according to Intervet/Schering Plough animal health vet manager, Alasdair King.

“It is likely some midge larvae and possibly adults too have survived February’s cold spell. It only takes a few days of daily temperatures to average above 12C for them to start breeding to large numbers, with midges at their most active at 15-30C.

Bluetongue action 

Assess risk
Plan time for vaccination
Vector control
This is worrying when the south of England has seen several days with temperatures between 9-11C recemtly. And although vaccination remains the only way to protect cattle and sheep from the virus, vector control can help reduce midge numbers helping cut the risk of BTV.

“Treating with certain insecticides can be effective against the midge helping to cut the breeding midge population. Vets in last year’s protection zone say application of an insecticide before vaccinating in May and continued monthly applications through the season also resulted in lower cases of summer mastitis and New Forest Eyes as a result,” says Mr King.

“Starting control strategies early prevents flies (including midges) building up to high levels. Insecticide use should form part of a management programme inclduing measures such as fencing of stream banks and removing midge breeding areas such as stagnant water and dung heaps,” adds Mr King.