Bluetongue’s arrival in the UK in the autumn of 2007 came at a relatively fortuitous time. The disease’s peak transmission season was coming to an end and vaccines for BTV8, the strain of bluetongue which was found in Suffolk, were being developed by a number of pharmaceutical companies.
This lucky combination of factors meant the disease never got a foothold in the UK, with a relatively low number of cases diagnosed in late 2007 and vaccines becoming available in spring 2008 just ahead of the peak activity for the culicoides midge, the insect responsible for transmitting the disease from animal to animal.
And these vaccines were also particularly effective at helping stop the disease in northern Europe where it had a devastating effect in many countries, including The Netherlands, Belgium and France, although it wasn’t until 2010 that France got the disease under control properly.
Since June last year the UK has been in a lower risk zone for bluetongue, meaning that while there have been no cases of the disease in the UK since 2008 farmers have been able to continue vaccinating to protect their stock, explains NFU chief livestock adviser John Mercer.
“At the moment there are discussions in Brussels for EU legislation to be changed, so that the UK could declare itself disease free and still be able to vaccinate. Under the current rules a disease-free country can’t vaccinate.
“But with the chance of infection moving quickly through Europe as we’ve seen with BTV8, it would make sense to have the ability to vaccinate as a protection measure should BTV emerge in northern Europe again. We’re hopeful this change will be made ahead of the 2011 vector season in May.”
So, with winter 2010 surveillance showing no signs of BTV8 circulating and the UK likely to be declared disease free later this year what should be UK farmers’ policy for the disease in 2011?
According to independent sheep vet Paul Roger, the need for vaccination against BTV8 in 2011 is nil, with the disease not thought to be present in the UK and the risk of it arriving from mainland Europe low.
“The perceived risk of the disease arriving in the UK from continental Europe is much lower than it has been for several years. Therefore, vaccination is no longer a priority.
“In some ways this is fortunate, but in others it could present a false sense of security. With reduced demand for vaccine in both the UK and continental Europe, production will slow and this will lower the level of preparedness should there be another outbreak of the disease.”
However, Mr Mercer reminds farmers that the only way to be sure of protecting their stock is to vaccinate. “The present risk level is low, but vaccinating your livestock is the only true way of being sure you won’t see infection on your farm.
“The main concern is that vaccination programmes in many northern European countries, particularly France, are now moving from compulsory to voluntary, so we need to watch carefully what happens this summer.”
But as the next incursion in to northern Europe could be from any one of a number of strains of bluetongue and the vaccines are strain specific, continuing to vaccinate against BTV8 wouldn’t offer any protection against other strains, such as BTV1, BTV9, BTV11 and BTV16, all of which are active in southern Europe, explains Mr Roger.
“What must be maintained is vigilance and sero-surveillance of unusual disease outbreaks. With increasing globalisation and international trade movements, the UK must become more aware of the potential threat from exotic disease. Farmers should report any unusual disease incidence to Animal Health.”
It is essential to remember some exotic diseases, such as bluetongue can easily be misdiagnosed as other more common ailments. Indeed, the early signs of bluetongue could easily be mistaken for photosensitisation or orf.
Mr Roger believes now more than ever there is a pressing need for livestock farmers to have active farm health plans in place. “A farm health plan in which you record the incidence of various diseases is essential. It means you know what diseases are present on your farm and how many cases of each you normally see. Then when you see something unusual you are more likely to recognise it as being abnormal and do something about it.”
And while BTV8 may no longer be an immediate threat to UK livestock, he says this is thanks to vaccination programmes both here and in continental Europe. “It is safe to say all strains of bluetongue are under control in northern Europe. But, should BTV8 or any other strain become a threat again farmers should not hesitate to vaccinate.”
BLUETONGUE IN EUROPE
Cases of bluetongue were low in Europe in 2010, with Italy reporting 24 cases of BTV1, BTV2, BTV4, BTV8 and BTV9, France reporting just one case of BTV1, Portugal reported two cases of BTV1 and Spain had five cases of BTV1 and BTV4.
Imports and exports
One of the highest risk ways of the disease arriving in the UK in recent years has been its arrival with imported animals. A number of cases have been detected in post-import testing of both cattle and sheep since early 2008, but the UK’s confluent disease status with the rest of the infected countries of the EU has meant it has been impossible to ban imports from other infected countries.
Instead imported animals arriving from a BTV protection zone must be naturally immune or vaccinated. To certify this they have been subject to both pre- and post-movement testing, although the post-movement testing has been relaxed in recent times so that testing is undertaken on a risk-based system, explains Mr Mercer.
“A move to a disease-free status would mean similar rules for imported stock with all stock imported from higher risk areas having to be immune to the disease. Being disease free would also further reduce surveillance costs in the UK as there would be no need for routine surveillance to take place.”
Post-movement testing is not being done based on an assessment of the following criteria, the BTV status of the country of origin and the level of midge activity in the country of origin which would vary by season. There will also be random tests prioritising animals perceived to be at higher risk.
But, while Mr Roger acknowledges the reduced risk imports now pose, he questions whether imports, particularly of dairy heifers, need to be made in any volume. “Anyone who is considering importing stock to the UK from northern Europe should be extremely vigilant. Ensure animals are tested for bluetongue before they leave their country of origin and they should be vaccinated against the disease, too.”
Once imported, all stock should be subject to rigorous quarantine on the farm of arrival, he says. “Preferably the quarantine period should be six weeks of isolation in facilities which prevent contact with any resident stock. This allows enough time for all relevant tests to be completed and for the incoming stock to be examined regularly for any visual or physical sign of disease.
“It also allows the incoming stock to be exposed to the pathogens already present on the farm before being mixed with resident stock.
For those exporting stock, a possible move to disease-free status would make exports easier and free up trade with Northern Ireland, adds Mr Mercer. “Although, bearing in mind the premium likely to be earned from exporting stock, the extra cost of administering the vaccine would have been negligible anyway.”
What is bluetongue?
Bluetongue is a midge-transmitted virus which can kill up to half of infected sheep and about 1% of infected cattle.
What insects are involved?
Culicoides obsoletus and pulicaris midges carry the disease and can infect animals through a single bite.
What are the symptoms?
In sheep the symptoms can include, eye and nasal discharges, drooling, high body temperature, swelling in mouth, head and neck, lameness and wasting of muscles in hind legs, haemorrhages into or under skin, inflammation of the coronary band, respiratory problems, fever and lethargy.
And in cattle the symptoms include, nasal discharge, swelling of head and neck, conjunctivitis, swelling inside and ulceration of the mouth, swollen teats, tiredness, saliva drooling and fever.