The onset of spring and the imminent promise of vaccination have drawn bluetongue into focus again, Jonathan Long reviews the UK disease situation.

Warmer days may be just the boon flagging grassland needs this spring, but they are also the one thing that will encourage the spread of bluetongue disease across the UK as midge activity and virus replication step up a gear.

Bluetongue is the quiet killer, arriving unannounced on the wind with the midges and striking quickly to affect ruminants of all shapes and sizes. Sheep, cattle, goats, llamas and deer are all at risk, although sheep are most affected by the disease and most likely to die as a consequence.

When vaccinating cattle a large fold of skin should be taken hold off and the vaccination given under this skin.
Farmers should vaccinate wherever they normally do, but the neck and over the ribs are usual places

And while some farmers believe the threat is not that large, Jules Dare of Westpoint Vet Group points to the experience of the Netherlands last year as an example of just what the disease can do. "More than 30% of the Dutch national flock had the disease last year and 6% of the country's sheep died because of bluetongue. In the cattle population 10-20% were affected, with total mortality of 1%.

"Businesses suffered losses, largely because of lost production, secondary infection, infertility, lameness, weight loss, dead animals and vet and medical costs. More than 1.35m sheep, 3.8m cattle and 280,000 goats were affected and the total economic impact is estimated to have been E81m."

Bluetongue can be difficult to spot in some species, but that is no excuse for letting your guard down and failing to keep an eye on susceptible stock. In sheep, the most common symptoms are a nasal discharge, facial swelling, including oedema under the jaw, oral ulceration and lameness or a reluctance to stand, says Mr Dare. "It can present similarly to other conditions, including pneumonia, foot-and-mouth, claw abscess polyarthritis and extreme orf. So accurate diagnosis is essential. When you suspect bluetongue or, more importantly, can't rule out bluetongue infection, contact your vet."

Bluetongue can also cause chronic arthritis, wool loss and result in increased incidence of other diseases, including pneumonia, mastitis, weight loss and lameness, explains Mr Dare. "While in cattle it can cause a long-lasting milk drop, reduced fertility, long-lasting herd lameness, increased mastitis incidence, foetal losses, calf losses and weight loss. Conjunctivitis is also a classic symptom in cattle."

But in many cases it will cause only mild symptoms in cattle and may be as little as linear erosion around the base of teats, says Dutch vet Daan Derksen. "In suckler cows, the first thing you notice may be cows not allowing calves to suckle properly. This is a sign that teats may be sore and cows are uncomfortable with calves suckling.

Treatment options

As bluetongue is a virus there is no specific therapy against the disease itself, says Mr Dare. "The animal has to cure itself supported by treatment and nursing. Supportive treatment should include long-acting non-steroidal anti-inflammatory drugs, diuretics, antibiotics and cortico steroids.

Video one: Bluetongue symptoms

"Nursing should ensure animals have access to plenty of fresh water, soft and/or moistened food, soft bedding and stock should be protected from sunlight and heat and subject to minimal stress.

"When it is not practical to move infected stock to buildings - or when buildings are unavailable - they should be given access to fields with shaded areas and good water supplies. Sheep in particular can become lame with bluetongue, so soft bedding is essential for them to avoid excessive pain."

Prevention

It can be difficult preventing bluetongue infection, but vaccination should be the first line of defence for every farmer as and when vaccine becomes available in their area. In the meantime, there are various measures farmers can employ to limit the chances of their stock being bitten by virus-carrying midges, says Mr Dare. "First, where possible, keep animals inside during early morning and early evening to avoid the periods of peak midge activity. Second, keep infected stock inside to prevent them being bitten by midges and hence passing the disease on.

"And third, and possibly most pertinent, farmers can use insecticides, either in ear tags or as pour-on fluids to repel midges, or kill them as they land on animals."

Video two: Vaccination guns explained

A trial in Germany last year found that using Butox SWISH on cattle controlled midges for four weeks, with midges killed rapidly even after a brief contact time with hair on treated animals, reports Heinz Mehlhorn, from Heinrich-Heine University, Dusseldorf. "The trial also showed that the product spread to areas prone to midge bites - the underside of the belly and other exposed areas, such as legs.

In the trial, six heifers of about 400kg were treated with 30ml of Butox SWISH, while another six were left untreated. All heifers were kept in one group and samples were taken from all animals over the next five weeks from areas prone to midge bites.

"At each sampling point, immediate paralysis of midges occurred in the treated group, with midges dying at varying intervals after that, depending on contact time and the number of days after treatment with Butox SWISH," he adds.

"For up to 28 days after treatment all midges were killed, meaning bluetongue virus would not have had time to replicate within them before they could go on and infect other animals. In the control group all midges survived."

The wool should be parted and a pinch of skin gathered up and the vaccination given under this skin.
The neck is the best place to vaccinate sheep as it avoids carcass damage if abscesses develop

Vaccination

Vaccination in England will be voluntary and farmers in the highest risk areas will have access to vaccine first. For vaccination to be effective it will need to achieve at least 80% coverage with the aim in the UK being to stop the disease in its tracks before it becomes more widespread. As wild ruminants can harbour the disease it is essential everyone vaccinates all susceptible stock.

Vaccine will be phased in across England (News, 11 April), with Scotland opting for compulsory vaccination, probably in the vector-free period this winter, and Wales undecided as to what vaccination strategy it will employ.

Where Intervet's licensed bluetongue vaccine Bovilis BTV8 is used, sheep will require one, 1ml dose, while cattle will need two, 1ml doses three weeks apart, says Intervet's livestock vet manager Alasdair King. "All doses should be given subcutaneously and revaccination two weeks before the next risk period will be needed to protect animals in future years."

Video three: Vaccination technique

To avoid abscesses developing at the site of vaccination, animals should be dry when vaccinated and the vaccination site should be as clean as is possible, he adds. "Importantly, no animals should be vaccinated with Bovilis BTV8 until they are at least one month old. So farmers may need to plan vaccination batches to cover younger lambs and calves. In the case of both lambs and calves they will need the same dose as their adult counterparts.

"But while there may be a need to vaccinate lambs and calves after the main flock or herd, open vaccine vials with vaccine remaining in them shouldn't be kept and used at a later date. Once opened the vial should be used within the next eight hours and then discarded. It is therefore essential to order vaccine in appropriate vial sizes, either 50ml or 20ml.

Swelling of the head and a rise in temperature are two of the tell-tale signs of bluetonge in sheep

"For ease and accuracy of delivery, a ready-calibrated vaccination gun is preferable as this will ensure all animals are given the correct dose. These can be fitted with a sterilising cap to clean the needle between each animal and limit the chance of other infections being passed to the next animal and also help prevent abscesses developing at the vaccination site."

When it comes to vaccinating, it is essential to remember that the vaccine has to be given subcutaneously - under the skin, explains Mr. King. "This means taking hold of a pinch of skin and injecting into it, not injecting intramuscularly or by any other method. Failure to do this could mean the vaccine won't work properly and animals won't be protected.

"Care is also needed to avoid damaging the carcass when vaccinating, so the neck is the best place to inject the vaccine. And bluetongue vaccine shouldn't be used at the same time as other vaccinations, so other vaccination courses, such as clostridial, should be completed before bluetongue vaccine is administered," warns Mr King.

Vaccination Q and A

• When will vaccine be available?
  The first batch of doses should be available in May for farmers in the protection zone.
  
• How do I get vaccine?
  It is a prescription-only medicine available from your vet. Farmers should contact their vet to be placed on a waiting list.
  
• Which species can be vaccinated?
  The initial licence is for cattle and sheep only, but other species such as goats and camelids can be vaccinated under the cascade system under the direct responsibility of a vet.
  
• What about farms outside the protection zone?
  The protection zone will be expanded gradually across England as more vaccine becomes available to allow farms outside the protection zone to vaccinate. Alternatively, it may expand due to disease spread.
  
• How long after vaccination will animals develop immunity?
  It is likely to take about three weeks for immunity to develop.
  
• Once vaccinated, can I move my stock out of the protection zone?
  No, not immediately. For farmers wanting to move stock within England this can be done after some tests (how long after vaccination depends on the test). But for movement to Wales, Scotland or elsewhere in the EU out of the protection zone it will be necessary to obtain a vet's certificate to say the animals have been vaccinated. This may mean having the vet supervise vaccination.
  
• How much will vaccine cost?
  DEFRA has recommended prices for vets based on two mark-up levels and the two different vial sizes. Where vets want to charge a 25% mark-up, vaccine will cost 55p/ml for 50ml vials and 82p/ml for 20ml vials. When they charge a 50% mark up it will cost 66p/ml for 50ml packs and 98p/ml for 20ml packs.