11 November 2008

5 minute read

Midges carry the bluetongue virus and infect cattle through their saliva
Photo: Defra

The journey of this complex non-enveloped virus begins with a host species of midge. The midge, travelling at an estimated average of 1.5 to 2 kilometers a day, infects cattle through its saliva. Once inside, the virus multiplies in the regional lymph nodes and spreads into the blood. As the amount of BTV available to uninfected hosts increases, the cycle of contamination keeps turning - the journey goes on.

Previously it was thought that the virus would be unable to survive in the cooler climates of Europe, but since 1999, there have been outbreaks in Greece, Italy, Corsica, Balearic Islands, and as far north as the Balkans.

Today, bluetongue is one of the most serious animal health issues affecting Europe. Each year it continues to spread, causing severe disease among the affected animal population and wreaking economic havoc for those farmers afflicted.

In 2006 BTV8 was believed to have adapted to temperate host midges and survived the ensuing winter. At that point came the realisation that the problem was here to stay. Many believe that rising global temperatures caused by greenhouse gas emissions are to blame for the emergence of exotic viruses and diseases such as bluetongue, but the virus has many potential inlets.

One concerning hypothesis to how the virus managed to survive the tough European winter was put forward by scientists at the Institute for Animal Health. They reported that three cows that had recovered from bluetongue last Autumn were exported from Holland to Northern Ireland in January 2008.

In February, these cows gave birth to calves that were found to be carriers of the disease. If BTV is capable of transplacental infection of the ruminant foetus, this will add a whole new dimension to the problem. Midges could then spread the disease from the calves to other animals, starting a new season of infection in a new area, or country.

Image: Europa

To make matters worse, genetic analysis performed at the Institute for Animal Health's Pirbright Laboratory this year confirmed the discovery of a new viral strain never before seen in Europe. The BTV6 strain was detected on three farms in Holland. This means that six strains of bluetongue are currently active in Europe.

According to another report by the Institute of Animal Health, the sequence of gene 2 of the BTV-6 from the Netherlands was more than 99.9% the same as gene 2 of a live BTV-6 vaccine produced in the Republic of South Africa. "This led to speculation that the source of the BTV-6 in the Netherlands might be illegally imported vaccine", said the report. To date, only inactivated BTV vaccines are licensed in Europe.

Each new strain of bluetongue requires a specific vaccine. As countries get around to vaccinating against one type of strain another one looms on the horizon. So what does all this mean for the farmer?

The economic implications of bluetongue to date are difficult to assess. A spokesperson for the UK Department for Environment, Food and Rural Affairs (DEFRA) said, "When the initial incursion of the disease took place in September 2007, the country was subject to movement controls resulting from the outbreak of FMD. We have estimated that the overall cost to the farming industry resulting from FMD controls in 2007 was £100 million."

It is not just the loss of animals and veterinary cost of an outbreak that costs the farmer, but the restrictions imposed on movement over large areas. If an outbreak is confirmed, animals within a one hundred kilometer radius of the incident are confined within a protection zone. Animals cannot leave these zones until the virus is eradicated. Consequently, farmers are prevented from taking their cattle to market.

The presence of the virus has also had a considerablly adverse effect upon international trade, as countries free from bluetongue attempt to maintain that status.

Vaccination is Key

Experience gained from controlling the disease has shown that strict movement restrictions and vaccination are the most effective prevention and control tools, as is also the case for other animal diseases, summarised a report from the World organisation for animal health (OIE).

Referring to the potential economic effects and costs of control measures, Mr Gediminas Kirkilas, Prime Minister of the Republic of Lithuania , stated: “Prevention is better than cure”, reiterating the motto of the European Union Animal Health Strategy 2007–2013, which fully complies with OIE strategies.

Vaccination is the only real prevention strategy. This spring, an awareness campaign was launched in the UK, urging farmers to order enough vaccine to protect their cattle against the bluetongue virus. As a result, 2008 has seen no disease circulation of bluetongue in the UK so far.

The "Don't Hesitate - Vaccinate!" campaign was spearheaded by the National Farmers Union and funded by the regional development agency, SEEDA, in the South East. Thousands of postcards and posters were distributed in an attempt to get the voluntary vaccination programme underway. Meanwhile, in Scotland, there is now a bluetongue helpline (0845-155-3366).

"Successful vaccination will result in minimal economic impact of disease. However, vaccination incurs a cost to those farmers that choose to vaccinate their stock," said a Defra spokesperson.

In the UK, vaccines cost around 55-66p per ml plus VAT for a 50ml bottle, around 82-98p per ml plus VAT for a 20ml bottle and around 66-79p per ml plus VAT for a 100ml bottle.

There is no easy solution. Bluetongue is a vector-borne disease, spread by midges, and is therefore difficult to control. There are several BTV serotypes present in Europe, and the key concerns are the BTV-1, 6 and 8 serotypes. Unless the prevalence of BTV-1 and BTV-8 in particular is reduced through widespread vaccination in affected countries, all countries in the EU are bound to remain at risk.

Further Reading

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You can visit our Bluetongue information page by clicking here.

November 2008