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About Bluetongue

Definition

Bluetongue is a disease of animals affecting all ruminants, including sheep, cattle, deer, goats and camelids (camels, llamas, alpacas, guanaco and vicuña). It does not affect horses or pigs. Although sheep are most severely affected, cattle are the main mammalian reservoir of the virus and are very important in the epidemiology of the disease. It is characterised by changes to the mucous linings of the mouth and nose and the coronary band of the foot. The disease is caused by a virus spread by certain types of biting midges. Bluetongue is present when it is confirmed by laboratory tests that the Bluetongue virus (BTV) is circulating in an area. Bluetongue does not affect humans.

History and spread of the disease

Bluetongue was first described in South Africa but has since been recognised in most countries in the tropics and sub-tropics. (For details of countries where Bluetongue is present see details from OIE website. Since 1999 there have been widespread outbreaks of Bluetongue in Greece, Italy, Corsica (France) and the Balearic Islands (Spain). Cases also occurred in Europe in Bulgaria, Croatia, Macedonia, Kosovo and Yugoslavia. Serotypes 2, 4, 9 and 16 have been involved. These cases have been well north and west of its normal distribution. It appears that the virus has spread from both Turkey and North Africa.

Bluetongue has never previously been recorded in Great Britain.

Bluetongue in Europe

Bluetongue serotype 8 (BTV-8) was first found in the Netherlands, Belgium, Luxembourg, Western Germany and in parts of North Eastern France in Summer/Autumn 2006. In 2007, Northern Europe experienced a dramatic increase of new cases in all existing infected areas, and cases numbered into the many tens of thousands as disease steadily spreads across Europe. Affected countries witnessed increased mortality rates in animals and production losses, which caused severe economic hardship for the farming industry. Affected countries began vaccination programmes in 2008, but as expected, disease has now re-emerged, As of 18 November 2008 France have so far this year reported over 23,000 cases of BTV8 and over 3,500 cases of BTV1.  The Dutch  have so far reported 55 BTV8 infected premises during 2008 and BTV1 in four animals imported from France.  They also reported the first case of bluetongue virus (BTV) serotype 6 in Europe on 24 October 2008. Tests have confirmed the presence of virus in four cows on four premises.

For the latest information on Bluetongue outbreaks in Europe, please see the relevant presentations from the Standing Committee on the Food Chain and Animal Health (SCoFCAH). Outbreaks of other serotypes of Bluetongue have also been declared. A map of the existing restriction zones of the countries affected by Bluetongue is available here.

Reporting disease

Animal keepers should remain vigilant for the clinical signs of the disease in sheep and cattle, and as ever practice good biosecurity. Bluetongue is a notifiable disease and must be reported to your Division Veterinary Manager.

Cause

Bluetongue is caused by a virus within the Orbivirus genus of the family Reorvirades. At present 24 distinct serotypes have been identified as a result of serum neutralisation tests.

The virus is transmitted by a small number of species of biting midges of the genus Culicoides. Bluetongue virus cannot naturally be transmitted directly between animals. Virus transmission between animals occurs via these midges. However, the likelihood of mechanical transmission of the virus between herds/flocks and within a herd/flock by unhygienic practices (e.g. use of contaminated surgical equipment or hypodermic needles) cannot be excluded.

When a midge bites an infected animal, the virus passes to the midge in the blood meal and the virus multiples in the midge. The cycle of replication of the virus in the insect vector and in the ruminant host, results in amplification of the amount of BTV available to uninfected naive hosts and vectors.

Peak populations of vector Culicoides occur in the late summer and autumn and therefore this is the time when Bluetongue is most commonly seen.

Confirmation of Bluetongue disease

Under internationally agreed guidelines (OIE) Bluetongue is unusual in that the disease is only confirmed when there is evidence that the virus is circulating between animals and vectors in an area.

What estimate has Defra made of the maximum and average distance a midge infected with bluetongue disease can travel?

The species of Culicoides midge which has acted as a vector for disease in the current North European outbreak, are different from the species which have traditionally acted as the vector in Southern Europe and Africa. The European Food Standard Agency are currently conducting a detailed epidemiological analysis of the North European outbreak, including details of vector biology and behaviour.

From initial studies it can be roughly estimated that a midge can travel up to 1.5 – 2 km a day in a local area. However, if caught in suitable meteorological conditions midges can be carried much farther distances, especially over water masses i.e. more than 200 km. All of these details are an approximation and vary according to local environmental, topographical and meteorological conditions.

Contingency Planning

We are required under the terms of the Directive to have a contingency plan approved by the Commission. The plan follows a standard format and provides a broad overview of what will take place during an outbreak. The contingency plan (PDF 43 KB) is available for download.

Further information

 

Page last modified: 1 December, 2008

Department for Environment, Food and Rural Affairs