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Disease factsheet: Bluetongue

Bluetongue latest situation

If you suspect signs of any notifiable disease, you must immediately notify a Defra Divisional Veterinary Manager.

Definition

Bluetongue is a disease of animals affecting all ruminants, including sheep, cattle, deer, goats and camelids (camels, llamas, alpacas, guanaco and vicuña). 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. 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 been recorded in Great Britain.

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 the insect vector; some species of 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.

Clinical signs

Bluetongue - Guidance for livestock keepers (PDF)Clinical signs can vary by species - although symptoms are generally more severe in sheep, cattle can occasionally show signs of disease. Cattle are important in epidemiology of the bluetongue as they act as an often silent source of BTV – a reservoir for disease and keep the infection circulating. It is important to be vigilant, especially in the case of sheep. If you suspect any signs of the disease you must report this immediately to your local Animal Health Office.

Leaflet: Bluetongue - Guidance for livestock keepers Adobe acrobat pdf file (1 MB)

Clinical signs in sheep:

  • Eye and nasal discharges
  • Drooling as a result of ulcerations in the mouth
  • High body temperature
  • Swelling of the mouth, head and neck
  • Lameness
  • Haemorrhages into or under the skin
  • Inflammation at the junction of the skin and the horn of the foot – the coronary band
  • Respiratory problems – difficulty with breathing and nasal discharge
  • A blue tongue is rarely a clinical sign of infection
  • Deaths of sheep in a flock may reach as high as 70 per cent. Animals that survive the disease can lose condition with a reduction in meat and wool production.

    • Clinical signs in cattle: It is possible that cattle will show no signs of illness, however clinical signs have included:

  • Nasal discharge
  • Swelling of the head and neck
  • Conjunctivitis (runny eyes)
  • Swelling in, and ulceration, of the mouth
  • Swollen teats
  • Tiredness
  • Saliva drooling out of the mouth
  • In cattle, the disease cannot be diagnosed on clinical grounds and requires laboratory testing for confirmation.
  • The disease can only be confirmed by laboratory tests.

    In cattle, the disease cannot be diagnosed on clinical grounds and requires laboratory testing for confirmation. Photos of clinical signs...

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.

Legislation and disease controls

The Bluetongue Regulations 2008 came into force on 26 April 2008, this implements council directive 2000/75/EEC concerning the control and eradication of Bluetongue.  The Regulations revoke the Bluetongue Order 2007 apart from article 17 which provides for the slaughter powers under the Animal Health Act 1981 to be retained.  In Scotland, Wales and Northern Ireland similar legislation also exists.

Controls

The default measures set out in legislation are aimed at preventing disease spread (through for example restriction of animal movement and through vector mitigation measures). Broadly, the controls can be summarised as follows:

  • Veterinary investigation on suspect premises, and restrictions which includes a ban on movement of susceptible animals on and off the premises.
  • On Confirmation that bluetongue virus is circulating, restrictions remain in place and are extended to a zone of 20km radius around the infected premises (IP).
  • Wider zone(s) must also be declared:
    • A Protection Zone (at least 100km radius around an IP) and a Surveillance Zone (at least 50km in radius beyond the PZ); or
    • A single PZ of at least 150km.
  • Movement of susceptible animals out of these zones are banned (although animals can move freely within those zones) and we must implement surveillance programmes.
  • There is some flexibility in demarcating the zones (with Commission agreement), but various factors such as local geography must be taken into account.

The vector-borne nature of the disease (and distribution of vectors) ensures that the risk of disease spread can only be mitigated against to a limited degree (i.e. we cannot guarantee 100% protection from vectors).

The benefits of housing animals at times of the day when the midge vector is most active are unproven (at least in the context of species of midges transmitting BTV8 in Northern Europe). Treatment of midge breeding grounds e.g. manure heaps as well as using repellents and approved pour-on insecticides on cattle and sheep may reduce the risk of infection to some degree in certain circumstances.

In partnership with industry, we will be issuing guidance on the likely effectiveness of such measures. Emphasis should also be made to avoiding the use of contaminated surgical instruments or hypodermic needles.

As Bluetongue is spread via vectors (i.e. midges), rather than from animal to animal, compulsory slaughter of ruminants infected with bluetongue would not normally form part of our control strategy.

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 Adobe acrobat pdf file (43 KB) is available for download.

Related Pages

See also

Page last modified: April 3, 2009

Department for Environment, Food and Rural Affairs