Bluetongue virus

Bluetongue virus (BTV) infects all ruminants, including cattle, sheep, goats, along with wild animals like buffaloes, deer, antelope and camels.

BTV is spread mainly by biting midges (Culicoides), but other biting insects may also transmit the virus. There is evidence that certain serotypes (BTV-8) can be transferred from a ruminant mother to her foetus during pregnancy. It could also be spread by contaminated objects such as needles or surgical equipment.

BTV is present in many parts of the world including Europe, the Middle East and North Africa.

Bluetongue is a notifiable disease and should be reported. For the latest information on the bluetongue situation in the UK and how to spot and report, please visit gov.uk.

Virology

BTV belongs to the family Reoviridae, genus Orbivirus with 20 recognised species in the genus. It is a complex non-enveloped virus with a capsid and double stranded RNA genome consisting of 10 segments of different sizes.

Clinical signs

Certain breeds of sheep are most likely to show severe clinical signs of BT. Severity of BT varies with the strain of BTV and host animal breed and species. Cattle and deer are less likely to show signs but act as important ‘reservoirs’ of virus.

Clinical signs:

  • Fever
  • Reddening of the mucosal membranes
  • Sores on the nose, gum and dental pads
  • Swelling of the face, lips and tongue
  • Lameness
  • BT can lead to death and can cause abortion or deformities in lambs or calves
  • The “blue tongue”, from which the disease gets is name, is not frequently seen. Animals may also develop breathing difficulties if the tongue swells.

Pirbright's research on bluetongue virus

There is no treatment available other than supportive therapy. Outbreaks can be controlled through vaccination of susceptible animals. Due to work carried out at the Institute, the UK was able to vaccinate large numbers of livestock in 2008 against serotype 8, which prevented huge economic losses and the death of lots of animals.

The difficulty in combatting BT is that infection or vaccination of an animal with one serotype does not confer immunity to any of the other serotypes. It is virus protein 2 (VP2), located at the surface of the virus, that both determines the serotype and activates immune responses. Vaccines exist for just a few of the serotypes, so knowing the serotype of BTV that is causing a given outbreak is important.

In November 2023, a single animal infected with BTV serotype 3 was detected in the UK. 

Improving diagnostics is a key area of research the Institute participates in. The gene that encodes VP2 of 24 serotypes has now been sequenced, and a test has been developed to identify them (using PCR). These tests are much more rapid than conventional virus neutralisation tests, giving results within a day rather than three weeks or so. 

At the Institute we investigate how Culicoides biting midges transmit BTV between animals. We monitor the activity of adult midges across the UK at key times in the year to understand when disease transmission may be possible. We simulate likely BTV spread according to weather conditions and time of year. 

Research papers

Pascall D J, Nomikou K, Breard E, Zientara S, Filipe A D S, Hoffmann B, Jacquot M, Singer J B, De Clercq K, Botner A, Sailleau C, Viarouge C, Batten C, Puggioni G, Ligios C, Savini G, van Rijn P A, Mertens P P C, Biek R, Palmarini M (2020)

PLoS Biology 18 (4) , e3000673
Rajko-Nenow P, Golender N, Bumbarov V, Brown H, Frost L, Darpel K, Tennakoon C, Flannery J, Batten C (2020)

Microbiology Resource Announcements 9 (10) , e01539-19
Rajko-Nenow P, Christodoulou V, Thurston W, Ropiak H M, Savva S, Brown H, Qureshi M, Alvanitopoulos K, Gubbins S, Flannery J, Batten C (2020)

Viruses 12 (1) , 96
Publisher’s version: https://doi.org/10.3390/v12010096
Flannery J, Batten C (2019)

Veterinary Practice September , 36-37

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