Life Cycle of Blue Tongue Virus

Life cycle of the Bluetongue Virus

Bluetongue viruses are generally found within the latitudes 40°N to 35°S  (from 

Southern Spain to Southern Africa), although during the current outbreak the virus spread as far as 53°N. 

Bluetongue is caused 
by a virus within the Orbivirus genus of the family Reoviridae.  24 distinct serotypes of the virus have been identified. (shown by the Figure on the left)

The bluetongue virus is made up of three layers. In the centre is the nucleic acid (the genetic blueprint) which carries all the information needed to  make more copies of the virus. This is surrounded by two layers, each made up of two proteins. There is a further outer coat that is lost when the core moves into an animal cell.

The BTV RNA is packaged inside two protein layers (pictured on the left). A third layer is lost when the virus enters the host cell.










Pathogenesis and Duration of *Viremia

fig. A The transmission cycle of bluetongue virus (BTV)
fig. B  The life cycle of the Culicoides vector


The extrinsic incubation period of BTV involves the entry of virus into the Culicoides vector, dissemination through the *haemocoel and subsequent infection of the salivary glands. Temperature affects most stages of the Culicoides life cycle, including the survival of adults and larvae through the winter months (enhanced by high winter temperatures), recruitment to the adult population and activity rates of adult Culicoides. Most stages of the Culicoides life cycle are also affected by the availability of moisture. Breeding habitats are semi-aquatic — larvae and pupae require moist habitats and adults are prone to *desiccation.


The cattle are implicated as the asymptomatic reservoir hosts of the virus, they do not get the disease but is able to produce the virus. The sheep are "target" species, they suffer from the disease. The virus co-circulates with the sheep's antibodies.

Bluetongue Blight-er

Biting Midge (Culicoides obsoletus)

Biting midges act as vectors of important livestock diseases. The biting midge Culicoides obsoletus is believed to transmit the bluetongue virus. This virus, now widespread throughout Europe, causes a potentially fatal disease of ruminants (sheep, goats, cattle and deer) but cannot be transmitted directly between animals, only via the midges. The midges can, in suitable weather conditions, be carried more than 200 km in air currents and this is probably how the disease was recently introduced into the UK. Bluetongue poses a serious threat to livestock production in Europe and it’s all because of these midges!




* - definitions taken from http://dictionary.reference.com/


viremia - presence of virus in the blood


ruminant - any even-toed, hoofed mammal of the suborder Ruminantia,being comprised of cloven-hoofed, cud-chewing quadrupeds,and including, besides domestic cattle, bison, buffalo, deer,antelopes, giraffes, camels, and chevrotains


haemocoel - the body cavity of many invertebrates, including arthropods and molluscs, developed from part of the blood system


desiccation - to preserve by removing moisture ; dehydrate