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Bluetongue virus

I. General Information

1. NCBI Taxonomy ID:

2. Disease:

Bluetongue disesase

3. Introduction

Bluetongue disease or catarrhal fever is a non-contagious, non-zoonotic, insect-borne, viral disease of ruminants, mainly sheep and less frequently cattle, goats, buffalo, deer, dromedaries and antelope. It is caused by the Bluetongue virus. There are no reports of human transmission. Although the tongues of human patients with some types of heart disease may be blue, this sign is not related to bluetongue disease. Bluetongue is caused by the pathogenic virus, Bluetongue virus (BTV), of the genus Orbivirus, is a member of the Reoviridae family. There are 24 serotypes. It is transmitted by a midge, Culicoides imicola and other culicoids. Major signs are high fever, excessive salivation, swelling of the face and tongue and cyanosis of the tongue. Swelling of the lips and tongue gives the tongue its typical blue appearance, though this sign is confined to a minority of the animals. Nasal symptoms may be prominent, with nasal discharge and stertorous respiration. Some animals also develop foot lesions, beginning with coronitis, with consequent lameness. In sheep, this can lead to knee-walking. In cattle, constant changing of position of the feet gives bluetongue the nickname "The Dancing Disease". Torsion of the neck (opisthotonos or torticollis) is observed in severely affected animals. Not all animals develop symptoms, but all those that do lose condition rapidly, and the sickest die within a week. For affected animals which do not die, recovery is very slow, lasting several months (Wiki: Bluetongue).

4. Microbial Pathogenesis

The pathogenesis of BTV infection is similar in sheep and cattle and, most probably, all species of ruminants. However, there are marked differences in the severity of disease that occurs in different ruminant species or breeds after BTV infection, and infection of the same species or sheep breed with different virus strains. After cutaneous instillation of BTV (by inoculation or through the bite of a BTV-infected Culicoides vector) the virus travels to the regional lymph node, where initial replication occurs. The virus then is disseminated to a variety of tissues throughout the body, where replication occurs principally in mononuclear phagocytic and endothelial cells, lymphocytes and perhaps other cell types. Viraemia is highly cell associated and may be prolonged but not persistent in domestic ruminants. BTV promiscuously associates with all blood cells during viraemia, thus titres of virus in each cell fraction are proportionate to the numbers of each cell type; specifically, BTV is quantitatively associated most with platelets and erythrocytes and, because of the short lifespan of platelets, virus is largely or exclusively associated with erythrocytes late in the course of BTV infection of ruminants. BTV infection of erythrocytes facilitates both prolonged infection of ruminants and infection of haematophagous insect vectors that feed on viraemic ruminants, and infectious virus can co-circulate for several weeks with high titres of neutralizing antibody (Maclachlan et al., 2009).

5. Host Ranges and Animal Models

Bluetongue infects ruminants, mainly sheep but also cattle, goats, buffalo, deer, dromedaries, and antelope. It is transmitted by a midge, Culicoides imicola and other culicoids (Wiki: Bluetongue).

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