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Bluetongue virus(BTV) is a double stranded RNA virus belonging to the family of reovirus and the genus of circovirus. Its genome consists of 10 fragments, and the virus particles have a symmetrical icosahedral structure. The outer capsid is composed of VP2 and VP5 proteins, and it is divided into 24 serotypes with weak cross immunity. Viruses have strong stability in dry environments, but are sensitive to high temperatures and acidic conditions. The virus is mainly transmitted through the bite of Culicoides and its host is ruminants. Sheep have the most significant symptoms after infection, manifested as high fever, oral ulcers, and swollen hooves, with a mortality rate of 20% -90%. Cattle often have latent infections, but they can be transmitted vertically through the placenta or semen. The pathological features are multiple organ bleeding and necrosis caused by vascular injury. Prevention and control mainly rely on vaccination, including attenuated and inactivated vaccines, while also requiring a combination of pest control measures and quarantine culling.
Figure 1. Structure of Bluetongue Virus. (Roy, Polly,et al, 2009)
The virus is a circular particle with a nucleocapsid diameter of 53-60nm. The capsid consists of 32 large shell particles with a diameter of 8-11nm. The virus is a symmetrical icosahedron. BTV contains double stranded RNA, consisting of 10 fragments with a molecular weight of 19 × 106, accounting for 20% of the total weight of the virus. The G+C content is 42% to 44%. The virus contains seven structural peptides, with the main core protein being VP3, which wraps around three secondary proteins VP1, VP4, and VP6, as well as double stranded RNA fragments. VP7 is another major protein located outside the subnucleus, and the outer capsid is composed of two major proteins, VP2 and VP5. BTV can survive for a long time in dry serum or blood, sometimes up to 25 years, or in decaying blood. The virus can survive for about 4 months in recovered animals.
The pathogenicity of BTV is a direct result of complex molecular interactions between viral proteins and host cell mechanisms. After infection through mosquito bites, the virus initially replicates in local lymph nodes and then spreads through the bloodstream, targeting vascular endothelial cells and lymphocytes. The resulting vascular damage can lead to characteristic symptoms such as bleeding, edema, and tissue necrosis. Recent studies have revealed the complex mechanism by which BTV evades the host's innate immune response, which is crucial for its ability to establish infection. The following table summarizes the key viral proteins and their interactions with specific host pathways and genes.
| Viral Protein | Category | Key Host Target/Pathway | Function in Pathogenesis |
| VP6 | Structural (Inner Core) | Viral ssRNA | An RNA-binding protein and helicase essential for genome packaging. It facilitates the transport of single-stranded RNA genomes into the assembling viral capsid. |
| NS3/NS3A | Non-structural | cGAS-STING pathway, STAT2 | A multifunctional viroporin critical for virus release. It acts as a potent interferon antagonist by inducing the autophagic degradation of cGAS and STING (key DNA-sensing immune proteins), and also promotes the degradation of STAT2 to block interferon signaling. |
| NS4 | Non-structural | JAK-STAT pathway | Another interferon antagonist that inhibits both the induction and signaling of type I interferon (IFN-I), further suppressing the host antiviral state. |
BTV is one of at least 22 recognised species in the genus Orbivirus, belonging to the wider Sedoreoviridae family. It is a complex, non-enveloped virus which has a double stranded RNA genome consisting of ten segments of different sizes. These segments encode its seven structural proteins (VP1-7) and five non-structural proteins (NS1-5). The BTV particle has an icosahedral structure, which consists of three layers including the outer capsid, core and sub-core. Due to its segmented genome, BTV can reassort, swapping genome segments, when two BTV strains replicate within the same cell. This can give rise to new BTV strains, which can have different characteristics, and potentially virulence, which may make current vaccines ineffective.There are at least 29 recognised serotypes of BTV, with strain diversity observed within each serotype. BTV serotypes 25-29 are considered ‘atypical’ as they are not spread by Culicoides biting midges, but can spread via contact, typically they do not cause clinical disease.
Blue tongue virus mainly infects sheep, with a latent period of generally 5-12 days. It usually develops significantly 6-8 days after infection, manifested as fever of 39-42 ℃, which can be maintained for 6-8 days, mental exhaustion, loss of appetite, excessive salivation, oral mucosal congestion and edema, or manifested as necrosis and ulceration of the oral mucosal surface, pharyngeal edema, purple swelling of the lips and tongue, and edema that can extend to the neck and chest. The hoof crest is congested and the swollen area is painful, causing limping, and often leading to bloody dysentery due to gastrointestinal lesions. The severity of the disease depends on the secondary infection and the condition of the sheep's body. The course of disease is generally 6-14 days, the incidence rate is 30-40%, and the mortality is 20-30%, sometimes as high as 90%. Most of them die of pneumonia or gastroenteritis and other complications. Cattle, goats, and other ruminant animals have mild symptoms and generally have a benign course. Infected sheep can also have their fur broken or even completely shed, seriously affecting the quality of wool and meat products. Pathological changes are mainly seen in the mouth, rumen, heart, muscles, skin, and hooves.
The diagnosis of BTV combines clinical observation and laboratory confirmation.
| Diagnosis | Details |
| Molecular technology | Reverse transcription polymerase chain reaction (RT-PCR) is the primary method for early and sensitive detection of viral RNA and determination of serotypes. |
| Serological techniques | Antibody testing is crucial for monitoring and confirming past contact. Recombinant bluetongue virus antigens, especially VP7, are the core of modern serological diagnosis. Recombinant VP7 antigen is expressed in insect cells and other systems infected with rod-shaped viruses for indirect ELISA (iELISA). These detection methods have high sensitivity and specificity (over 98%) in detecting population specific antibodies against all BTV serotypes in sheep and goat serum, making them highly valuable for large-scale screening. |
The bluetongue virus still poses a significant threat to global animal health and livestock economy. The pathogenesis depends on detailed molecular interactions, where viral proteins such as NS3 and NS4 systematically disrupt host immune defenses, such as the cGAS STING and JAK-STAT pathways. The advancement of diagnostic technology, especially the use of recombinant VP7 antigen in sensitive serological testing, has greatly improved monitoring capabilities. Future efforts to mitigate the impact of this disease will be combined with ongoing research on viral biology, development of next-generation vaccines, robust monitoring based on advanced diagnostics, and adaptive vector control strategies in the face of climate change.
Reference
| Target | Cat. No. | Product Name | Host | |
| Bluetongue virus | DAG-WT5801 | Recombinant Bluetongue virus antigen [His] | E. coli | Inquiry |
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