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About the Authors:
Manjunatha N. Belaganahalli
Affiliation: Vector-borne Diseases Programme, Institute for Animal Health, Surrey, United Kingdom
Sushila Maan
Affiliation: Vector-borne Diseases Programme, Institute for Animal Health, Surrey, United Kingdom
Narender S. Maan
Current address: Department of Animal Biotechnology, Lala Laipat Rai (LLR) University of Veterinary and Animal Sciences, Hisar, Haryana, India
Affiliation: Vector-borne Diseases Programme, Institute for Animal Health, Surrey, United Kingdom
Robert Tesh
Affiliation: Department of Pathology, University of Texas Medical Branch, Galveston, Texas, United States of America
Houssam Attoui
Affiliation: Vector-borne Diseases Programme, Institute for Animal Health, Surrey, United Kingdom
Peter P. C. Mertens
* E-mail: [email protected]
Affiliation: Vector-borne Diseases Programme, Institute for Animal Health, Surrey, United Kingdom
Introduction
The genus Orbivirus is the largest of 15 genera within the family Reoviridae and currently contains 22 recognized virus species, as well as 13 unclassified or ‘unassigned’ viruses, some of which may represent additional species [1], [2], [3], [4], [5]. Many orbiviruses are transmitted by ticks or haematophagus insect-vectors (Culicoides, mosquitoes and sand flies), with a wide host range that can collectively include cattle, goats and sheep, wild ruminants, equids, camelids, marsupials, sloths, bats, birds, large canine and feline carnivores, and humans. Members of the different Orbivirus species that are currently recognised, were initially distinguished by a lack of cross-reaction in serological assays, including agarose gel immunodifusion, complement fixation and (more recently) enzyme linked immunosorbent assays (ELISA)[2].
The orbivirus genome consists of 10 separate pieces of linear double stranded RNA (dsRNA), most of which code for a single viral protein. In the case of bluetongue virus (BTV - the Orbivirus type-species) these include seven structural proteins and four distinct non-structural proteins (Seg-10 encodes two non structural proteins). The components of the virus core-particle and at least two of the non-structural proteins are highly conserved between isolates of the same Orbivirus species, showing high level serological cross-reactions in virus species/serogroup-specific assays. The nucleotide and amino acid sequences of these conserved genes and proteins (Polymerase and T2 protein) show variations that primarily reflect the virus serogroup/species. However, within each virus species, they also show variations that reflect the geographic origin of the virus isolate (topotype) [6], [7], [8], [9], [10].
In contrast, the orbivirus outer-capsid proteins (VP2 and VP5 of BTV) are more...