5 serotypes of BTV in the U.S. - BTV2, 10, 11, 13, & 17 The bluetongue viruses (BTV) and the epizootic hemorrhagic disease viruses (EHDV) are closely related serogroups of orbiviruses. Worldwide there are at least 24 serotypes of BTV and 10 serotypes of EHDV. Five serotypes of BTV (2, 10, 11, 13, and 17) exist in the US but only 10, 11, 13, and 17 are known to cause disease. Two serotypes of EDHV (1 and 2) exist in the US and both are known to cause disease.
2 serotypes of EHDV in the U.S. - EHDV1 & 2


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This is a negative stained preparation of EHDV viewed by transmission electron microscopy. The BTV and EHDV are 65-80 nm in diameter, are nonenveloped, and are characterized by a double capsid structure. The genome consists of 10 segments of double stranded RNA. Note the ring-shaped capsomers of these core particles. These structures are the reason for the term orbivirus (the prefix orbi- means ring or circle).

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