Bluetongue virus protein structure. Molecular model of some of the protein structures found in the protein coating of the bluetongue virus (BTV). This model shows the secondary protein structure, with helices and arrowed sheets indicating the protein shapes. This virus causes bluetongue disease, a disease of sheep and (more rarely) other ruminants such as cattle and deer. It is named for the swollen blue tongue it causes in affected animals. It is spread by midges. This image shows protein chains from the VP3 and VP7 core proteins. Numerous protein chains like these make up the much larger icosahedral protein coat of the virus. The viral genetic material is contained inside this protein coat.