alphavirus /al′favī″rəs/ , any of a group of very small Toga viruses consisting of a single molecule of single-stranded ribonucleic acid within a lipoprotein capsule. Many alphaviruses multiply in the cytoplasm of cells of arthropods and are transmitted to humans from mosquitoes, such as those causing equine encephalitis and Semiliki Forest virus. See also encephalitis, Toga virus.
