Caliciviridae is a family of viruses, members of Class IV of the Baltimore scheme. They are positive-sense, single stranded RNA which is non-segmented. There are currently seven species in this family, divided among 5 genera. Diseases associated with this family include: feline calicivirus: respiratory disease; rabbit hemorrhagic disease virus: often-fatal hemorrhages; norwalk group of viruses: gastroenteritis. Caliciviruses naturally infect vertebrates, and have been found in a number of organisms such as humans, cattle, pigs, cats, chickens, reptiles, dolphins and amphibians. The caliciviruses have a simple construction and are not enveloped. The capsid appears hexagonal/spherical and has icosahedral symmetry (T=1 or T=3) with a diameter of 35–39 nm.