Rabbit hemorrhagic disease (RHD), also known as viral hemorrhagic disease (VHD), is a highly infectious and lethal form of viral hepatitis that affects European rabbits. Some viral strains also affect hares and cottontail rabbits. Mortality rates generally range from 70 to 100 percent. The disease is caused by strains of rabbit hemorrhagic disease virus (RHDV), a lagovirus in the family Caliciviridae. Rabbit hemorrhagic disease virus Rabbit hemorrhagic disease virus (RHDV) is a virus in the genus Lagovirus and the family Caliciviridae. It is a nonenveloped virus with a diameter around 35–40 nm, icosahedral symmetry, and a linear positive-sense RNA genome of 6.4–8.5 kb. RHDV causes a generalized infection in rabbits that is characterized by liver necrosis, disseminated intravascular coagulation, and rapid death. Division into serotypes has been defined by a lack of cross-neutralization using specific antisera. Rabbit lagoviruses also include related caliciviruses such as European brown hare syndrome virus. RHDV appears to have evolved from a pre-existing avirulent rabbit calicivirus (RCV). Nonpathogenic rabbit caliciviruses related to, but distinct from RHDV, had been circulating, apparently harmlessly, in Europe, Australia, and New Zealand prior to the emergence of RHDV. In the course of its evolution RHDV split into six distinct genotypes, all of which are highly pathogenic. The three strains of rabbit hemorrhagic disease virus of medical significance are RHDV, RHDVa and RHDV2. RHDV (also referred to as RHDV, RHDV1, or as classical RHD) only affects adult European rabbits (Oryctolagus cuniculus). This virus was first reported in China in 1984, from which it spread to much of Asia, Europe, Australia, and elsewhere. A few isolated outbreaks of RHDV have occurred in the United States and Mexico, but they remained localized and were eradicated. In 2010, a new lagovirus with a distinct antigenic profile was identified in France. The new virus, named (abbreviated as RHDV2 or RHDVb), also caused RHD, but exhibited distinctive genetic, antigenic, and pathogenic features. Importantly, RHDV2 killed rabbits previously vaccinated with RHDV vaccines, and affected young European rabbits, as well as hares (Lepus spp.). All these features strongly suggest that the virus was not derived from RHDVa, but from some other unknown source. RHDV2 has since spread to the majority of Europe, as well as to Australia, Canada, and the United States. Epidemiology and transmission Both viruses causing RHD are extremely contagious. Transmission occurs by direct contact with infected animals, carcasses, bodily fluids (urine, feces, respiratory secretions), and hair.