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​RHD is a highly contagious, fatal viral disease in rabbits caused by multiple virus strains.  It is an internationally reportable disease to the world organization for animal health (OIE).​

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​Rabbit hemorrhagic disease is caused by rabbit hemorrhagic disease virus (RHDV), a member of the genus Lagovirus and family Caliciviridae. There are many strains of RHDV, and three major viral subtypes: RHDV (“classical RHDV”), the antigenic variant RHDVa, and the recently em​erged virus RHDV2 (also called RHDVb). Related lagoviruses, called rabbit caliciviruses, circulate in healthy rabbits. These viruses can confer varying degrees of cross-protection to RHDV.

​While most rabbit caliciviruses do not appear to cause any illness, two potentially pathogenic strains have been reported. One virus identified in the U.S. (proposed name “Michigan rabbit calicivirus”) was isolated from an outbreak that resembled rabbit hemorrhagic disease, although an attempt to reproduce the disease in experimentally infected rabbits resulted in little or no illness. A related strain, the Ashington strain of rabbit calicivirus, was recovered from dead wild rabbits during an outbreak in Europe.​

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​There are many strains of the RHD virus, but three are of most concern. RHD Type 1 has two forms, RHDV and RHDVa. RHD Type 2 has just one form, RHDV2. The two forms of Type 1 are quite similar and their vaccines are cross-protective. They tend to not affect young bunnies but have a very high mortality rate for adult rabbits. RHDV2, on the other hand, seems less deadly than the Type 1 strains, but affects all ages of rabbits. The RHDV2 vaccine only protects against that type. All RHD virus types are in the viral family Caliciviridae and genus Lagovirus.​

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​Only laboratory tests can confirm a diagnosis of RHD. However, RHD should be suspected if a rabbitry experiences illness in most/all rabbits, high fevers, poor appetites, depression, inactivity, bloody discharges, seizures, and/or sudden death. Call your veterinarian right away if you have any concerns about your rabbit's health. Usually RHDV2 is associated with mass morbidity (illness) and mortality (death) in a colony or herd.​

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​Rabbit hemorrhagic disease spreads between rabbits mostly by ingestion and inhalation of the virus. The virus is present in urine and feces from infected rabbits, so contaminated bedding, food or forage can be a source of infection. The virus can be moved from place to place mechanical vectors and fomites (flies, predators, scavengers, feral domestic and wild rabbits, vehicle tires, clothing, footwear, cages, equipment, and wind and water movement).​

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​RHD is not a zoonotic disease and there is no public health significance. RHD is specific to rabbits. Dogs, cats, and other pets cannot contract the disease, but can transport the virus just like vehicles, shoes, and equipment can.​

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​Exposure to the virus does not necessarily mean a rabbit is infected with the virus. Some rabbits will just be exposed; others will be exposed and become infected and either die or recover. Recovering rabbits will develop antibodies to the virus and become resistant to related calicivirus strains for an unknown period. Infected rabbits can “carry" or shed the virus for over a month, perhaps up to four months (when experimentally infected); they are not believed to be infected and shed for life.​

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​The RHD virus was first identified in China in the early 1980s.  Outbreaks occur periodically throughout the world and continually in some countries but have been quite rare in North America. Since 2019 RHDV2 has been an emerging disease issue in North America; British Columbia experienced outbreaks of RHDV2 in 2018-2019, primarily on Vancouver Island. Isolated cases were reported in OH in 2018 and NY in 2020. WA had an outbreak in 2019-2020. A multistate outbreak in NM, AZ, CA, CO, TX, NV and UT started in 2020 and is ongoing. Mexico has also confirmed detection of RHDV2 virus in 6 northern states. The source of the recent RHDV2 outbreaks has not been identified.​

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The RHDV2 viruses in the North American outbreak are phylogenetically different. The NVSL Foreign Animal Disease Diagnostic Laboratory completed full genome sequencing and analysis of rabbit hemorrhagic disease virus 2 (RHDV2) isolates detected in the United States from 2018 through 2020, including from the ongoing outbreak in the southwestern United States.

The phylogenetic analysis indicates isolates cluster by geographical region (NY, OH, and WA are all different from SW states). The most recent southwestern isolates form a single genetic cluster suggesting that the outbreak of RHD in these states was caused by the introduction of a single genetic isolate into the region; this virus is responsible for the disease in both wild rabbits and hares and domestic rabbits.​

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​The virus can survive for long periods outside the host. Environmental temperature, humidity, and protection by organic material are important factors in virus survival. Viable virus has been detected for as long as 105 days on a fomite at room temperature and in decaying tissue of infected carcasses for up to 90 days; it persists in chilled or frozen rabbit meat. The virus can remain viable for 22-35 days at 72°F. It survives freeze-thaw cycles. Pelts from dead wild or domestic rabbits in premises or geographic areas during an RHDV outbreak should not be processed, transported or sold.​

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