Rabbit Hemorrhagic Disease

This fact sheet was updated August 2020. 

Other names: rabbit viral hemorrhagic disease, rabbit viral sudden death, X-Disease of Rabbits, hemorrhagic septicemia syndrome in rabbits, hemorrhagic tracheitis of rabbit, viral hemorrhagic pneumonia in rabbits, rabbit plague.

Cause

Rabbit hemorrhagic disease virus (RHDV) is a highly contagious and deadly calicivirus that affects some species in the larger group (Order) of Lagomorphs, which includes all rabbits, hares and pikas. RHDV1 was first discovered in 1984 in China and has since spread around the world causing hundreds of millions of domestic rabbit fatalities. All caliciviruses are capable of frequent mutation, and consequently, there are multiple strains or serotypes of RHDV. The other more recent serotype, RHDV2, emerged in Europe in 2010 and was confirmed in wild hares and rabbits for the first time in the United States in 2020. 

Significance

Because mortality can reach 70% or higher RHDV can cause dramatic declines in wild rabbit populations, especially when first introduced. In Spain’s Iberian Peninsula, steep rabbit population declines negatively impacted ecosystems by dramatically reducing a source of food for predators, including the endangered Iberian lynx. As a result of its high fatality rate, RHDV1 has been used as biocontrol for wild non-native rabbits in Australia. In early 2020, RDHV2 was confirmed in the United States in not only domestic rabbits but also in wild cottontails and jackrabbits. Now there is also concern for the New England Cottontail, a species still recovering from population declines.

Species Affected

Only members of the rabbit family (Lagomorphs) are susceptible including all domestic, feral, and wild rabbits and hares. RHDV is not a zoonotic disease affecting humans. 

Distribution

RHDV1 has been confirmed in 40 countries across Europe, the Mediterranean, Africa, Asia, North America, as well as Australia and New Zealand. Because the domestic European rabbit is the main reservoir host and does not occur in the wild in the US, RHDV1 is not thought to be established (enzootic) here. However, sporadic RHDV1 outbreaks have appeared intermittently among domesticated rabbits. For example, cases were confirmed in Iowa in 2000; Utah, Illinois, and New York in 2001; Indiana in 2005; Maryland in 2008; Minnesota in 2010; and Pennsylvania in 2018.

The RHDV2 strain appears to have emerged in France in 2010, and spread rapidly across Europe and the Mediterranean. It was detected in Australia in 2015. In 2018, RHDV2 was first detected in feral rabbits in British Columbia. A few months later it was confirmed in a pet rabbit in Ohio as well as pet and feral rabbits in Washington. In early 2020, RHDV2 was identified as the cause of death in both domestic and wild rabbit species in Texas, New Mexico, Arizona, Nevada, Colorado, and most recently, in California.

Transmission

Rabbits infected with RHDV can spread the virus for up to a month in their urine, feces, blood, and secretions. The virus can then infect other rabbits through oral, nasal, or conjunctival routes. The incubation period for RHDV ranges from 16 to 48 hours, and fatalities usually occur 2 to 3 days after infection.

Spread of RHDV can occur through direct contact, exposure to infected carcasses or animal products, rabbit fur, food, water or clothing, and mechanical vectors such as insects, scavengers and predators.

RHDV2 is very resistant to environmental degradation and can survive long periods outside the host. It has survived at room temperature for as long as 105 days, it can survive freezing, as well as heat of 122F for one hour, and it has been detected in decaying tissue after 90 days outdoors.

Clinical Signs

The clinical signs of disease do not differ between the various viral strains of rabbit hemorrhagic disease but there are four main clinical forms of RHDV infection; in the very rapid peracute disease, clinical signs are usually absent except terminal vocalizations, followed by collapse and death within 12 to 36 hours.

The less rapid acute form may present with a wide range of signs such as bleeding from the mouth, nose or rectum, fever, difficulty breathing, neurological signs such as loss of coordination and seizures, depression, lethargy, and loss of appetite. Hemorrhages in the eye, blood in the feces, and yellow mucus membranes may also be observed secondary to anemia and coagulation abnormalities caused by the virus.

The subacute form is characterized by the same clinical signs but they are less severe.

Lastly, the chronic or subclinical form of the infection can affect a small percentage of animals. These cases are usually lethargic, jaundiced, and in poor body condition and may still die. Survivors of either this or the subacute form are then protected with apparently life-long immunity.

Diagnosis

RHDV is diagnosed through necropsy and molecular tests. On necropsy, the most common lesions are a pale liver and an enlarged spleen. Hemorrhages in other locations like the trachea, lungs, heart, liver, spleen, and kidney can also be observed. 

Treatment

There is no treatment available for rabbit hemorrhagic disease apart from supportive care. In the wild, rabbits are often found dead. 

Management

RHDV is a foreign animal disease (not currently established in the US) so if it is detected in the US, it must be immediately reported to state agricultural authorities who act for and coordinate with USDA. The Northeast Wildlife Disease Cooperative (NWDC), the USGS National Wildlife Health Center, and others are alerting partners to be vigilant for morbidity or mortality events involving wild rabbits. NWDC will facilitate submission of rabbits and hares suspected of this disease to the National Wildlife Health Center. Outbreaks of RHDV in the past (in domestic rabbits) have been managed through quarantine, depopulation, disease tracing, along with cleaning and disinfection. Though a vaccine for RHDV2 exists, it is not currently available in the US. Furthermore, eradication of RHDV2 is not likely to be possible once the virus is established in wild hare or rabbit populations due to the ease of transmission and long persistence of the virus in the environment. Therefore, vigilance and strict biosecurity measures are key to preventing RHDV2 from becoming established in wild populations. These Best Management Practices for the different groups such as zoos and rehabilitators who might encounter suspects are being developed and will be distributed to states.

Wildlife professionals, hunters or individuals who handle rabbits in the field should wear personal protective equipment (PPE) and decontaminate all field gear, clothes, and vehicles in order to prevent the spread of RHDV2 in populations of wild rabbits or transmission to domestic rabbits. Field necropsies of RHDV suspects are strongly discouraged and instead, it is recommended that the whole carcass be collected, double bagged, and refrigerated before notifying state agricultural authorities.

The following additional guidance is provided for rabbit hunters:

  • Do not harvest rabbits that appear sick.
  • Wear rubber or disposable nitrile gloves while handling and cleaning game.
  • When cleaning game, bag and dispose of remains in an approved fashion, including burying them deeply enough to prevent scavenging, or placing them in the commercial waste stream.
  • When done handling game, wash hands thoroughly with soap and water, then clean and disinfect knives, equipment, and surfaces that were in contact with game. A viricidal solution can be made form 1 part bleach to 9 parts water. Clothing should be immediately washed and thoroughly dried.
  • All game should be thoroughly cooked to an internal temperature of 165F degrees.

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