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Rabbit Hemorrhagic Disease

Rabbit hemorrhagic disease (RHD) is caused by a calicivirus. Currently, the rabbit hemorrhagic disease virus serotype 2 (RHDV2) viral strain is mostly of concern in the Western United States and Canada. The reported mortality rates for rabbitries, domestic or wild populations is between 5%-80%, and could be more. 

Previously, RHD virus serotype 1 (RHDV1 or RHDVa) strain was of serious concern because its mortality rates were between 40-100%. However, the RHDV1 strain is not spreading as fast as it once did. 

Beyond the high mortality rates with both strains, the other frightening aspects with this virus are:

#1. The RHDV2 viral strain affects more rabbit species than the RHDV1 viral strain. 

#2. There is little or no cross-protection between the two strains. 

#3. Their persistence and the variety of ways they can spread within the environment. 

#4. The impact on the ecosystem. 

We will cover each of these aspects, but first let’s discuss the symptoms. 

Symptoms

While most of the research has focused on RHDV1 because it has been around longer, the symptoms between the two strains are similar.

Oftentimes, the only signs of RHD are sudden death and blood-stained noses caused by internal bleeding. These infected rabbits die suddenly due to inflammation of the liver (hepatitis), which prevents or impairs synthesis of several blood clotting factors. 

If a rabbit does exhibit signs, these include:

  • Bleeding from nose, mouth or other body parts 
  • Breathing difficulties
  • Fever
  • Inappetence (lack of hunger)
  • Jaundice
  • Lethargy
  • Spasms or seizures
  • Vocalizations

Affected Rabbit Species

RHDV1 has only affected domestic rabbits or wild European rabbits. These are the companion pet rabbits that many people have.

RHDV2 affects those rabbits, but also jackrabbits, hares, and wild American cottontails. Other rabbits and pikas may also be susceptible.

At this time, people and other animals are not affected by these strains. However, different strains of caliciviruses are found in other mammals, and is especially common in cats. 

Little or No Cross-Protection

As we had stated earlier, there is little or no cross-protection between RHDV1 and RHDV2. You might find that confusing since they cause similar symptoms. But then, poor or little cross-protection also occurs with several of the recently identified clinical strains (serovars) of leptospirosis. 

Transmission

RHDV1 and RHDV2 remind us of parvovirus in dogs due to their hardy and persistent nature. Canine parvovirus can survive up to one month indoors and can live for several years outdoors depending on the environmental conditions. The primary source of the canine parvovirus virus is from the feces of infected dogs that can be either ingested or inhaled, as well as be spread via direct contact, or even via clothing or shoes. 

Indeed, rabbits may inhale or ingest the RHD virus with direct or indirect contact with other infected rabbits. Both RHDV1 and RHDV2 viral strains are very resistant to extreme heat or cold temperatures, and can persist in the environment up to three or four months. The virus is present in urine, feces and respiratory secretions. Predators can spread the virus by moving infected rabbit carcasses. Contaminated bedding, clothing, and shoes can all be indirect sources of infection. Transmission can also occur through contaminated food and water. Infected insects, rodents, birds or other animals that can serve as vectors and pass the virus to more rabbits. 

Also similar to canine parvovirus, bleach can inactivate the virus and companion rabbit caregivers will need to be extra vigilant at decontamination as well as in following biosecurity measures. The U.S. Department of Agriculture (USDA) provides a document called the General Guidance for Cleaning and Disinfection or Rabbit Hemorrhagic Disease Virus (RHDV) Contaminated Premises. The California Department of Food and Agriculture (CDFA) gives additional tips

Environmental Impact

You may be wondering why the USDA and CDFA are the leading agencies here instead of fish and wildlife departments. The primary mission of these agencies is to safely secure the food chain supply for people and animals. However, the U.S. rabbit industry has a very large economic impact as it is estimated to be worth around $2.3 billion of which 80-90% percent makes up the value of pet supplies and care of over 6.7 million pet rabbits. 

As more background, the outbreak of RHDV2 was first identified in 2010 in France. After the virus ravaged the wild rabbit population in the Mediterranean region of Europe, there was a direct correlation with the population decline of their main predators. The Iberian lynx population declined by 65% population, whereas the Spanish imperial eagle declined by 45%. 

In North America. If RHDV2 becomes rampant and kills 80% of the rabbit population, coyotes could start hunting domestic livestock, which endangers the global food chain.

From an environmental perspective, ranchers then might start removing the coyotes and if poisoned, their carcasses could kill important scavengers like eagles and vultures. It took the U.S. approximately 40 years to regenerate the bald eagle population. 

Rabbits also play an important environmental role besides being a source of food. They help disperse seeds and provide weed control through grazing. Indeed, rabbit droppings increase soil fertility and plant growth, alter plant species composition and vegetation structure through grazing and seed dispersal, This creates open areas and preserves plant species diversity. 

Vaccine

At this time, the European Union (EU) has three licensed vaccines against RHDV2, while no vaccines are licensed to date in the U.S. 

However, two of the three EU vaccines are being allowed for emergency use in the states with confirmed cases of RHDV2. 

If you have a companion pet rabbit and live in one of these states, please contact your veterinarian who can seek approval to administer the vaccine or apply for its importation from the state veterinarian. 

What to Do

If you have a companion pet rabbit, you need to follow the biosecurity measures outlined by the USDA or contact your veterinarian about next steps.

If you see a sick or dead rabbit in the wild or along trails, you need to contact your state’s wildlife officials. DO NOT TOUCH OR HANDLE and KEEP YOUR PETS AWAY FROM THEM. The rabbit could have died from another reason or infectious diseases such as the bubonic plague or tularemia (rabbit fever). Both of those diseases are highly contagious, are considered bioweapons, and are easily transmissible to humans and other animals.  

References

Delibes-Mateos, Miguel et al. “Key role of European rabbits in the conservation of the Western Mediterranean basin hotspot.” Conservation Biology: the Journal of the Society for Conservation Biology vol. 22,5 (2008): 1106-17, doi:10.1111/j.1523-1739.2008.00993.x, https://conbio.onlinelibrary.wiley.com/doi/10.1111/j.1523-1739.2008.00993.x

“Rabbit Hemorrhagic Disease (RHD).” Animal Health and Food Safety Services Division – Animal Health Branch, California Department of Food and Agriculture, 20 Aug. 2021, https://www.cdfa.ca.gov/AHFSS/Animal_Health/RHD.html

“Risk Identification.” USDA Animal and Plant Health Inspection Service, USDA, 8 Feb. 2021, https://www.aphis.usda.gov/aphis/ourfocus/animalhealth/SA-Epidemiology-AnimalHealth-CEAH/Risk+Identification

Stokstad, Erik, “A Deadly Virus Is Killing Wild Rabbits in North America.” ScienceInsider, Science, 20 May 2020, https://www.science.org/news/2020/05/deadly-virus-killing-wild-rabbits-north-america.

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