What's this crazy rabbit Ebola everyone is talking about?

First things first, there is no rabbit Ebola. This term is batted about due to the severity of symptoms of Rabbit Hemorrhagic Disease Virus (RHDV).

RHDV is a highly contagious calicivirus of rabbits. RHDV was first found in China in a major outbreak in 1984. However, it is suspected to have emerged in the late 1970s in Europe. In 2010, a new serotype was identified in Europe, named RHDV serotype 2 (RHDV2). RHDV2 has since become the dominant strain in many locations. RHDV (classic) and RHDV2 are considered endemic in Europe, Australia, New Zealand, some parts of Asia, and some parts of Africa. (Fun Fact: Australia introduced the virus to control the invasive rabbit population!).

RHDV1 is a virus of only the Oryctolagus genus, which includes domestic rabbits. RHDV2 can affect the genera Oryctolagus (domestic and wild rabbits), Lepus (jackrabbits and hares), and Sylvilagus(cottontails). RHDV2 is suspected to also affect pikas (Family Ochonotidae). There are a few other caliciviruses in rabbits including the European Brown Hare Syndrome Virus, but we will not discuss them further.

There have been multiple small outbreaks of RHDV2 in the United States. These infections were localized to small, isolated locations. In 2018, a small outbreak in southwestern Canada spread to domestic and feral rabbits in New York, Ohio, and Washington (primarily Washington). It is essential to recognize that this outbreak only stayed in domestic/feral rabbits. In late March 2020, RHDV2 was detected in a domestic rabbit. This outbreak quickly got into the wild rabbit species and spread throughout the southwest US and Mexico within only a few months (Figure 1).

Figure 1. 2020-2024 Rabbit Hemorrhagic Disease Map from the USDA-Aphis up to date on March 29, 2023.

You said people call it rabbit Ebola due to the clinical signs. What are the clinical signs?

RHDV causes severe hepatic necrosis resulting in disseminated intravascular coagulation (DIC). There are three forms of RHDV (4 in RHDV classic): Peracute, Acute, and Subacute to Chronic (RHDV classic also has asymptomatic).

Peracute

• Sudden Death (Most common sign)
• Terminal Signs (e.g., terminal vocalization, seizure, agonal breathing, etc.)

Acute (12-hour period)

• Lethargy
• Anorexia
• Low-grade fever
• +/- Bloody discharge from nose or genitourinary tract (Figure 2)
• +/- Neurological signs
• Incoordination
• Lameness
• Tremors
• Paddling
• Seizures
• End-stage: tachypnea, cyanosis

Subacute to Chronic (up to 2 weeks)

• Similar to acute, but signs milder and slower onset
• Jaundice can be present because there is time for this clinical sign to develop.
• Weight loss can be present because there is time for this clinical sign to develop.

Asymptomatic

• Occurs most often in rabbits infected with RHDV classic when younger than eight weeks old.
• +/- mild bloody discharge from nose

Figure 2. Rabbit presenting with significant hemorrhagic discharge. Photo credit: Marc Silpa March 2020.

Sounds horrendous! What's the prognosis?

Poor to grave if clinical signs are present. There is a large mortality range for both RHDV classic and RHDV2. RHDV had a reported range of 30-100%, with those younger than four weeks of age rarely dying. In the lab, experimentally infected rabbits with RHDV2 have a 20-30% mortality rate. However, naturally infected rabbits range from 5-100%, with the current US outbreak hovering around 60% mortality.

Oh, that sounds bad. But at least it's not very contagious… is it?

I hate to burst your bubble, but it is. RHDV(2) is spread through contact with virus particles through the oral, nasal, or mucous membrane route. While the oral route is the most common method of acquiring the virus, conjunctival infections only need a few live virus particles. Virus particles are found in all excretions and secretions of infected rabbits. Surviving rabbits have been found to have virus particles present 15 weeks after infection. In addition, the virus can survive long periods in a carcass or even just the fur (up to 7.5 months if the temps are low enough and 30 days at 70 degrees). The virus alone can persist in the environment for weeks. Worst of all, this virus readily spreads via fomites and mechanical vectors. For example, the virus can persist in flies for up to 9 days and be spread via the conjunctival route. And lastly, bird and mammal predators can excrete virus particles in their feces if they consume an infected rabbit or carcass.

You said fomites spread RHDV. Can I disinfect it?

Yes! The virus is inactivated with 4-10% sodium hydroxide, 1-2% formalin, and 0.5% sodium hypochlorite (household bleach). Other disinfectants that are effective against other caliciviruses should also be effective against RHDV but review the product information from the manufacturer.

This sounds like a horrible virus for poor Fluffy! Is there anything I can do to protect rabbits?

Yes. Depending on your country, there are approved vaccines for RHDV (both classic and type 2). In the US, MedGene has received emergency use authorization from the USDA. This vaccine requires a 21-day booster in naive animals. The available vaccines, including the new Medgene, prevent the disease effectively.

Oh No! Fluffy seems to have caught the virus. What can I do?

While no specific treatment is available, supportive care is the best chance of survival. Supportive care includes IV fluids, nutritional support (e.g., syringe feeding of Critical Care), and thermal support. However, strict isolation protocols should be maintained, given its contagiousness.

References:

Center for Food Security and Public Health. (2020, June 1). Viral Hemorrhagic Disease of Rabbits, Rabbit Calicivirus Disease, European Brown Hare Syndrome. https://www.cfsph.iastate.edu/Factsheets/pdfs/rabbit_hemorrhagic_disease.pdf

Oglesbee, B. L., & Lord, B. (2021). Gastrointestinal Diseases of Rabbits. In Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery (4th ed., pp. 186–199). Elsevier.

RHDV2 Risk identification. USDA APHIS | Risk Identification. (2022, November 15). https://www.aphis.usda.gov/aphis/ourfocus/animalhealth/SA-Epidemiology-AnimalHealth-CEAH/Risk+Identification

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About the Guide: Marc Andrew Charles Silpa, BVM&S

Dr. Marc Silpa is a Fear-Free certified veterinarian passionate about exotic animal care. With a BVM&S degree from the University of Edinburgh and additional training in zoo and aquarium studies, he has provided advanced veterinary care to a wide range of animals, from manatees and sea turtles to domestic pets and exotic animal species. Marc used to work as a marine mammal vet before moving to the desert. He was then hired at a mixed animal practice as the practice's exotic veterinarian. Currently, Marc works in a 100% exotic animal practice while pursuing board certification through ABVP (ECM).