The Shadow of RHDV2: Experts Warn of Ongoing Threats and Inevitable Mutations in Rabbit Hemorrhagic Disease

By Our Think Tank
Published by the House Rabbit Society

Main Facts

Rabbit Hemorrhagic Disease Virus 2 (RHDV2), a highly contagious and frequently fatal calicivirus affecting both domestic and wild lagomorphs, remains one of the most significant biological threats to rabbit populations worldwide. In a recent episode of Medgene’s podcast, Every Animal Has an Owner, veterinary experts Dr. Amanda Jones and Dr. Anthony Pilny delivered a sobering analysis of the virus.

Their discussion moved beyond basic biosecurity, offering a comprehensive look at how RHDV2 devastates rabbit physiology, how veterinary pathologists conduct forensic assessments of outbreaks, and what the future holds as the virus continues to adapt. According to the experts, the primary danger of RHDV2 lies not only in its extreme virulence and environmental persistence but also in its capacity for genetic mutation. As the virus circulates through wild and domestic populations, the likelihood of novel strains emerging increases, posing a continuous challenge to vaccine efficacy and veterinary medicine.

The conversation highlights a critical reality for rabbit owners, shelter operators, and wildlife officials: RHDV2 is not a localized crisis of the past, but an enduring epidemiological challenge requiring constant vigilance, advanced diagnostics, and proactive immunization strategies.

Chronology: The Emergence and Spread of RHDV2

To understand the gravity of the warnings issued by Dr. Jones and Dr. Pilny, it is necessary to examine the timeline of how RHDV2 established itself as a global menace.

• 2010 (The Discovery): RHDV2 first emerged in the Iberian Peninsula (France and the surrounding region), diverging from classic strains of Rabbit Hemorrhagic Disease Virus (RHDV1). Unlike classic RHDV—which historically targeted only adult European rabbits (Oryctolagus cuniculus)—RHDV2 demonstrated a wider host range, affecting younger rabbits and various other species within the leporid family.
• 2013–2018 (Global Expansion): The virus rapidly transcended European borders, making its way across the globe through international trade, fomites (contaminated clothing, shoes, and equipment), and movement of wild populations. It established footholds in Australia, New Zealand, and various parts of the European continent, devastating wild rabbit populations and causing catastrophic losses in commercial rabbitries.
• 2020 (The North American Incursion): RHDV2 made a significant and devastating leap into North America, with major outbreaks recorded in the southwestern United States (particularly New Mexico, Arizona, and Texas). The virus swept quickly through wild jackrabbit and cottontail populations, as well as domestic rabbit communities, catching North American veterinarians and pet owners largely unequipped for the aggressive pathogen.
• 2021–2023 (Regulatory Approvals and Emergency Responses): In response to the North American crisis, regulatory bodies such as the USDA granted emergency-use authorizations (and later full conditional licenses) for vaccines like the Medgene RHDV2 vaccine. Rabbit owners and rescues mobilized nationwide to implement strict biosecurity protocols and vaccine campaigns.
• Present Day (The Mutation Era): As discussed on Every Animal Has an Owner, the current phase of the RHDV2 timeline is defined by endemicity and evolution. The virus is no longer viewed merely as an "outbreak" disease, but as a permanent fixture of the environment, forcing veterinary medicine to anticipate and track inevitable genetic mutations.

Supporting Data: Understanding the Virulence of RHDV2

The data surrounding RHDV2 underscores why veterinary professionals view the virus with such high levels of concern.

• Mortality Rates: RHDV2 boasts an alarmingly high mortality rate, often ranging between 70% and 90% in unvaccinated populations. In many cases, death occurs so rapidly that owners observe no clinical signs beforehand.
• Environmental Stability: The calicivirus is exceptionally hardy. It can survive extreme temperatures (both freezing and high heat) and remains viable on surfaces, in soil, and on organic matter for months. Standard household disinfectants are largely ineffective against it; veterinarians must rely on specific agents, such as accelerated hydrogen peroxide or targeted dilutions of household bleach, to properly sanitize environments.
• Host Range: Unlike traditional caliviruses that are highly species-specific, RHDV2 affects multiple species within the order Lagomorpha. This includes European rabbits, various North American cottontail species, and jackrabbits, creating a vast and difficult-to-control wildlife reservoir.
• Incubation Period: The incubation period is remarkably short, typically spanning just 1 to 5 days. Once infected, the virus targets internal organs—primarily the liver and spleen—causing rapid necrosis, internal hemorrhaging, and death, often triggered by disseminated intravascular coagulation (DIC).

Official Responses: Veterinary Forensics and Public Health Strategy

During their appearance on Every Animal Has an Owner, Dr. Jones and Dr. Pilny detailed the meticulous work required when an outbreak is suspected. Veterinary forensics plays a vital role in tracking RHDV2, as clinical signs can easily be mistaken for other acute systemic illnesses.

The Forensic Approach

When a sudden rabbit mortality event occurs, forensic investigation requires more than a simple visual examination. Veterinary pathologists must:

1. Secure the Scene and Specimen: Prevent the spread of fomites by properly bagging and handling deceased animals and examining the housing environment for potential vectors (insects, rodents, or human contact).
2. Histopathological Analysis: Examine liver, spleen, and lung tissues for characteristic lesions, necrosis, and cellular destruction.
3. Molecular Testing: Utilize Reverse Transcription-Polymerase Chain Reaction (RT-PCR) assays to confirm the presence of viral RNA, differentiating RHDV2 from classic RHDV and other hemorrhagic conditions.

Preventive Measures and Vaccination

Official responses from agricultural departments, state veterinarians, and exotic animal medical associations universally emphasize vaccination as the single most effective line of defense.

Dr. Jones and Dr. Pilny emphasized that waiting for an outbreak to occur before seeking vaccination is a failing strategy. Because the vaccine requires time to stimulate an adequate immune response—and because boosters are necessary to maintain immunity—proactive veterinary care is essential. Furthermore, strict biosecurity must be maintained even for vaccinated rabbits. This includes changing clothes after handling unknown rabbits, keeping indoor rabbits away from outdoor vectors, and carefully washing fresh greens sourced from areas where wild rabbits roam.

Implications: Preparing for Inevitable Mutations

The most critical takeaway from the expert discussion on Every Animal Has an Owner is the forward-looking warning regarding viral mutation.

RNA viruses like caliciviruses are notorious for high mutation rates due to the lack of proofreading mechanisms during replication. As RHDV2 continues to circulate through vast populations of domestic and wild rabbits globally, selective pressures are driving the evolution of new genetic variants.

What Viral Evolution Means for the Future

1. Vaccine Adaptability: As the virus mutates, pharmaceutical developers and immunologists must continuously monitor genetic drift. Vaccines that offer robust protection against current strains may need periodic updates to ensure cross-protection against emerging variants.
2. Shifts in Pathogenicity and Host Range: Mutations could potentially alter the severity of the disease or expand its host range further, increasing the risk to endangered or vulnerable wild lagomorph species. This presents a complex challenge for wildlife conservationists who have few tools available to vaccinate wild populations on a large scale.
3. The Need for Global Surveillance: Genomic surveillance must become a standard component of veterinary public health. Tracking the genetic lineage of RHDV2 isolates across different continents allows researchers to spot mutations early, alerting vaccine manufacturers and veterinary practitioners before a mutated strain triggers a new wave of catastrophic losses.

A Call to Action for the Rabbit Community

The insights provided by Dr. Amanda Jones and Dr. Anthony Pilny serve as both a warning and a roadmap. While the threat of RHDV2 and its future mutations is significant, the veterinary community is not powerless.

For pet owners, shelter directors, and wildlife advocates, complacency is the greatest risk. By embracing proactive vaccination protocols, maintaining rigorous biosecurity standards, and supporting ongoing scientific research and viral surveillance, the rabbit community can better shield vulnerable populations against the ever-changing landscape of RHDV2.