Written By: Emilia Wong Gordon, DVM, DABVP (Shelter Medicine Practice)
Rabbit hemorrhagic disease (RHD) should now be on the radar of every shelter veterinarian in North America. This disease is caused by Rabbit Hemorrhagic Disease Virus 2 (RHDV2), a hardy calicivirus that resists freezing and many household disinfectants. Mortality rates in North American rabbit populations are very high- in some cases as high as 100%. While we have had RHDV2 in BC since 2018, a newer strain (AZ1) first identified in the Southwestern US is now spreading across North America. In the last few months, there have been confirmed cases in AB and ON. Because this strain can infect wild rabbits, it is expected to become endemic and pose an ongoing threat.
Clinical signs
The incubation period of RHDV2 is 1-9 days, and clinical signs are variable with sudden death as the most frequently reported clinical sign in several BC outbreaks (based in a private home, a shelter, and a sanctuary). Other clinical signs include inappetence, seizures, jaundice, epistaxis, and dyspnea.
Shelter veterinarians and other shelter team members as well as field officers should be on the alert for possible cases in the field or in incoming or recently admitted rabbits. Red flags that increase the suspicion of RHD include:
- Death of multiple wild or domestic rabbits within days, in the same area, household or facility
- Deceased rabbits are in good body condition
- There is no other obvious cause of death (e.g. trauma); there may or may not be visible blood at orifices
Diagnostics
The most useful diagnostic tool is PCR on samples collected at necropsy. All suspicious cases should be necropsied and tested unless they are deemed ineligible for testing. Practitioners are strongly encouraged to submit whole carcasses if accepted by a provincial, federal, or academic lab in the area; often this type of testing will be done at no charge. Frozen carcasses are typically acceptable.
If doing a necropsy yourself, the following tips may be helpful:
- Check with your preferred lab prior to necropsy to ask about sample selection and storage for RHD testing. Typically, samples of multiple organs listed below will be requested and should be submitted frozen (do not place in formalin for PCR testing).
- Wear full PPE
- Assess the carcass carefully for another cause of death, in particular trauma that may not have been evident without close examination
- Gross findings are variable and range from no visible abnormalities to gross hemorrhage affecting multiple organs and body cavities. If the gross necropsy is unremarkable but no other cause of death is found, RHD cannot be ruled out and organ sampling for histo and PCR should be performed.
- At minimum, lung, liver, and spleen should be sampled (plus any other organs that appear abnormal or are requested by the specific lab). These samples can be pooled for PCR.
- Histopathology will often reveal microscopic hemorrhage in organs such as the lungs, liver, heart, spleen, and kidneys.
Several academic and provincial labs in Canada offer RHDV PCR, and eligible samples can be forwarded to a federal laboratory for sequencing if indicated. RHD is a federally notifiable disease, and in many provinces (including ON) it should also be reported to provincial animal health authorities.
Prevention
As there is no approved treatment for RHD and most affected animals will die, shelters should focus on prevention. The time to do this is NOW. There are several resources available for shelter and sanctuary operations, including a regularly updated BC SPCA Information Sheet for Shelters, Rescues and Sanctuaries.
The cornerstones of prevention for shelters are:
- Minimize the number of rabbits in care at any given time
- Vaccinate all rabbits in shelter and foster care; vaccinate new rabbits right at intake
- If in or near an affected area, quarantine incoming rabbits for 10-14 days with PPE changed between primary enclosures. If healthy, these rabbits can still be available for pathways such as foster or adoption but precautions such as spatial segregation and PPE should still be used. This is especially important if the resident shelter rabbit population is not vaccinated.
- Follow standard infection control measures such as observing an order of care from lowest to highest risk, using robust biosecurity between rabbits, using a disinfectant effective against non-enveloped viruses, etc.
- Strict exclusion of wild and feral rabbits from accessing food, supplies, and areas where shelter rabbits are housed
Vaccine information
There are three RHD vaccines currently in use in North America, with the two European products (Filavac VHD C + V and Eravac) most commonly used in Canada. These are preferred over the American product (Medgene) for shelter use, because they have an onset of immunity of 7 days vs 35 days for the Medgene product.
Over 16,000 doses of the Filavac product have been given in BC, and it is now readily available in Canada through Ceva Animal Health and stocked by major purchasing groups. This product comes in blister packs of 10 single-dose vials and can be given as a single dose to rabbits over 10 weeks of age and repeated in 6-12 months. The cost is $20-25 per vaccine, so it is relatively expensive.
Shelters have expressed concerns about cost, but are strongly encouraged to think beyond these short-term concerns and proceed with vaccination for the following reasons:
- Most shelters take in a relatively small number of rabbits each year compared to other companion animal species, but rabbits also tend to have a very long length of stay compared to other species
- This means that many shelters are have multiple rabbits in their system at any given time
- An RHDV2 incursion into a shelter with multiple unvaccinated resident rabbits has a strong likelihood of resulting in mass mortality through spontaneous death or depopulation
- This poses a health risk to domestic and wild rabbits in the community, if the disease is not contained in the shelter. There is also a large reputational risk associated with mass mortality events.
- The public and rabbit owners expect shelters to take all measures possible to prevent cases of this disease; vaccinated rabbits may also hold extra appeal to adopters
- The vaccine is extremely safe and each rabbit will most likely only need one vaccine during a shelter stay; it should not need to be repeated unless LOS is excessively long
Shelters in provinces where they are allowed to offer veterinary care to the public may also be interested in offering vaccine clinics, particularly to guardians who don’t have a regular veterinarian or are unable to access care for financial reasons. The most cost-effective way to do this is with a multidose vial of Filavac, which typically yields 40-45 vaccine doses and costs under $200. This product must be used within 2 hours of opening and may not be accessible through all purchasing groups; practitioners who cannot order it locally may be able to access it through the CCVB application process. Clients should receive an information sheet about the vaccine including risks and regulatory status.
Conclusion
Shelters, rescues, and sanctuaries- and the veterinary teams working with them- have a key role to play in RHD surveillance, response, prevention, and education. Thankfully, combining what we know about RHDV2 with foundational infectious disease control concepts enables us to make our best contributions in these areas! These efforts mean a lot to rabbits and bunny lovers in our communities- they are worth it.
Watch the Webinar Recording – Exclusive to OMSA Members. (If you’re interested in becoming a member, please see here.)
Watch the September 2022 webinar with Dr. Wong Gordon, DVM, DABVP (Shelter Medicine Practice) here.
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