Down the Rabbit Hole: The Status of RHDV2 in Ohio & Beyond
The highly contagious rabbit hemorrhagic disease virus type 2 (RHDV2) was first detected in the United States in 2018 in Medina County, Ohio. Since then, it has spread across the country, decimating both wild and domestic rabbit populations. In today’s episode, we sit down with two exotic companion mammal veterinarians to learn more about this deadly disease and the new vaccine to prevent it.
An avian and exotics veterinarian, Dr. Jew is passionate about educating pet owners on proper husbandry for exotic pets. He has a special interest in reptile medicine and surgery. Learn More »
Mia Cunningham: Thank you for tuning into the Fully Vetted podcast. My name is Mia Cunningham and along with my colleague Krysten Bennett, we’re joined today by Dr. Susan Borders and Dr. Nicolas Jew to learn more about rabbit hemorrhagic disease virus. Thank you both for being here with us today.
Nicholas Jew: No problem.
Susan Borders: Thanks for having me.
MC: Before we jump into today’s topic, we wanted to learn a little bit more about you both, if you could each share with us, just kind of like a snapshot of your professional backgrounds. Dr. Borders, we’ll start with you.
SB: Sure. So I graduated in 1998 from Ohio State and was a practice owner for many years at a small animal and exotic practice that Dr. Jew and I worked together closely for six or seven years. I currently am a full-time associate at the Animal Hospital of Pataskala, where I still perform small animal medicine and surgery with a special interest in exotic species, which is mostly the exotic companion mammals—a lot of bunnies. I also operate a mobile in-home wellness-only practice for exotic animals in my spare time.
MC: Nice. Thank you for sharing. Dr. Jew?
NJ: Yeah, so I graduated from Ohio State’s vet school in 2013. And I worked with Dr. Borders for seven years, cutting my teeth and learning about rabbits, because prior to that, I had never actually touched a rabbit in a veterinary situation before. Since then, I’ve moved into specialty exotic animal practice over at MedVet in Hilliard for coming up on two years now.
Krysten Bennett: As Mia said, we asked you on the show today to talk about rabbit hemorrhagic disease virus type two. Can you give us a quick overview of RHDV2? Where did it come from, and when did it first show up in the U.S.?
SB: Rabbit hemorrhagic disease virus originated in Europe. They first identified it in 1984 as RHDV1. It was responsible for decimating a large portion of the wild rabbit and hare population in Europe. Then they identified the RHDV2 variant and classified as a foreign animal disease; I believe it was first detected in France in 2010. In the United States, we had our first confirmed cases actually here in Ohio in 2018 with two confirmed cases in Medina. It sparked a large effort and investigation here in the United States since then.
MC: What are some of the clinical signs doctors should be aware of in suspected cases?
NJ: It can be really tough, because sometimes—especially if you’re operating a large-scale rabbitry—the symptoms are really vague. It could just be they’re lethargic, they’re not eating, maybe they seem a little to have a little malaise, and then all of a sudden you find them deceased with bloody hemorrhagic fluid coming from their orifices. And then a lot of times, they have this really classic posture where their back and neck are arched in a post-mortem situation, which is really sort of specific to this virus, as well as a few other things that happen to people. They can incubate this strain of the virus for up to two weeks before they show symptoms, but it can be incredibly vague. It can be one of those things where symptoms don’t show up until a few hours before they pass away.
MC: So because it’s so vague, do they administer testing for it?
NJ: There’s no antemortem testing that’s accurate. You have to submit histologic samples, and then they not only look at histology, but they also look at trying to isolate the virus as well as the antibodies against the virus with PCR as the confirmatory test. But there’s no antemortem testing that has reliability to it.
KB: Given that there’s no test available and the fact that RHDV2 is a highly contagious disease, slowing or preventing it from spreading is really important. Do we know how long the virus survives outside a host and how it is transmitted?
NJ: There’s a variety of ways that can be transmitted. You can have direct transmission from respiratory and oral secretions that can be passed in bodily fluids, so direct contact with rabbits that are infected. It can also be carried by people, so it can be on your clothes, it can be on your shoes, it can be on the food or grains that you bring it from outside. Insects can potentially carry the virus, and arthropod vectors are believed to be one of the main ways that this virus is transmitted. It can also be isolated out of dead tissue for up to three months after the an animal is passed away. So, if you have wild rabbits around your property and one of them dies and no one notices, you could potentially end up bringing that virus in, even if the rabbit has been deceased for an extended period of time.
SB: Also, they suspect that it can remain outside the host for up to three to four months. So there’s a concern that you don’t necessarily have to have contact with a deceased animal; you could just be inadvertently carrying this virus in on clothing or shoes. And that’s a huge concern, that we could be bringing it unknowingly, without ever suspecting, and putting our house rabbits at harm.
NJ: When the outbreak first started moving east from the West Coast, a lot of people got really concerned about hay as a potential fomite, because a lot of the hay that people buy commercially comes from the Pacific Northwest in the western states. Luckily, though, that hay is typically aged for several months in a well-contained bio-secure facility, so if you’re buying a reputable brand like Oxbow, it’s not a huge concern. But there were definitely people—especially folks that are cutting their own hay or baling their own hay—that thought that might be the way that their bunnies were getting infected.
SB: I do have some clients that are actually freezing their hay for a period of time, although RHDV2 is a very hardy virus. It can sustain a lot of various temperatures, ranging from 4 to 60 degrees Celsius, so we don’t know for sure that freezing kills the virus. It is very hardy in very cold conditions, and they’ve had outbreaks even in Canada in the middle of winter.
MC: How long do surviving animals remain contagious?
NJ: There are reports of chronic infections. Those chronic infections are really hard to diagnose because there’s no antemortem testing, and so chronic infections are probably something that’s really challenging to identify. And we don’t exactly have all the data to say how long those chronically infected rabbits shed the virus for and could they potentially be in your home shedding virus to your other rabbits. But the vast majority don’t survive.
SB: Some reports have suggested up to 30 days if they’d survive, but because we can’t identify the survivors, we just don’t know.
KB: As far as you can tell at this point, it’s pretty much fatal.
SB: Yes, there’s a very, very high mortality rate, upwards of 100% suspected with this strain of RHDV.
KB: And is that across the board for all species of rabbits, wild and domestic?
NJ: It seems to be.
SB: Yeah, so we’ve heard of it in the wild hare population, pikas, other Lagomorph-type species.
NJ: There was a report last year about some wild cottontails that only live in one part of the Grand Canyon that they were worried about extinction from the virus, which happened in Europe with the first RHDV.
SB: And there’s a small population of pygmy rabbits in Utah that they’re concerned about extinction. And this is a big reason why we’re trying to protect not only house rabbits, but obviously our wild rabbit population too, because it could really affect many ecosystems, if we see a decimation of our natural species here in North America.
MC: Is it transmittable to humans?
SB: Nor other species.
KB: I remember there being a lot of news coverage back in 2018 when RHDV was first found in Ohio, but now it seems like it’s tapered off quite a bit. What’s the status of the virus at this point? How far has it spread since then?
SB: On the most updated map that I just checked, there have been active cases all year, in the Pacific Northwest down through California and definitely in Texas, which seems to be a hotbed right now. But there were actually more positive cases of domestic rabbits in the states close to Ohio in the past year—Kentucky, Pennsylvania, I believe New Jersey, and Canada is a hotbed too for this. And so if you look at the map, it’ll make the distinction between wild and domestic rabbits, and there’s a very strong concern for both out west. But frankly, it seems like—maybe because we’re not identifying positives in the wild enough here—but the positives affecting our surrounding areas appear to be mostly domestic rabbits from what I’ve seen.
NJ: Yeah, everything that I’ve been reading has indicated that domestic rabbits seem to be the main reported cases in the Midwest. And you know, there’s no evidence to support this, but I sometimes worry, does that mean that we’re just not actually getting enough information out there to say like, “Hey, if you find a rabbit that’s deceased in the wild, you should probably be reporting that to the local wildlife official or the Department of Natural Resources,” versus do we potentially have a case where we’re developing a natural reservoir, and so those animals are no longer as clinically affected or their mortality rates are going lower? So I think it can be something where we have some interest in research in the future through the Department of Natural Resources or USDA.
MC: Can you talk to us about the biosecurity measures that should be taken in a clinic or in a rescue if they do find that they’ve had case?
NJ: The biggest thing is that you have to consider yourself as a potential fomite or vector, right? So you have to basically treat this like any other agricultural disease where you’re cleansing your shoes, you’re changing your clothes, you’re wearing gloves, maybe you’re even wearing disposable PPE that covers your clothing to make sure that you’re not bringing the virus out of a potential quarantine situation. You know, what’s great though, is that common disinfectants work really well; diluted bleach, accelerated hydroperoxides, the Virkon-style disinfectants are all effective at killing the virus, and the contact time needed is typically under 10 minutes. So as long as people are practicing good hygiene, wearing appropriate protective equipment, and disinfecting, it could be something that’s relatively easy to maintain. I think the harder area where biosecurity becomes challenging is where you have a large number of rabbits living in a situation where it’s hard to contain potential non-human vectors, or where you have a segment of the population where the bunnies are in contact with the public. Because I think in that circumstance, it’s hard to close your rescue to the public because you need those people coming in and out to adopt rabbits, to bring in donations, to make sure that you’re getting the word out about rabbits that need homes. But in an outdoor or a barn-style rabbitry situation, I’d say that your biosecurity is even more challenging, because the potential for insect vectors and other animals that are wild to bring the virus in or to spread it from within your quarantine zone is pretty high.
KB: With no antemortem testing available for such a hardy and contagious virus, what can rabbit owners and shelters do to prevent RHDV from getting in and infecting their animals?
SB: We’ve really encouraged rescue groups and private individuals that might be breeding rabbits or showing rabbits to quarantine any new rabbits for a good 10 to 14 days prior to introducing them to their facility if possible. Obviously, that’s challenging to do for our rescue groups. We do have a very large population of house rabbit rescues here in central Ohio and across Ohio. That’s sometimes challenging, but we can still encourage them to try to keep them separated as much as possible.
KB: You’ve talked a lot about how tough this virus is and how it can survive a pretty wide range of conditions. So, given that, in the event of an outbreak, are there any extra considerations for an owner or shelter when they’re disposing of potentially contaminated materials, you know, beyond what they normally do for any other outbreak?
SB: Anything that has active virus on it, you want to clean as much as possible to get as much infected debris off, and then dispose of that no different than you would any other infectious waste. The more you can disinfect it prior to disposal the better. Again, that contact time with a diluted bleach solution or one of the other products that Dr. Jew recommended would be important.
MC: Dr. Jew, you touched on this a little bit, but could you go into a little further detail for me about how doctors or clinics should report cases?
NJ: Your first step is contact the office for the state veterinarian and then contact your local USDA official. Oftentimes, they work so closely together that just contacting your state veterinarian is enough that they start the ball rolling and get USDA involved. After that, a lot of this is handled through the federal department as opposed to locally.
MC: Do you remember about how long the process was?
NJ: Pretty quick. From me reporting it to them quarantining the rescue, it was probably less than 48 hours. I made a call, left a message with state veterinarian’s office, and got a response back within a few hours. Then by the next day, the USDA veterinarian did contacted me and said, “Hey, tell me what you got, and here’s where I need you to send all those samples.”
MC: So are there vaccination options that exist to protect against RHDV2?
SB: Yeah, so thankfully, in October of 2020, we did get a USDA emergency approval for a vaccine from a company called Medgene. Prior to that, there were two vaccines available from Europe, one of which had been used a bit out west.
NJ: Historically the vaccines that were used at the very beginning of the spread of this in the United States were imported from France. There was a lot of welfare concerns with those vaccines, because they were actually created from the livers of harvested rabbits. And so a lot of people were very leery of that, because rabbits were sacrificed to create the vaccine. Granted, the scale was quite in favor of vaccination: One rabbit liver could provide enough vaccine for hundreds, if not thousands, of rabbits. But the Medgene vaccine is not—there are no rabbits that are slaughtered to make this vaccine, which is, I think, a really huge selling point.
SB: This particular vaccine is made here in the United States and has undergone fairly extensive testing for safety and efficacy. And if anyone’s interested, the Medgene website has a lot of data.
NJ: Granted, it’s an in-house study, so there’s some bias, but when they did their initial study, it was pretty fantastic. The placebo group mortality was like 70% and then the treatment group had zero after exposure to the virus. So the vaccine is, at least in that study, incredibly effective.
KB: Can you tell us a little more about the specifics of the vaccine: How it’s administered, how long it takes for an animal to be fully protected, the duration of immunity, anything practitioners should be aware of before they start using it?
SB: The vaccination is a low-dose vaccine as a 0.5cc subcutaneous injection, and it does require a booster 21 days later initially. Although we don’t have official recommendations on annual vaccination, everyone that I know across the country is recommending annual vaccines after that, which we’re now in the process of doing since it’s now been out for over a year.
This vaccine does come in 10-dose tanks, and due to the preservative in the vaccine, the manufacturer does recommend that once we open that bottle of vaccine that we use it same day or within 24 hours. So that has created a situation where for the safety of our patients, most of us have tried to at least vaccinate 10 at a time, or we have started encouraging the general public to bring their pet rabbits into vaccine clinics for vaccination.
I’ve probably personally vaccinated about 1,500 doses of vaccine with very little, if any, side effects so far. So in my hands, has been very safe, well tolerated, and it doesn’t appear to sting. I’ve vaccinated animals as young as 12 weeks of age. I haven’t really gone younger than that, but it’s actually approved at four weeks. I’m not quite that brave; I like my babies to be a little bit older. But that’s just my personal opinion. I’m probably more worried about the stress of vaccination in those youngsters than anything.
KB: Along those same lines, are there any patients that are not eligible to receive the vaccine and under what circumstances?
SB: So we do always screen our patients to make sure they’re a good candidate for vaccination, of course, and there’s been a few where I’ve chosen not to. But I’ve done as old as 10, 11 years old and even with concurrent health concerns—seizure patients, patients with chronic illnesses as long as they’re stable at that time—and had no repercussions that we’re aware of. But I’ve not done pregnant or nursing bunnies personally.
NJ: When Medgene did their safety study, I think they vaccinated nursing does, although I certainly haven’t done that. Just this past week, I actually did two 8-week old little lops by myself, and they didn’t flinch, didn’t even move after the injections.
KB: With such a short shelf life of the vaccine once you open it, what would you recommend for those practitioners who don’t see a lot of rabbits? Would it be better for them to refer out to an exotic vet such as yourselves?
NJ: The only sterility data they have on the vaccine was 24 hours. So you know, it’s it’s a tricky slope, right? If you have a 10-dose vaccine and you’re not going to see 10 rabbits in a day, you’re potentially losing out a lot on that. And I think in those circumstances, if you’re not really doing that many rabbits, have your folks talk to Dr. Borders’ vaccine clinic, because they’re doing them incredibly regularly and going through hundreds of vials at this point. You know, until we see that sterility data come out, anything you do outside of that is sort of at your own risk.
SB: I think safety of the patient has to be considered first. If someone’s interested in the vaccine, I think it’s important to find a rabbit-savvy vet, and if they aren’t in a position to offer in-clinic vaccination, then they can refer them to a local vaccine clinic. A lot of rescue groups that have vets that come in, and they sponsor vaccine clinics as well through these rescue groups. So from Cleveland to Cincinnati to Dayton, even in southern Ohio, there are other places where they’re having these vaccine clinics.
KB: As we know, most pet owners have more than one animal, and of course shelters and rescues have many animals to care for, too. Is this vaccine affordable, particularly for people who need to vaccinate multiple rabbits?
SB: I think there’s a fear of costs associated with vaccination. It isn’t an overly expensive vaccination, but it does take some time and education and resources to be able to administer it, even in a clinic setting.
NJ: A lot of times when we’re talking about the expense of vaccinating 50 or 100 rabbits, I think sometimes it’s easy to go, “Well, it’s just you know, the scale of economics is so challenging.” But also I think it’s important to keep in mind that, in order to administer and order this vaccine, the veterinarian also has to be USDA accredited. So there’s some additional training that’s required for the person administering the vaccine, and we shouldn’t forget about the fact that that requires some additional expense, unfortunately.
KB: It sounds like Europe and other parts of the world are way ahead of the U.S. in dealing with this virus, just because they got hit first. I’m curious, how is the rest of the world handling RHDV? Have other countries gotten it under control, or is it still spreading?
SB: My understanding is that the RHDV original serotype in Europe wasn’t contagious between wild rabbits to domestic rabbits, so I don’t feel like it was quite as aggressive. I feel like what we’re seeing with this RHDV2 serotype has really been significant.
NJ: It’s really interesting that these caliciviruses are independent strains of this virus. There’s even theory that RHDV2 was a non-pathogenic virus present of the rabbit population in Europe, and then it underwent a pathogenic mutation, and now it’s this huge problem and it’s become the predominant calicivirus affecting rabbits in multiple continents—Europe Australasia, North America, and I believe there’s even cases reported in South America.
SB: When this surfaced in Australia, it spread across the continent in less than two years. It was that rampant. And I think vaccination probably has been fairly prevalent out there for a longer period of time, even though I think it does also have some other potential side effects, too. And I don’t know how widespread they’re using it.
NJ: I know that they’ve had access to the vaccine for a longer period of time and they even have the RHDV1 vaccines available. And because they have other viral diseases that are endemic in those areas, they also combined the vaccine with other diseases, myxomatosis being the primary one. And so vaccination of rabbits is a routine part of the wellness care in those areas. In some areas, they are even recommending vaccination every six months rather than annually with the vaccines that are available. In Australia where it’s legal to own a rabbit—because it’s not in every territory in Australia; in some you’re not allowed to legally—they often vaccinate against this virus every six months.
KB: Before we wrap up, can you share any resources for our listeners who’d like to learn more about RHDV and the vaccine?
SB: I think good resources to learn more about RHDV would be the USDA. A lot of the veterinary colleges, too—like Cornell has some great information, since there’s been quite a bit in New York. I see some are a little more updated than others; I think it depends on if you’re in a hotbed or not. So going to areas where there’s more of a hot zone going on might be a great place to get updated information too.
NJ: Do you remember the name of that RHDV Facebook group where they’re talking about all the vaccine clinics?
SB: Yeah, Rabbit Hemorrhagic Disease News Network, it’s called. The admin on that seems to be pretty active and knowledgeable. She covers the wildlife side as well as the domestic rabbit side, and not only rescue partners, but breeders too. They list vaccine clinics all over the United States, and that’s where I get all my updated maps on current cases.
NJ: My favorite term for these sorts of situations is citizen scientists, right? Because they have this huge vested interest in in making sure their animals are healthy and well cared for, but they’re also seeking information or providing information in, we’ll say, a less-than-traditional veterinary outlet.
SB: Again, the vaccine has been well received and we’re out there as much as we can trying to educate the public to come in and get their rabbits vaccinated. You know, another area we’re trying to educate and get the vaccine out to is the agriculture side. The 4H kids are getting into that season. And I think that’s another area that really has to be focused on from an education perspective.
NJ: And the USDA made a really great fact sheet about RHDV where they list the disinfectants and the brand names and contact times and how to dilute them. So I think for practitioners who see rabbits or who are concerned about rabbits, it’s a good tool to have downloaded and potentially even as a handout for people that are involved with rabbit situations.
MC: Are there any other thoughts you guys wanted to share with us before we let you go?
SB: I just would like to really encourage everyone to learn as much as they can about rabbit hemorrhagic disease virus, even if they don’t see rabbits in their practice or necessarily see themselves carrying the vaccine. This is a disease that we’d like to get as much education out amongst the veterinary community and certainly the general public so that we can protect all rabbits, not just our pets. I really think there’s value to try and educate the general public, so that, one, we can identify potential cases like, you know, the average hiker that sees a deceased rabbit, and so we can do some additional screening and work on the big picture as much as possible.
NJ: Yeah, I would absolutely echo those those thoughts and sentiments. I think, too, for the practitioner that doesn’t really plan to see rabbits or doesn’t want to see rabbits—which is totally understandable; they’re kind of a finicky species to deal with. But if you look at the popularity of pet species across the world, even in North America, as you get beyond like cats and dogs as the two most popular pets, rabbits and bearded dragons fight for third place. More and more people have rabbits in their homes as pets, and so you’re probably going to receive more calls from people going, “I have a rabbit. I’m worried about this thing. Do you have any information?” So even if it’s just to say like, “Yeah, we don’t really see rabbits here, but we know what you’re talking about. Here are some people to contact and resources you could look at.” I think that that would serve you well, because many of those people also own cats and dogs. Very few people own just one pet.
KB: It’s never a bad thing to have more information and knowledge about something, especially like this.