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Southwest US faces lethal rabbit disease outbreak

First time in nation rabbit hemorrhagic disease virus type 2 confirmed in wild species

April 14, 2020 (published)
By Lisa Wogan

This story has an important update

Photo by Dr. J.P. Teifke, Federal Research Institute for Animal Health, Riems, Germany. Courtesy of the Center for Public Health at Iowa State University College of Veterinary Medicine
Rabbit hemorrhagic disease causes lesions in afflicted rabbits' internal organs and tissues, resulting in bleeding. Upon death, rabbits may have a bloody nasal discharge.

In the first verified cases in wild rabbits in the United States of a highly contagious viral disease that causes sudden death in rabbits, the bodies of five desert cottontails and one black-tailed jackrabbit in New Mexico tested positive early this month for rabbit hemorrhagic disease virus type 2 (RHDV2).

The development was followed by more bad news from neighboring states. The Arizona Game and Fish Department announced on Saturday that RHDV2 had killed wild jackrabbits and cottontails within its borders. Wild rabbit die-offs are also being reported in western Texas, according to the U.S. Geological Survey's National Wildlife Health Center. The Texas Parks and Wildlife Department has submitted samples to determine the cause of death, according to a Texas Animal Health Commission spokesperson.

Testing in New Mexico followed reports of die-offs among wild rabbits in southern and eastern parts of the state. People called local game wardens to report seeing large numbers of dead rabbits, said Dr. Kerry Mower, a wildlife disease specialist for the New Mexico Department of Game and Fish.

"They were lying out in the open, not undercover and hidden," he said, which suggests the rabbits died quickly. One person on horseback came across so many bodies, the whole area was filled with the odor of dead animals, Mower said. He didn't know how many rabbits were found dead in each instance, but he said, "It's going to add up to tens of thousands across the landscape."

As of Tuesday, RHDV2 had been confirmed in domestic rabbits in 11 of New Mexico's 33 counties as well as in one county each in Arizona and Texas.

Reports of a deadly, highly infectious disease outbreak sound like a sinister echo of the COVID-19 pandemic. However, unlike the novel coronavirus that causes COVID-19, RHDV2 is not zoonotic and has no known impact on human health.

There are three major viral subtypes of RHD. The first form of RHD, caused by RHDV, first appeared in the U.S. in 2000. The disease caused by the viral subtype 2 was first identified in France in 2010. It subsequently spread widely among domesticated and wild rabbits in Europe, where it causes significant losses. It also has been found in Australia. In March 2018, RHDV2 was reported in domestic rabbits and feral rabbits in southwestern British Columbia, not far from the Canada-U.S. border. Feral rabbits are domesticated rabbits that have been abandoned or escaped outdoors.

The first documented cases of RHDV2 in the U.S. occurred among domestic rabbits in rural Ohio, on a farm south of Cleveland, in September 2018. The virus hit the San Juan Islands in Washington state in summer 2019. It also was identified in a group of rabbits at a veterinary hospital in New York City in March. (See Path of rabbit hemorrhagic disease.)

The developments in the Southwest mark a new phase in the course of RHD. The approach in the U.S. and Canada has been eradication: Isolate cases as they arise, and contain them. The strategy is predicated on the belief that containment was feasible because RHD hadn't shown up in wild rabbits. Further, it was thought that wild rabbits weren't susceptible. When the virus becomes established in wild rabbit populations, a different approach is required.

"The fact that this is in multiple counties and rabbitries, that's why this is so concerning," said Eric Stewart, executive director of the American Rabbit Breeders Association. "And then to hear it's burning through the wild rabbit populations, that, of course, furthers our concerns that much more."

State and provincial veterinarians agree that RHDV2 is likely to persist in British Columbia, Washington and New Mexico and eventually be considered endemic, meaning that it will regularly occur in those regions.

According to New Mexico State Veterinarian Dr. Ralph Zimmerman domestic rabbits found to be affected in that state were mostly kept for 4-H, showing and meat for personal use. Each group contained between five to 30 rabbits, he said. The state required any surviving rabbits be euthanized,and  affected premises disinfected and left unused for 90 days, he said.

Serendipitously, the COVID-19 human pandemic may help mitigate the spread of RHDV2 because rabbit shows and other rabbit-related events are canceled. "That does help us as far as limiting contact and transmission within our community," Stewart said. "But we're looking to get ahead of this for when these restrictions are lifted and people are able to travel again."

What is rabbit hemorrhagic disease?

The pathogen that causes rabbit hemorrhagic disease belongs to the calicivirus family. Caliciviruses infect a wide variety of animals, including cats, pigs, cattle, and humans. Norovirus which causes gastrointestinal disease, is a common calicivirus that afflicts people. There are many strains of RHDV and three major viral subtypes: RHDV (sometimes RHDV1 or "classical RHDV"), RHDVa and RHDV2. The clinical signs of the disease don't vary between subtypes but RHDV and RHDVa, which are closely related, have shorter incubation periods and higher mortality rates than RHDV2, as detailed in a 2016 report from Iowa State University.

Rabbits can contract the virus through contact with infected rabbits or with other animals or materials — such as food, water, bedding and vehicles — that have been in contact with infected animals. According to the U.S. Department of Agriculture, a very low dose, possibly as little as a few viral particles, is enough to cause infection. The virus is highly stable, especially in organic materials, and can remain viable for months in varied temperatures and over distances, enabling it to be spread by biting insects.

Stewart, who raises rabbits for Angora wool on a farm in Pennsylvania, is vigilant about avoiding spreading the disease. Returning home from a recent trip to England, where RHD is endemic, "I literally stripped down on my porch," he said. "All of my clothes from my luggage and my person immediately went into the washer." He didn't even walk up his sidewalk in the shoes he'd worn during his trip. "That's probably a bit of overkill, but I didn't want to risk anything."

Vaccines exist for RHD but are not approved for commercial use in the U.S. or Canada. Absent a vaccine, the best way to protect rabbits is with enhanced biosecurity practices, such as not sharing equipment with other rabbit owners; and disinfecting all equipment, such as waterers and feeders, that come into contact with rabbits. Treatment is generally limited to supportive care, with infected rabbits isolated from all other animals.

Although RHD does not pose a threat to humans, other animals or the food supply, the World Organisation for Animal Health, an international group based in France that tracks and disseminates information about animal diseases, requires that cases be reported by member countries, which includes the U.S. and Canada.

The time from infection to first signs of disease may be up to nine days. Affected rabbits may develop a fever and die within 36 hours. Infected rabbits may appear dull and be reluctant to eat; have congested membranes around the eyes; show signs of nervousness, incoordination or excitement; and/or make paddling movements. They may have trouble breathing. Upon death, they may have a blood-stained, frothy nasal discharge.

Infection with the RHD virus causes lesions throughout internal organs and tissues, particularly the liver, lungs and heart, resulting in bleeding. Mortality rates range between 40% and 100% for RHDV/RHDVa and 5% and 70% for RHDV2.

Evolving picture of susceptibility

Path of rabbit hemorrhagic disease

Scientists long have known that Oryctolagus cuniculus, a rabbit species that is both wild and domesticated in Europe, is susceptible to RHD. This is the only species of rabbit to have been widely domesticated worldwide, and all types of commercially bred or farmed rabbits in the United States are genetically related.

Before the cases in New Mexico, American wildlife species such as the cottontail (Sylvilagus audubonii), snowshoe hare (Lepus americanus) and black-tail jackrabbit (Lepus californicuswere thought not to be susceptible to the virus, according to the USDA.

Unlike the wild rabbits that tested positive in Arizona, the cause of death of the wild rabbits found positive in New Mexico has not been determined definitively through necropsy or histology, according to Dr. Kerry Mower, a wildlife disease specialist for the New Mexico Department of Game and Fish. However, RHDV2 is the presumed cause of death for several reasons, he said.

The numerous reports of large scale mortality among wild rabbits "was on a wider scale geographically and more prevalent than I have ever seen in tularemia," Mower said, referring to an infectious disease caused by the bacterium Francisella tularensis, which initially was suspected. The agency ruled out tularemia based on an examination of the livers of some of the dead rabbits. 

Mower explained that other conditions that might kill off rabbits, such as parasites, don't move like viruses. "I can't see it as being anything else," he said. Another important factor in the determination was timing because the wild die-off coincided with the deaths of domestic rabbits in the area due to RHDV2.

Mower said Game and Fish is working with the National Wildlife Health Center in Madison, Wisconsin, and the USDA to determine the course of surveillance and testing of New Mexico's wild population going forward.

In Arizona, Dr. Anne Justice-Allen, wildlife veterinarian in that state's Game and Fish Department, necropsied three wild rabbits from three different locations in southwestern Arizona. "All had lesions consistent with RHDV2. Two were sent to FADDL [Foreign Animal Disease Diagnostic Laboratory], and RHDV2 was confirmed," Justice-Allen said in an email to the VIN News Service. Three additional specimens will be submitted tomorrow.

FADDL is the USDA's animal disease center on Plum Island, New York. It is the only laboratory in the country that tests for the RHD virus.

Justice-Allen said on Monday the known infections in cottontails and jackrabbits is limited to Cochise County, which shares a border with New Mexico. "We would like it to stay that way but don't expect it to, with a detection in domestic rabbits in Springerville," Justice-Allen said, referring to an unverified report from a breeder in a town in Apache County. In addition, 15 domestic rabbits died due to RHDV2 in Navajo County last week.

Justice-Allen added that it is not known if the Springerville case is connected to the domestic rabbit cases in New Mexico. "We have not had any mortality of cottontails in Springerville reported to us," she said. "Field personnel are on the lookout for mortality events, are collecting specimens when appropriate and notifying me right away."

Vaccines come to Canada

The presence of RHDV2 in feral and wild rabbit populations has increased calls for vaccines in affected areas. RHD vaccines are not approved for commercial use in the U.S. or Canada. They are produced in Europe, where the virus is endemic. Filavac is effective against both the original variant of RHD and RHDV2. Eravac is effective only against RHDV2.

A third vaccine, Nobivac Myxo-RHD, protects against RHDV1 and myxomatosis, a virus carried asymptomatically by wild rabbits and spread by biting insects that is fatal to domestic rabbits. A fourth vaccine, Nobivac Myxo-RHD Plus, was approved in December 2019 and is not yet commercially available. It protects against classical RHDV and RHDV2 and myxomatosis.

Filavac is widely used in pet rabbits in the United Kingdom and continental Western Europe, and Eravac is primarily used in the rabbit-meat farming industry, said Dr. Tom Donnelly, a research professor in exotics at the National Veterinary School at Alfort, Maisons-Alfort, France.

New Mexico's Zimmerman is working with the USDA to authorize veterinarians in his state to import and use one of the vaccines. A few veterinarians in Washington and Canada have been permitted to buy Filavac on a provisional basis.

Dr. Adrian Walton is one. He owns a companion animal hospital in Vancouver, British Columbia, with a special focus on exotic animals, especially rabbits. When news of RHDV2 in domestic rabbits and feral colonies in and around Vancouver began circulating in 2018, "there was a considerable amount of panic," Walton said.

He immediately reached out to Filavie, makers of Filavac, and provincial authorities. He chose Filavac because he found commercial rabbitries were not interested in vaccinating for RHD.

For commercial breeders or farmers with many rabbits, the cost of vaccinating can be prohibitive.

Initially, Walton intended to order more vaccines than he would need, intending to distribute them to other veterinarians. He wasn't allowed to do that because the conditional-use permits restrict use to individual clinics. He ordered 300 doses in 2018, 200 for last year and he has 100 for this year.

However, British Columbia's chief veterinary officer at the time, Dr. Jane Pritchard, arranged to import vaccines through the province's animal health center, which are being provided to practitioners in affected areas. Walton called Pritchard a "hero" for organizing the import.

In 2018 and 2019, 13,530 doses of vaccine were delivered to 78 practices, and so far this year, 4,150 doses have been distributed, according to Dr. Brian Radke, public health veterinarian for British Columbia Ministry of Agriculture.

When the VIN News contacted Walton, he had been focusing on COVID-19-related issues and missed the news from New Mexico. "The fact that it's jumped to our native rabbits scares the crap out of me," he said.

A solo mission in the Pacific Northwest

Photo by Leah Miyamoto
Possibly the first rabbit in the United States to be vaccinated for rabbit hemorrhagic disease virus types 1 and 2, Sienna belongs to Leah Miyamoto, a veterinary technician at the Center for Bird and Exotic Animal Medicine in Bothell, Washington. The practice owner, Dr. Alicia McLaughlin, applied for and received special permission to import the vaccine from Europe. Vaccines for RHD are not approved for sale in the U.S. or Canada.

Unlike in Canada, deploying a vaccine in Washington was driven by a single veterinarian working on her own time: Dr. Alicia McLaughlin, who is the co-medical director of The Center for Bird and Exotic Animal Medicine in Bothell, Washington. North of Seattle, Bothell is not far as the seagull flies from RHDV2 hotspots in Western Washington.

Since RHDV2 was first identified there last summer, there have been more than a half-dozen incidents affecting domestic and feral rabbits. The state issued an emergency rule restricting the movement of rabbits, rabbit products, rabbit equipment and crates in order "to contain the disease before it spreads further onto the mainland and becomes endemic in Washington," according to the state agriculture department.

Dr. Susan Kerr, an education and outreach specialist for the state Department of Agriculture, said large die-offs of feral rabbits were reported on four islands. "The die-offs were noticeable because there were huge and problematic populations of feral domestic rabbits in those areas, so people noticed when they didn't see feral rabbits anymore," Kerr wrote in an email to VIN News. "Sick ferals probably went into burrows and died there; very few bodies were found, the ferals were just gone."

Stories like this circulated among rabbit owners, and McLaughlin soon had quite a few clients requesting the vaccine.

She started the process to get a permit last September, reaching out to the USDA and Kerr. It took several frustrating weeks to figure out the application process, she said. Around Thanksgiving, she received her permit and ordered vaccine directly from Filavie. She wired money from her personal account and hired a customs broker to shepherd the order of more than 500 vaccines, shipped in a temperature-controlled box. They arrived in January.

The combined cost of the vaccines, shipment, and hiring the broker was $8,000, she said, and does not include her time or the cost of staffing clinics.

"Dr. McLaughlin cannot be praised enough for her persistence and dedication to importing the vaccine," Kerr said. "It was a very onerous process, and most others who tried gave up. She was a pioneer!" Two other veterinarians have since been approved to import the vaccine.

As part of the approval, before McLaughlin could provide vaccinations to her waiting list of clients, she had to hold vaccination clinics in areas where the movement of rabbits has been restricted due to the virus. She held three vaccination clinics in February. On Whidbey Island, she vaccinated 87 rabbits in one day.

So far, she has used about half of her vaccine stock. She continues to offer vaccinations during the COVID-19 shutdown because RHDV2 is so virulent. She said she is able to minimize the risk of exposure to the COVID-19 virus by pet owners and clinic personnel by having pets dropped off by and returned to their owners at curbside.

Most owners have been grateful for the vaccine. McLaughlin said she often hears some version of: "No one else cared enough about our bunnies." However, she said some rabbit owners were upset she was charging more than the vaccine cost in France.

She charged $35 for the vaccine plus a group exam rate of $30 for up to three rabbits and $100 for four or more rabbits. "Most felt the value was worth the cost," she said.

Filavac requires an annual booster, so McLaughlin realizes protecting rabbits will require ongoing effort. "If we continue to see cases, I'll have to go through this process again," she said.

Update: Colorado and Texas join New Mexico and Arizona as states reporting rabbit hemorrhagic disease virus type 2 in dead wild rabbits. According to announcements the week of April 20 from the Colorado Department of Agriculture and Texas Parks and Wildlife, three wild cottontails in southern Colorado, a wild cottontail in western Texas and a black-tailed jackrabbit in the Texas Panhandle have tested positive for RHDV2.

May 19 update: RHDV2 has been reported in two more states. The virus was confirmed on April 30 in domestic rabbits that died suddenly at a household in Las Vegas, according to the Nevada Department of Agriculture. In California, a black-tailed jackrabbit carcass discovered on private property near Palm Springs in early May was diagnosed with RHDV2, according to the California Department of Fish and Wildlife.

June 26 update: RHDV2 has been diagnosed in a domestic rabbit in Sanpete County, Utah, according to an announcement from Utah Department of Agriculture and Food.

Correction: This story has been changed to correct the approval dates on the Nobivac Myxo-RHD and Nobivac Myxo-RHD Plus vaccines.


VIN News Service commentaries are opinion pieces presenting insights, personal experiences and/or perspectives on topical issues by members of the veterinary community. To submit a commentary for consideration, email news@vin.com.



Information and opinions expressed in letters to the editor are those of the author and are independent of the VIN News Service. Letters may be edited for style. We do not verify their content for accuracy.



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