Rabbit Hemorrhagic Disease: Deadly Virus Found in U.S. Highly 'Concerning'

The United States is currently experiencing a multi-state outbreak of a highly infectious and lethal disease that affects rabbits. But what is this disease and how has it spread across the country?

Rabbit hemorrhagic disease, as it is known, is caused by a form of viral hepatitis that can affect hares and rabbits—in other words, animals that belong to the group called lagomorphs.

According to Andrew Di Salvo, a wildlife veterinarian with the Pennsylvania Game Commission, the viruses that cause rabbit hemorrhagic disease (RHD) currently fall within three distinct pathogenic groups: RHDV, also referred to as classic RHDV or RHDVa; RHDV1, which is a subtype of RHDV; and RHDV2, sometimes referred to as RHDVb.

"While North American lagomorphs do not appear to be susceptible to the other groups of viruses, they and lagomorphs of European lineage—most rabbits kept as pets or as livestock fall into this category—are highly susceptible to RHDV2," Di Salvo told Newsweek.

The virus was first documented in France in 2010 and has since spread across Europe, parts of the Mediterranean, the Middle East, Asia, New Zealand, Australia, and the United States.

RHDV2 was initially detected in the United States in domestic rabbits in 2018 in Ohio, according to William Wepsala, a public affairs specialist with the U.S. Department of Agriculture's (USDA) Animal and Plant Health Inspection Service. A few sporadic outbreaks in domestic and feral rabbits followed that one in 2019 and early 2020 in Washington and New York.

In April 2020, the virus was found in wild lagomorphs in the southwestern United States, including New Mexico, which was the starting point for the current multi-state outbreak. There are now a total of 28 states, primarily in the Southwest and West, with RHDV2 detections amid the outbreak, affecting domestic, feral and wild lagomorphs. Additional RHDV2 cases have also recently been detected in Ontario and Alberta in Canada.

"The source or means of introduction of the disease in our current multi-state outbreak is unknown," Wepsala told Newsweek.

According to Di Salvo, RHDV2 is "extremely hardy"—it is very resistant to temperature extremes and can survive for long periods of time in the environment—as well as being "highly contagious." Infected hares or rabbits can shed the virus in their secretions (respiratory and salivary, for example) and excretions (such as feces and urine.)

"The disease can spread between hares and rabbits via many pathways that include direct contact with an infected live or dead hare or rabbit; ingestion of contaminated food or water; inhalation; contact with contaminated equipment, tools and enclosures; viral movement by flies, birds, biting insects, predators, scavengers and humans; and contact with urine, feces and respiratory discharges from infected individuals," Di Salvo said.

"The virus can survive on clothing, shoes, plant material, or other items that could accidentally be moved from an infected area."

While RHDV2 does not impact human health, recent detections of the virus demonstrate the role people are playing in the spread of disease, according to Di Salvo. For example, humans can spread the virus indirectly by carrying it on their clothing and shoes.

"Due to its highly contagious nature and many transmission routes, RHD can spread very quickly," Di Salvo said. "In addition to RHDV2 being highly contagious, mortality rates following infection often exceed 70 percent. It is extremely concerning."

Often, the only symptoms of the disease are sudden death and blood-stained noses caused by internal bleeding, although infected animals may also develop a fever, be hesitant to eat, or display respiratory or nervous signs.

Early in the current outbreak, the disease spread outward from the affected areas in a contiguous pattern, according to Wepsala. But recently the disease has made geographic jumps into domestic rabbits distant from the known infected areas. This indicates some risk pathways that aren't completely understood.

"Because of this, strict biosecurity measures are essential to prevent introduction of the virus to new areas including sanitation and disinfection, the maintenance of closed colonies or isolating new rabbits entering a rabbitry, and care with sourcing feed that might be contaminated," he said.

"Early in the outbreak, spread was rapid. In 2022, spread was more sporadic and characterized by geographic jumps into new areas," Wepsala said.

The ease with which the virus can spread and the fact that it can persist for months in the environment makes eradication of the disease in the wild following introduction inherently challenging, according to Di Salvo.

"Cleaning and disinfection is not possible in a wild setting, so wild lagomorph populations must often naturally develop immunity before populations can recover," he said.

"Any disruption of wild lagomorph populations can have significant ecological implications, so we are working diligently to educate the public on the threat RHD poses to not just Pennsylvania's snowshoe hare, Appalachian cottontail, and Eastern cottontail rabbit populations, but to all the wild animals and wild habitats within the Commonwealth."

Aside from being highly contagious, lethal and hardy, Wepsala said RHDV2 is concerning as an emerging disease because it has a wide host range, which includes both domestic and wild rabbits. In addition, there is no treatment for affected rabbits.

"In areas where the disease is present in wild populations, there are a number of threatened and endangered wild rabbits at risk," Wepsala said.

Compounding the problem until last year was the fact that easily available tools to fight the disease were unattainable.

At the beginning of the current outbreak, the USDA's Center for Veterinary Biologics (CVB) allowed importation of European-licensed RHDV2 vaccines. But importing these vaccines was expensive and logistically challenging. Then in September 2021, a U.S.-based company received emergency use authorization for an RHDV2 vaccine.

"This vaccine has various levels of approval for use in 45 states and has made an important tool for prevention much more available to rabbit owners," Wepsala said. "The company is working with CVB to obtain a conditional license."