MANSFIELD, Connecticut – A recently detected foreign pathogen is posing a significant threat to both wild and domestic rabbit populations in Connecticut, researchers say.

The Connecticut Veterinary Medical Diagnostic Laboratory (CVMDL) recently identified a domestic case of the Rabbit Hemorrhagic Disease Virus Type 2 (RHDV2) in the state. The CVMDL is part of the University of Connecticut’s College of Agriculture, Health and Natural Resources.

Dr. Guillermo Risatti, the director of the CVMDL, oversaw the lab’s identification of RHDV2.

“Whenever there is an outbreak – in this case a significant die-off of rabbits – most likely what happened is that the owner called the vet, the vet saw it as an unusual event and let the state know,” Risatti said. “Then the lab jumps in and has to conduct a foreign animal disease investigation.”

A spreading crisis

Dr. Emily Reinhardt is an associate director of the CVMDL and an assistant clinical professor of veterinary pathology at the University of Connecticut, or UConn. She added that the CVMDL had been monitoring regional cases of RHDV2 before the first case in Connecticut was brought to the lab for identification in September.

“It’s been informally on the radar of the lab for a while,” Reinhardt said.

As Risatti mentioned, the identified case of RHDV2 was sent to the CVMDL because a significant number of rabbits in a domestic population died in a short amount of time.

“Dr. Lewis, the state veterinarian, reached out to us to let us know the virus had been identified in New Jersey and that we should be on high alert,” Reinhardt said. “Soon after, she submitted to us the domestic case that was diagnosed as positive.”

According to Reinhard, the symptoms of RHDV2 are easily identifiable.

“The classic sign is the bloody nose,” Reinhard said. “The rabbit just dies suddenly, and often has a bloody nose.”

According to the USDA, the blood-stained nose is from internal bleeding that the virus causes. Infected rabbits may also develop a fever, be hesitant to eat or show signs of nervousness or respiratory issues.

Part of the concern over the disease is that RHDV2 is extremely contagious and often fatal to infected rabbits, Reinhardt said.

“It’s a more infectious variant of the classic Rabbit Hemorrhagic Disease Virus; the fatality rates are higher and it targets a wider age range of rabbit than the classic variation,” Reinhardt said. “There is a higher threat to wild species with this variation; it’s more dangerous.”

Wild rabbit populations already fragile

Much of the current concern regarding RHDV2 is the possibility of the disease entering Connecticut’s wild rabbit population, Reinhardt said. “The risk to Connecticut’s wild rabbit population relates to the disease’s high fatality rate.”

RHDV2 could also remain in the wild rabbit population as a reservoir, and perpetuate a cycle of transmission between wild and domestic populations, Reinhardt said. “It can be transmitted on fur, wood, animal droppings or urine, shoes or by pets, so there is risk to any domestic rabbit with access to an outside area.”

Other experts already had concerns regarding the state’s wild rabbit populations before the identification of RHDV2 in Connecticut.

Chadwick Rittenhouse, Ph.D., is an assistant professor in residence in the Department of Natural Resources and the Environment at UConn who has done extensive research on wild rabbit populations in the state.

There are two species of wild rabbit in Connecticut – the Eastern cottontail rabbit and the New England cottontail rabbit, Rittenhouse said in an interview. The New England cottontail is native, whereas the Eastern cottontail is invasive. Population numbers for the New England cottontail are already low, Rittenhouse said.

“The New England cottontail’s range is being overtaken by the Eastern cottontail,” Rittenhouse said. “They are very indistinguishable from each other, often we have to look at genetic information to tell the two apart or identify the species of a specific rabbit.”

In 2015 the New England cottontail was not considered an endangered species despite relatively low population numbers, Rittenhouse said. He says that now RHDV2’s rapid spread poses a greater threat to the New England cottontail species.

“So there is huge concern over this disease,” Rittenhouse said. “We know it can pretty much decimate a population, quite literally reduce it to one-tenth of its original size, as it did in the Southwestern United States and a few other places.”

Low population numbers for the New England cottontail rabbit mean that if the often-fatal RHDV2 disease gets into Connecticut’s wild rabbit population, it could lead to extinction.

“If Rabbit Hemorrhagic Disease wipes out a large proportion of the New England cottontail population, and there are not enough of them left to repopulate, it could be the end of the species in the wild,” Rittenhouse said.

The threat of extinction

This threat of extinction also has negative implications for other populations in the Connecticut ecosystem, he said.

“Rabbits are food for other species in the food chain,” Rittenhouse said. “If we snap a finger and all the rabbits are gone, their predators will have to switch prey, and therefore put pressure on other populations.”

These extinctions of one population in a food chain are often due to the effects of climate change. And extinctions don’t just impact one species – they disrupt the entire food chain and surrounding ecosystem, experts say.

Still, extinction threatens many animal and plant species each year. Mark Urban, a biologist and associate professor of ecology and evolutionary biology at UConn, highlighted the importance of reducing extinction rates and maintaining biodiversity.

“I think it’s a mistake that we just monitor species and populations to extinction,” Urban said. “We need to do something about it, rather than just watching them decline.”

But experts say that there are limited outcomes for RHDV2 and Connecticut’s rabbit populations at the moment.

Miranda Davis, Ph.D., a wildlife ecologist and assistant professor in residence in the Ecology and Evolutionary Biology Department at UConn, said the spread of RHDV2 to the wild rabbit population could be devastating.

“When we get a novel disease or disease variant introduced to a system, oftentimes the host species have very little resistance,” Davis said. “This is particularly true if the host species is a dense population, like rabbits, and the disease can easily spread like wildfire.”

According to Davis, the hope regarding most threatening diseases is that they become endemic, like the flu in the human population.

“There isn’t necessarily a way to entirely get rid of it, but it also doesn’t kill individuals at a high enough rate to wipe itself out,” Davis said. “The population just has to deal with it.”

A proactive solution

Experts say a large part of preventing extinctions via novel diseases relates to disease identification. This work is done in labs like the CVMDL.

Risatti explained that the CVMDL is a member of the United States Department of Agriculture’s National Animal Health Laboratory Network. One of the lab’s main goals is to respond to disease events such as this one quickly.

While RHDV2 has not been identified in Connecticut’s wild rabbit populations yet – the only positively identified case in the state was in domestic rabbits – the threat of this happening remains. And RHDV2 is likely too fatal to hold out hope for reaching an endemic level, Rittenhouse said.

“The best solution we know of right now is the vaccine,” said Rittenhouse, referring to the RHDV2 vaccine available from Europe. State agencies are looking at getting this vaccine to where it is needed in Connecticut, before the disease reaches the state’s wild rabbit populations.

“It’s not feasible to catch and administer a vaccine to all the wild rabbits in Connecticut, but we can give it to our contained or domestic rabbit populations as a start,” Rittenhouse said.