James Gorman

There’s another deadly virus outbreak in the U.S., but this one is killing thousands of wild rabbits. It started in New Mexico in March and has since spread to Texas, Arizona, Colorado, Nevada, California and Mexico. It poses a fatal threat to pets as well as wild animals.

The illness is caused by Rabbit Hemorrhagic Disease Virus type 2 and does not affect humans or other animals, only rabbits, hares and perhaps pikas, a rabbit-like animal, according to the U.S. Department of Agriculture. It is not a coronavirus.

This is the first outbreak of the virus in wild rabbits in North America, but there have been other, smaller outbreaks among domestic rabbits in Ohio, Washington and New York, and in feral rabbits in Canada — pets that have escaped or been released and continue to breed. The pet and feral animals are descendants of European rabbits, not native to North America.

Ralph Zimmerman, the state veterinarian in New Mexico, where the new outbreak started, said its origin is unknown. But, he added, imported domestic rabbits are one possibility; the disease was first identified in France in 2010 and spread throughout Europe and later Australia, where it swept the continent in about a year and a half. An outbreak at a New York veterinary clinic in March of this year killed 11 pet rabbits.

“We hear rumors of underground rabbit transport, and there are folks that do import rabbits from Europe,” Dr. Zimmerman said. “So our concern is that somebody brought them in, they were carrying the virus during transport. If one of them died, they pitched it out and boom, we infect the wild rabbits and away we go.”

Not much can be done about wild populations of rabbits, Dr. Zimmerman said. Many die, and some survivors that are resistant to the virus repopulate the area. How much of the wild population dies will determine the impact of the disease on predators that rely on rabbits.

The virus is a variant of the original R.H.D.V., which emerged in China in 1984 and spread through Asia, Europe and North and South America. When it escaped in Australia, scientists there were studying it for possible use in controlling rabbit populations. It has been killing rabbits in Australia ever since, although R.H.D.V. type 2, the new virus, took over and became the dominant strain.

It is both highly infectious, and extraordinarily sturdy. According to the federal National Wildlife Health Center, it can survive several months in dry conditions, lives through freezing and can be spread by rabbits, their pelts or their meat, or anything that has come in contact with them, including insects. Often, rabbits simply drop dead.

The disease poses a serious danger to domestic rabbits. Last year the agriculture department estimated that nearly three million U.S. households had about 6.7 million pet rabbits. There is a vaccine for the disease approved in Europe, and states, in concert with the agriculture department, can approve its use, which has happened in New Mexico, Dr. Zimmerman said.

But vaccine approval could come too late for a rabbit owners, because there must be a confirmed rabbit death in order for a veterinarian to begin applying for emergency approval in any given state, said Anne Martin, executive director of the House Rabbit Society.

And like any virus, this one has an incubation period; by the time rabbits begin to die, the virus is already spreading, and the vaccine still must then be imported once the approval paperwork is done.

To be safe, rabbits, like people, need to be isolated. There are also other precautions to take, Ms. Martin said, because the virus can survive for so long, but “the biggest risk to rabbits is if they are outside or they have any outdoor playtime.”

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