Highly contagious and deadly rabbit disease found in western US, including California

A deadly virus is threatening to wipe out entire populations across multiple states. At risk are North America's rabbits.

It's a strain of Rabbit Hemorrhagic Disease, and it's recently appeared in pockets of the Western US. If it continues to spread unchecked, it could harm all dozen-plus species of rabbits in the US and the ecosystems they belong to.

The highly contagious illness isn't connected to coronavirus -- only rabbits, hares and pikas, the diminutive cousin of rabbits, can spread it among each other, and humans can't become infected with it.

Rabbit Hemorrhagic Disease virus type 2 can cause internal bleeding and swelling, but more often, the sickened rabbits aren't discovered until they've already died, according to the California Department of Fish and Wildlife.

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There are some parallels between Rabbit Hemorrhagic Disease and Covid-19, said Matt Gompper, a disease ecologist and head of the Department of Fish, Wildlife and Conservation Ecology at New Mexico State University.

Both are thought to have "spilled over" from one species to another -- in the case of the novel coronavirus, likely a bat to humans; in the rabbit disease, from domestic to wild rabbits -- and both arose so quickly that health officials had a limited window to act.

How the disease came to the US

The disease likely originated around a decade ago in European rabbits, which comprise most domestic rabbits sold in the US, Gompper said.

Then, in early March, another strain of the virus was discovered in wild rabbits in southern New Mexico. A few days later, dead rabbits were spotted nearby in El Paso, Texas. More sightings followed in Arizona, Colorado and, in May, in California.

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Ecologists aren't sure how virus type 2 arrived in the US. Gompper said he predicts the disease worked its way through rabbit meat or the domestic rabbit trade. It also might have been circulating in northern Mexico, which shares a border with New Mexico and Texas.

The disease could harm ecosystems

Because the illness is so new, there's virtually no data on the related die-offs, Gompper said. So while it's still concerning, ecologists aren't sure if the illness will cause concentrated outbreaks in local areas or widespread deaths across the US.

Either way, it's a loss for conservation. Several rabbit species, including California's Riparian brush rabbit, are endangered or vulnerable, and they're already up against habitat loss. A potentially fatal disease could hobble their recovery.

Rabbits aren't the only ones who'd suffer, though. If rabbit populations deplete, then the predators who prey on them would lose a valuable food source, and the plants they graze on may overgrow, sending tremors throughout the ecosystem, Gompper said.

"Rabbits, wherever they're found, tend to have a relatively robust impact on their environment because they're primary herbivores," he said. "Whether the impact of the virus is such that we'll see those very dramatic ecological changes as a result is still an unknown."

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