In June 2012, three men removing slag from a derelict copper mine in southwestern China fell ill with severe pneumonia and died. Six months later, researchers went spelunking in the mine—an artificial cave hewn from a hillside—in search of pathogens. After taking anal swabs from bats, rats, and musk shrews living in the cave, the team has discovered what it says is a new virus that may have felled the workers.

The presumed pathogen resembles a genus of viruses known as henipaviruses, two of which are deadly: Hendra virus, discovered 20 years ago in Australia when it started killing horses—since then, four people who came in contact with infected horses have died—and Nipah virus, the cause of periodic outbreaks in people in Southeast Asia since 1998. The third confirmed henipavirus, Cedar virus, was first reported in Australia in 2012; it does not appear to infect humans. For all three species, the animals that harbor the virus in the wild—the natural reservoir—appear to be fruit-eating bats called flying foxes.

The new virus, named Mojiang paramyxovirus (MojV) after the county in Yunnan province where it was found, joins a growing list of species that share genetic similarities with henipaviruses and members of the Paramyxoviridae family that includes henipaviruses. The bats and shrews in the Yunnan cave tested negative for the new henipa-like virus; three of nine rats were infected. “It is not totally surprising to find henipa-like sequences in rodents,” as rats are the natural reservoir for some paramyxoviruses, says Lin-Fa Wang of the Australian Animal Health Laboratory in Geelong, who was not involved in the Mojiang study. MojV “could be a ‘bridging’ virus between those in bats and rodents,” says Wang, one of the leaders of the team that discovered Cedar virus.

The three victims in Yunnan succumbed long before scientists arrived on the scene, so “we have not established a direct relationship between human infection and MojV,” says Qi Jin, director of the State Key Laboratory for Molecular Virology and Genetic Engineering in Beijing, and leader of the new work, reported in the June issue of Emerging Infectious Diseases. The new virus and any relatives, if they exist, are keeping a low profile. Jin’s team sampled bats from the cave in Mojiang a second time and again came up empty. More recently, he says, a “systemic viral survey” in 38 bat species across China conducted by his team failed to turn up any henipaviruses. He believes rodents should be further investigated as potential wildlife reservoirs of henipavirus. But for the time being, Jin says, MojV is “more likely a curiosity.”