In December 2018, a 53-year-old woman showed up at a hospital in China with flu-like symptoms. She was infected with a henipavirus, a class that includes some dangerous pathogens like Nipah virus, which has a fatality rate of 40% to 75%.
But the virus infecting the patient was genetically distinct from the other henipaviruses scientists had seen before. It came from a novel pathogen now known as Langya virus.
Scientists detected 34 more Langya cases across two eastern Chinese provinces through 2021, according to findings published last week by a research team in China, Singapore and Australia. None of the patients died.
Because of that, scientists aren't yet alarmed. There’s also no sign of human-to-human transmission; the patients who were studied didn’t seem to spread the virus to close contacts, nor did they have histories of common exposures. So Langya appears to be causing infrequent, sporadic infections, and it is most likely passed from animals to people.
Most patients had close contact with animals before they got sick, according to Zhu Feng and Tan Chee Wah, research fellows at Duke–National University of Singapore Medical School who coauthored the paper.
Still, other henipaviruses that spread from animals to humans can cause severe outcomes. Hendra virus, which can lead to respiratory illness or brain inflammation, has a fatality rate of 57%. Nipah virus produces similar symptoms.
"This is from a family of viruses that we know are concerning, and it appears that this group has now added a new lineage of viruses that are capable of severe disease," said Vaughn Cooper, an evolutionary biology professor at the University of Pittsburgh who wasn’t involved in the research. Increased surveillance is likely to detect more cases of Langya, he said.
The virus looks different from the Hendra and Nipah viruses, said Peter John Hudson, a biology professor at Penn State who studies the pathogens.
"It’s closely associated with the henipaviruses, but it might not even be in that family," he said.
Shrews or fruit bats might be the animal host
Feng and Chee Wah said the patients' symptoms were "relatively mild," though four developed pneumonia.
All of the reported cases had fevers. Around half experienced fatigue, cough and muscle pain. Roughly one-third developed nausea, headache, vomiting and impaired liver function. Two patients had impaired kidney function.
The research team suggested that shrews — small, mouselike mammals that feed on insects — might be natural hosts for Langya virus. After examining 25 species of small wild animals, the team found that 27% of shrews had Langya virus, which was the highest share for any species in the research.
"There are clearly repeated transmission events from what looks to be a common reservoir in shrews," Cooper said. "The team did a very nice job of evaluating alternatives and finding that as the most likely explanation."
Reservoir hosts are species in which a virus circulates, often without ill effects, that can pass it to humans or other animals. But shrews aren't an obvious animal host because of their short life expectancy, Hudson said.
"At this stage, we don’t know what the reservoir host is," he said. "My expectation would be that it would be a flying fox.”
Flying foxes are fruit bats, and Hendra and Nipah virus are known to originate in them. In the case of Hendra virus, the virus is usually passed from bats to horses; it then infects humans through the animals' excretions or bodily fluids.
People can catch Nipah virus from bats or pigs through direct contact with the animals, their bodily fluids or contaminated food. There have also been some "small, stuttering chains" of human-to-human Nipah transmission, Hudson said.
Hudson hypothesized that flying foxes could pass the virus to rodents or shrews, which could then go on to spread it to humans. Cooper guessed that people might also get exposed through contact with the droppings of infected animals, but scientists haven't determined that to be true yet.
Feng and Chee Wah said they also "could not eliminate the possibility that dogs and goats can be an intermediate host," since they detected the virus in 2% of goats and 5% of dogs studied.
Scientists could find more henipaviruses in the future
Cooper said it's an achievement that researchers detected Langya virus without a reported death.
"Normally it takes severe outcomes to motivate a group to find a new virus, and although these are hospitalized patients, there are no fatalities, so it’s a credit that they chased it down," he said.
Hudson attributed the discovery, in part, to robust disease tracking efforts.
"Since the first outbreak of SARS, we saw a big increase in surveillance in China of a number of these viruses. With the development of new techniques for identifying viruses, there’s certainly been a global increase in surveillance, and this has accelerated in the past five years," Hudson said.
But even so, both experts said, many unstudied and undocumented henipaviruses are likely to be circulating in animals.
Ideally, scientists would identify new pathogens before they spill over into people, Hudson said: "If you’re going to prevent the next pandemic, you actually have to stop these processes of it getting from reservoir hosts to humans."