Scientists in China identify new tick-borne virus behind unexplained fevers

Researchers in China have identified a previously unknown tick-borne virus that appears to explain thousands of cases of unexplained fever, fatigue and gastrointestinal illness in patients who had tested negative for a better-known and more dangerous tick-borne disease. The pathogen, described in a report published Sept. 28 in the New England Journal of Medicine, has been named Asian longhorned tick nairovirus, or ALTNV, after the invasive tick species that carries it.

The discovery grew out of a diagnostic puzzle that had frustrated clinicians in China for years. Roughly 30 percent of patients who arrived at hospitals with symptoms consistent with severe fever with thrombocytopenia syndrome, a tick-borne illness caused by Dabie bandavirus, tested negative for that virus on standard panels even though their symptoms matched. Investigators at the State Key Laboratory of Pathogen and Biosecurity in Beijing set out to find what else might be making these patients sick, and landed on a virus that had not been catalogued before.

The numbers

The research team tested blood samples from 3,163 patients with fever and a history of tick exposure. Overall, 10.4 percent tested positive for ALTNV, based on viral RNA or antibodies. Among patients who had already tested negative for Dabie bandavirus, the positive rate for the new virus rose to 15.1 percent. Patients infected with ALTNV alone reported fatigue in 84 percent of cases, gastrointestinal symptoms in 80 percent, low platelet counts in 38 percent and elevated liver enzymes in 36 percent. Every one of them recovered.

The picture was different for the 38 patients who were infected with both ALTNV and Dabie bandavirus. Those coinfected patients more often developed respiratory symptoms — 61 percent, compared with 38 percent among patients with Dabie bandavirus alone — and kidney impairment, 84 percent versus 66 percent. Seven of the 38 coinfected patients died, an 18.4 percent fatality rate in that group, though the study did not find that ALTNV alone caused severe bleeding or death. Separately, researchers screened more than 47,000 ticks collected across 15 Chinese provinces and detected ALTNV in 1.3 percent of them overall, rising to 1.8 percent among Haemaphysalis longicornis, the Asian longhorned tick that lends the virus its name.

How a new virus family member surfaced

ALTNV belongs to Orthonairovirus, a genus of tick-borne viruses that also includes Crimean-Congo hemorrhagic fever virus, one of the more lethal pathogens tracked by global health authorities. Most orthonairoviruses circulate quietly between ticks and wild or domestic animals and only occasionally spill over into people, which helps explain why new members of the family keep turning up even in places with established disease surveillance. The Center for Infectious Disease Research and Policy at the University of Minnesota, summarizing the findings, noted that genetic sequencing showed ALTNV was distinct enough from previously known orthonairoviruses to warrant classification as a new species.

The tick that carries it is not confined to China. Haemaphysalis longicornis is native to East Asia but has spread far beyond it over the past century, becoming established in Australia, New Zealand and several Pacific island nations, and more recently in the United States, where it was first detected on a sheep farm in New Jersey in 2017. It has since become a reproducing, overwintering population confirmed in roughly 15 states along the East Coast and into parts of the Midwest and South. The species is notable for its ability to reproduce asexually, meaning a single female tick can found an entire new population without a mate.

Who is affected, and the reaction

So far, confirmed ALTNV infections are limited to patients in China, and researchers on both sides of the Pacific stress there is no evidence the virus is circulating in American ticks. Physicians at Stony Brook Medicine said the discovery should not alarm the public but does underscore the value of telling a doctor about recent tick bites or outdoor exposure when fever, unusual fatigue or a rash develop, since that history helps narrow diagnostic testing.

"This discovery is a wake-up call. Doctors had thousands of patients showing classic tick-borne symptoms — but testing negative for every virus we knew about," Dr. Tyler Evans, an infectious disease physician and chief executive of the Wellness Equity Alliance, said in comments reported by Newsweek.

The study's authors, writing in the journal, said the overlap of ALTNV and Dabie bandavirus in the same ticks and the same regions of China "underscores the need for improved differential diagnosis between infections with these viruses" in areas where the more severe disease is endemic. In practical terms, that means hospitals in affected provinces may need broader testing panels rather than assuming a single familiar virus explains every fever following a tick bite.

What happens next

Public health researchers say the immediate priorities are surveillance and clarification. Investigators want to know how widely ALTNV has already spread among ticks and animal hosts, whether it is present in the other countries where the Asian longhorned tick has become established, and whether coinfection with Dabie bandavirus — rather than ALTNV on its own — is what drives the more severe outcomes documented in the coinfected patients. None of those questions can be settled by a single case series, and the study's authors have called for expanded testing of both patients and tick populations in affected regions.

For now, the practical guidance for people in areas where the Asian longhorned tick is established, including much of the eastern United States, has not changed: use tick repellent as directed, wear long clothing tucked in when walking through grass or brush, check for ticks after time outdoors, and remove any attached tick promptly with fine-tipped tweezers. Whether ALTNV itself eventually turns up in American ticks remains an open question, but its discovery gives clinicians one more reason to take unexplained fevers after a tick bite seriously.