New Tick-Borne Virus May Explain Mysterious Cases of Severe Illness

Researchers in China have identified a new tick-borne virus that may explain some previously unexplained cases of severe, hemorrhagic-fever-like illness. The virus, named Asian longhorned tick nairovirus (ALTNV), was described in a study led by the State Key Laboratory of Pathogen and Biosecurity in Beijing and published in the New England Journal of Medicine.

Among 3,163 patients tested in areas where tick-borne viruses circulate, 10.4% showed evidence of ALTNV infection. Among patients who tested negative for Dabie bandavirus (DBV) -- which causes severe fever with thrombocytopenia syndrome (SFTS), a tick-borne disease with a reported fatality rate of 10% to 30% that the World Health Organization lists as a research priority -- 15.1% tested positive for ALTNV instead. About 30% of patients with signs and symptoms suggesting DBV infection test negative for that virus, prompting the search for another cause.

Using RNA sequencing and viral isolation, the researchers identified ALTNV as a distinct virus within a group called orthonairoviruses, sharing less than 80% amino acid similarity with other species in the same genus. They confirmed it could reproduce in cultured cells, detected its viral antigens by immunofluorescence testing, and observed features characteristic of orthonairoviruses under electron microscopy.

Among patients infected only with ALTNV, fatigue was the most common symptom (84%), followed by gastrointestinal problems (80%); 38% developed thrombocytopenia and 36% had elevated aminotransferase levels, but all patients with ALTNV alone recovered completely. Among 38 patients coinfected with both ALTNV and DBV, outcomes were more severe: 61% developed respiratory symptoms (compared with 38% of patients with DBV alone) and 84% had kidney impairment (compared with 66% with DBV alone); seven of the 38 coinfected patients died, an 18.4% fatality rate in that group.

The researchers also tested ticks collected across 15 Chinese provinces and detected ALTNV RNA in 1.3% of 47,428 ticks, with the Asian longhorned tick (Haemaphysalis longicornis) showing the highest prevalence at 1.8%. Laboratory experiments showed this tick species could transmit ALTNV to mice. "The cocirculation of ALTNV and DBV in the same areas, coupled with their shared tick vector, underscores the need for improved differential diagnosis between infections with these viruses in regions where SFTS is endemic," the authors concluded.