Scientists find new virus behind mysterious tick illness
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Scientists in China have discovered a previously unknown tick-borne virus that can cause a flu-like illness involving fever, fatigue, gastrointestinal (GI) symptoms, and unusual laboratory results.
Researchers led by the State Key Laboratory of Pathogen and Biosecurity in Beijing have named the newly identified orthonairovirus Asian longhorned tick nairovirus (ALTNV).
The discovery, reported in the New England Journal of Medicine, grew out of efforts to understand why about 30% of patients with symptoms suggestive of Dabie bandavirus (DBV) infection test negative for the tick-borne hemorrhagic fever.
A Search for the Cause of Unexplained Tick Illness
DBV causes severe fever with thrombocytopenia syndrome (SFTS), a potentially deadly disease found across Asia. The infection has a case-fatality rate of 10% to 30%. Thrombocytopenia refers to an abnormally low level of platelets, the blood cells involved in clotting. The World Health Organization has identified DBV as a priority pathogen for research.
To investigate unexplained cases, researchers collected samples from people who had been bitten by ticks and were treated at sentinel hospitals in regions of China where tick-borne viruses are known to circulate. Using RNA sequencing and viral isolation, the team detected the previously unknown virus.
“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.”
Genetic analyses placed ALTNV within the orthonairovirus genus in the family Nairoviridae. Its proteins shared less than 80% of their amino acids with those of other species in the genus, supporting its identification as a distinct virus.
Researchers also exposed laboratory cells to human serum containing ALTNV RNA. The virus grew in the cells and was identified as ALTNV using immunofluorescence to detect viral antigens. Electron microscopy revealed features typical of orthonairoviruses, while additional experiments showed that the virus could replicate in several types of cells.
ALTNV Found in More Than 10% of Patients Tested
Among 3,163 patients included in the study, 10.4% tested positive for ALTNV based on the presence of viral RNA or immunoglobulin M antibodies, which can indicate a recent infection.
The proportion was even higher among people who tested negative for DBV. In that group, 15.1% were positive for ALTNV.
Among patients infected only with ALTNV, the most common symptom was fatigue, reported by 84%. Gastrointestinal (GI) problems occurred in 80%, while 38% developed thrombocytopenia. Elevated aminotransferase concentrations were found in 36% (indicating inflammation or injury of the liver or other tissues; 36%). These patients ultimately recovered completely.
Coinfections Were Linked to More Severe Complications
Researchers also identified 38 patients who were infected with both ALTNV and DBV.
Compared with people infected only with DBV, those with both viruses experienced respiratory symptoms more often, affecting 61% compared with 38%. Kidney impairment was also more common in coinfected patients, occurring in 84% compared with 66%.
Seven of the 38 coinfected patients died, representing 18.4% of that group.
Virus Detected in Ticks Across 15 Provinces
The researchers also tested 47,428 ticks collected from 15 provinces. ALTNV RNA was present in 1.3% of them.
The highest prevalence was found in Haemaphysalis longicornis, commonly known as the Asian longhorned tick, with 1.8% testing positive.
Laboratory experiments provided further evidence that this tick species can spread the virus. Researchers showed that H longicornis was capable of transmitting ALTNV to mice.
Because ALTNV and DBV occur in the same regions and can be spread by the same tick vector, the researchers say distinguishing between the two infections could become increasingly important.
“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.
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