Scientists in China, led by the State Key Laboratory of Pathogen and Biosecurity in Beijing, have discovered a previously unknown tick-borne orthonairovirus named Asian longhorned tick nairovirus (ALTNV), which causes a flu-like illness characterized by fever, fatigue, gastrointestinal symptoms, and unusual laboratory results. 
A finding reported in the New England Journal of Medicine that emerged from efforts to understand why about 30% of patients with symptoms suggestive of Dabie bandavirus (DBV) infection test negative for the tick-borne hemorrhagic fever responsible for severe fever with thrombocytopenia syndrome (SFTS), a potentially deadly disease with a case-fatality rate of 10% to 30% where thrombocytopenia refers to an abnormally low level of platelets, the blood cells involved in clotting, and the World Health Organization has identified DBV as a priority pathogen for research. 
To investigate these 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 to detect the previously unknown virus, while genetic analyses placed ALTNV within the orthonairovirus genus in the family Nairoviridae with proteins sharing less than 80% of their amino acids with those of other species in the genus to support its identification as a distinct virus, and laboratory experiments exposing cells to human serum containing ALTNV RNA showed the virus grew and was identified as ALTNV using immunofluorescence to detect viral antigens. 
With electron microscopy revealing features typical of orthonairoviruses and additional experiments showing that the virus could replicate in several types of cells. 
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, and the proportion was even higher among people who tested negative for DBV, in that group, 15.1% were positive for ALTNV, while 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, and elevated aminotransferase concentrations were found in 36% (indicating inflammation or injury of the liver or other tissues; (36%), and these patients ultimately recovered completely. 
Researchers also identified 38 patients who were infected with both ALTNV and DBV, and compared with people infected only with DBV, those with both viruses experienced respiratory symptoms more often, affecting 61% compared with 38%, and kidney impairment was also more common in coinfected patients, occurring in 84% compared with 66%, with seven of the 38 coinfected patients dying, representing 18.4% of that group. 
Furthermore, the researchers also tested 47,428 ticks collected from 15 provinces where ALTNV RNA was present in 1.3% of them, and the highest prevalence was found in Haemaphysalis longicornis, commonly known as the Asian longhorned tick, with 1.8% testing positive, while laboratory experiments provided further evidence that this tick species can spread the virus by showing 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, and as the authors concluded, "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."