Wetland virus found in 17 Chinese people
Chinese virologists have described a virus that was first isolated in 2019 from a patient after a tick bite in a swampy park. It turned out to be a member of the genus Orthonairovirus (Orthonairovirus) from the family Nairovroviridae. As reported in The New England Journal of Medicine, it has been dubbed the wetland virus, and its infection has been reported in 17 other patients in northeastern China.
Several new human tick-borne viral infections have emerged in the last decade: for example, severe fever virus with thrombocytopenia syndrome, Heartland virus or Alongshan virus. Some of the new viruses belong to the Orthonairovirus genus of the family Nairoviridae, which also includes the causative agents of Congo-Crimean hemorrhagic fever, Dugbe virus and Nairobi sheep disease virus. Apart from Congo-Crimean hemorrhagic fever, the other infections are relatively easily transmitted. However, they are of public health importance because of their wide host range and geographic distribution.
A team of scientists led by Wei Liu of the Beijing Institute of Microbiology and Epidemiology described a potentially pathogenic orthonairovirus that was first detected in June 2019 in a 61-year-old hospitalized man. He was bothered by fever, headache, malaise, vomiting and enlarged lymph nodes. He recalled being bitten by ticks during a recent trip to the swampy park of Yakeshi (Inner Mongolia), about 5 days before the onset of illness. Despite antibiotic therapy, his condition progressively worsened due to multi-organ dysfunction. Sequencing of serum samples showed infection with a previously unknown orthonairovirus, which the scientists named swampy virus. Its presence was further confirmed by polymerase chain reaction.
The scientists then conducted a field study of ticks and other blood-sucking insects in northeastern China, focusing on the wetland park where the ticks had bitten the first patient. They also observed patients with similar symptoms at nearby hospitals. Swampy virus was detected in several ticks and found to possess a single-stranded three-stranded negative sense RNA genome encoding an L-protein, a glycoprotein precursor, and an N-protein. The L, M, and S segments showed typical end reverse complementary sequences seen in orthonairoviruses. Comparison of nucleotide and amino acid sequences showed that marshland virus was more closely related to Hazara orthonairoviruses than to other genogroups of orthonairoviruses and had the highest sequence similarity to tofla virus.
A total of 682 febrile patients underwent PCR testing for marshland virus, 17 were positive, all of whom were geographically distributed in northeastern China. The mean duration from symptom onset to hospitalization was five days. On admission, the 17 patients had nonspecific symptoms such as fever, dizziness, headache, malaise, muscle and joint pain, and back pain. Gastrointestinal manifestations (nausea, vomiting, and diarrhea) were observed in 53 percent of patients.
Commonly observed laboratory abnormalities on admission included decreased lymphocyte, platelet, and white blood cell counts and elevated levels of C-reactive protein, fibrinogen, d-dimer, lactate dehydrogenase, and liver enzymes. In four patients, antibodies specific to marsh virus could be detected in the blood. All patients recovered and were discharged four to 15 days (average eight) after hospitalization.
Since the scientists further confirmed the infectivity of the virus through experiments in mice, as well as its cytopathic effect on human umbilical vein endothelial cells, marshland virus can be considered a new pathogenic orthonairovirus. Further studies will address the epidemiology of the virus, although already in this work the researchers have detected virus RNA in five species of ticks, sheep, horses, pigs, and the Transbaikalian tsokor (Myospalax psilurus).