BEIJING—Scientists aren't entirely sure how it infects people or how it kills, but researchers now at least know the face of their enemy. In an article posted online on 16 March in The New England Journal of Medicine (NEJM), a Chinese team describes a new virus that appears to cause a lethal disease, severe fever with thrombocytopenia syndrome (SFTS).
The virus's identification "is a prime example of the rapid discovery of a truly emerging infectious disease and its cause," Heinz Feldmann of the National Institute of Allergy and Infectious Diseases's Laboratory of Virology in Hamilton, Montana, writes in an accompanying editorial in NEJM. But the pathogen, a bunyavirus, is still something of a mystery.
SFTS came to light in 2006, when villagers in Anhui Province in central China began dying of an illness characterized by high fever, gastrointestinal distress, and a depressed platelet count. Researchers at the Chinese Center for Disease Control and Prevention (CDC) here suspected anaplasmosis, an infection spread by ticks caused by the bacterium Anaplasma phagocytophilum. But they found neither bacterial DNA nor antibodies against it. Each spring since then the disease has struck with a vengeance, killing up to 30% of those infected in six provinces of China.
In December 2009, Xue-jie Yu, an expert on tick-borne diseases at the University of Texas Medical Branch at Galveston, isolated from a patient's blood a new phlebovirus, part of the Bunyaviridae family that includes hantavirus and Rift Valley fever virus. Then last spring and summer, Chinese CDC researchers detected SFTS bunyavirus RNA, specific antiviral antibodies, or both in 171 out of 241 people hospitalized for SFTS. From these samples, Chinese CDC virologist Li Dexin and colleagues isolated 11 strains of the bunyavirus. The two teams initially made rival claims about who identified the virus first and planned to publish separate reports. China's health minister, Chen Zhu, brokered a compromise in which the two teams merged data in the NEJM article and shared credit for the discovery.
Like anaplasmosis, SFTS appears to be transmitted by ticks; 10 of 186 ticks collected in the region were found to carry SFTS bunyavirus RNA. (Scientists have found no trace of the virus in mosquitoes.) But only a small percentage of victims recall having been bitten. For that reason, says Chinese CDC Director Wang Yu, "We are not quite sure that ticks are the vector." Feldmann agrees. "The current data can only be seen as preliminary," he says. "There could be more than one tick [species] serving as the vector."
His agency will probe that question when SFTS presumably strikes this spring, and they will look for other organisms that may harbor the virus. They also hope to unravel puzzling aspects of the clinical course of the illness. It's unclear, says Wang, how the virus kills people. And some cases resembling SFTS may in fact be anaplasmosis, says Chinese CDC virologist Liang Mi-Fang. Anaplasmosis is treatable with antibiotics, highlighting the need for a rapid diagnostic kit to distinguish between the two villains.