Ixodid tick Dermacentor reticulatus

A report from South Korean public health officials has confirmed the return of a potentially fatal viral disease in East Asia. The first case of serious infection with a tick-borne virus called SFTS — short for severe fever with thrombocytopenia syndrome — was reported in Jeju City on April 9. The disease, which shares its name with the virus, first surfaced in China in 2009, and each year has brought with it an increasing number of cases.

A Tick Bite Alert, warning against the ixodid tick species that are the main vectors of the virus, is in effect in South Korea after a 40-year-old man tested positive for the virus, reported Outbreak News Today on Sunday. The Chinese scientists that first wrote about it in 2011 in the New England Journal of Medicine listed the symptoms of infection as “fever, fatigue, chill, headache, lymphadenopathy, anorexia, nausea, myalgia, diarrhea, vomiting, abdominal pain, gingival hemorrhage, conjunctival congestion, and so on.” Severe cases can be fatal. When it was first discovered, the virus was identified as a never-before-seen species of Bunyavirus, a family of viruses known to use insects, ticks included, as their transmission vectors. The number of cases that have been reported in South Korea, China, and Japan has increased sharply in the past nine years.

texas longhorn cattle
The virus that causes SFTS is transmitted by ticks that infect livestock.

As Nature News reported Monday, South Korea saw 270 reported cases last year, a large jump from the 36 it saw in 2013; China jumped from 71 cases in 2010 to 2,600 cases in 2016, and between 2016 and 2017, Japan saw a 50 percent increase in cases. Fortunately, increased awareness about virus symptoms and prevention methods has led to a drop in the fatality rate. “In China, only around 3% of people infected died in 2016, and in Japan the number fell to 8%. In South Korea, the figure dropped from 47% in 2013 to 20% in 2017,” reports Nature News.

Characterization of the symptoms has identified some of the warning signs of severe illness as fever, thrombocytopenia (a low platelet count), and leukocytopenia (a low white blood cell count). The people who are most at risk are those who aren’t sure they were bitten by a tick, the authors of the 2011 NEJM study noted. The virus-transmitting ticks are thought to infect livestock, which are the original hosts of the virus. People in regular contact with such animals and those who work in agriculture or forestry are advised to get checked out if they have any of the associated symptoms, even if they don’t know if they’ve been bitten by a tick.

Scientists are already working on drugs to treat infection, but treatment options can’t come soon enough, as there seems to be a link between the changing climate and number of SFTS cases. A 2017 article in Scientific Reports suggested that warmer, more southerly regions see more cases and have a longer epidemic duration, and an Ecology and Evolution paper in 2014 presented evidence that the ixodid ticks that carry the virus have “some potential to adapt to climate change.”

Fortunately, the disease can’t be spread from human to human, as far as we know, although the virus surprised officials when it appeared to have spread through bites from a cat and from a dog in 2017. Clearly, there’s plenty we still need to learn about the virus — and we need to do it quickly.