Concern rises over deadly tick-borne virus in Japan

February 20, 2013

THE ASAHI SHIMBUN

A newly identified deadly virus probably transmitted by blood-sucking ticks is causing concern after experts confirmed it in Japan only a few years after it first surfaced in China.

To date, there have been four deaths in Japan. The latest is that of a man who died last summer in Hiroshima Prefecture after contracting "severe fever with thrombocytopenia syndrome" (SFTS), the Hiroshima prefectural government said Feb. 19.

SFTS was first reported in China in 2009. Scientists identified the virus behind it in 2011.

Figures put the mortality rate at 12 percent in China.

The disease was first detected in Japan in late January this year. A physician researching the unexplained death of a woman last autumn in Yamaguchi Prefecture asked the National Institute of Infectious Diseases to test blood samples.

Following a positive identification, the health ministry called for information on other suspected cases nationwide and gathered blood and other samples.

Pathologists identified further cases on Feb. 13 and attributed the deaths last autumn of two men from Ehime and Miyazaki prefectures to SFTS. All four cases occurred in western Japan.

There is now concern nationwide. Medical institutions and public health centers have made about 30 inquiries with the health ministry. Ministry officials said samples from nine suspected cases await testing.

The disease has an incubation period of between six days and two weeks. Symptoms then emerge, which may include fever, diarrhea and stomachache. There may also be a reduction in the concentration of blood platelets and white blood corpuscles.

In all four confirmed deaths, the patients died one to two weeks after developing symptoms. At the time, doctors were unable to establish the cause of death, and none of the victims had traveled overseas immediately prior to infection, the ministry officials said.

How the four patients in Japan contracted SFTS remains unclear. No traces of tick bites were found on their bodies. Moreover, the SFTS virus has not been found in ticks in Japan.

In China, the virus was found in 5.4 percent of ticks sampled in endemic areas, which suggests ticks are the vectors.

Ticks typically live in grassland, and 97 percent of SFTS infections identified in China involved farmers in mountainous areas. Rat mites and house dust mites do not carry the SFTS virus.

The viruses found in the four Japanese who died had an almost identical genetic profile, but it differed slightly from the genome of the Chinese strain.

Masayuki Saijo, director of the Department of Virology I at the National Institute of Infectious Diseases, said the virus had likely been in Japan for some time.

"I don't believe that these deadly viruses emerged out of the blue," Saijo said. "A sharp increase in infections is improbable."

More than 200 people in China are thought to have contracted the disease so far, according to Chinese figures. No vaccines or palliative drugs exist, so treatment is centered on symptomatic therapy, such as alleviating fever and stanching bleeding.

Ticks are widespread across Asia and Oceania. Usually measuring only a few millimeters in size, an adult tick bloats to resemble a blueberry nearly 1 centimeter wide after gorging on the blood of its host.

THE ASAHI SHIMBUN
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The tick that likely carries the virus behind "severe fever with thrombocytopenia syndrome" (SFTS) (Provided by the Department of Medical Entomology, National Institute of Infectious Diseases)

The tick that likely carries the virus behind "severe fever with thrombocytopenia syndrome" (SFTS) (Provided by the Department of Medical Entomology, National Institute of Infectious Diseases)

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  • The tick that likely carries the virus behind "severe fever with thrombocytopenia syndrome" (SFTS) (Provided by the Department of Medical Entomology, National Institute of Infectious Diseases)

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