マダニが媒介する感染症「SFTS」が西日本を中心に拡大している。2014年7月時点で、日本国内では感染者の3割が死亡。予防用のワクチンや治療薬は存在しない。9月11日には、デング熱の国内感染者が100人突破するなど感染が拡大しているが、SFTSにも警戒が必要だ。
SFTSの正式名称は、「重症熱性血小板減少症候群」。SFTSウイルスを持つマダニに咬まれることで、人間に感染する。2011年に新種のウイルスとして中国の研究者が確認したのを皮切りに、中国で大流行した。日本でも2013年1月に初確認され、西日本を中心に感染が急拡大。2014年に入ってから感染者数が半年間で、前年を超えるなど患者数が急増している。
SFTS症例の発生（感染）地域（N=85, 2014年7月30日現在）
国立感染症研究所によると、7月30日現在で国内の感染者数は85人。そのうち3割に当たる26人が死亡した。西日本の16県で報告され、60代以上の感染者が特に多く全体の9割を占めている。東京都感染症情報センターでは、症状を次のように説明している。
主な症状は発熱と消化器症状（おう吐、下痢など）が中心で、倦怠感、リンパ節腫脹、出血症状なども見られます。潜伏期間は6日～2週間で、致死率は約10～30％（中国では2009年当初の報告例が少なく致死率は30数％でしたが、その後の調査により10数％と推定されています）
（東京都感染症情報センター「重症熱性血小板減少症候群（SFTS）」より）
フタトゲチマダニ（国立感染症研究所）
マダニは人家にいるイエダニと違って山林に多く生息する。イエダニよりも体長は大きく3〜8ミリ程度。吸血後は1～2センチまで膨らむ。普段はネズミや小鳥、ウサギ、シカなどの体を吸血している。
春から秋にかけて活動するのが特徴。野山をハイキングする際には半袖などの肌をさらす格好を避けたり、虫よけスプレーを使うのが効果的だ。国際感染症センター医師の忽那賢志氏は次のように話している。
【関連記事】「山などに入る場合は、なるべく肌を晒さないことが肝要です。また、DEET（ディート）と呼ばれる化合物が含まれる虫よけスプレーを使用することも効果的です。ただし、日本で発売中のスプレーの濃度は最高でも12％で効果の持続は約2時間。長時間、野山に入る場合は2時間ごとに虫よけスプレーを使用する必要があります」
（日刊SPA!「デング熱よりも怖い!? マダニが介する致死率33%の感染症」より 2014/09/02）
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