Data from: Amphibian chytridiomycosis in Japan: distribution, haplotypes, and possible entry into Japan

A serious disease of amphibians caused by the chytrid fungus Batrachochytrium dendrobatidis was first found in Japan in December 2006 in imported pet frogs. This was the first report of chytridiomycosis in Asia. To assess the risk of pandemic chytridiomycosis to Japanese frogs, we surveyed the distribution of the fungus among captive and wild frog populations. We established a nested PCR assay that uses two pairs of PCR primers to amplify the internal transcribed spacer (ITS) region of a ribosomal RNA cassette to detect mild fungal infections from as little as 0.001 pg (1 fg) of B. dendrobatidis DNA. We collected swab samples from 265 amphibians sold at pet shops, 294 bred at institutes, and 2,103 collected at field sites from northern to southwestern Japan. We detected infections in native and exotic species, both in captivity and in the field. Sequencing of PCR products revealed 26 haplotypes of the B. dendrobatidis ITS region. Phylogenetic analysis showed that 3 of these haplotypes were specific to the Japanese giant salamander (Andrias japonicus) and appeared to have established a commensal relationship with this native amphibian. Many other haplotypes were carried by alien amphibians. The highest genetic diversity of B. dendrobatidis was found in the American bullfrog (Rana catesbeiana). Some strains of B. dendrobatidis appeared to be endemic to Japanese native amphibians, but many alien strains are being introduced into Japan via imported amphibians. To improve chytridiomycosis risk management, we must consider the risk of B. dendrobatidis changing hosts as a result of anthropogenic disturbance of the host-specific distribution of the fungus.2006年12月，日本首次在进口宠物蛙中检出由蛙壶菌（Batrachochytrium dendrobatidis）引发的两栖动物严重病害，这是亚洲地区首次报道壶菌病（chytridiomycosis）。为评估大流行壶菌病对日本蛙类的威胁风险，本研究针对该真菌在圈养与野生两栖动物种群中的分布开展了调查。本研究建立了一套巢式PCR（nested PCR）检测方法：采用两对PCR引物扩增核糖体RNA转录单元的内部转录间隔区（ITS），可从低至0.001皮克（1飞克）的蛙壶菌DNA中检测到轻度真菌感染。研究共采集三类拭子样本：日本国内宠物商店售卖的265只两栖动物、科研机构繁育的294只两栖动物，以及从日本北部至西南部野外区域采集的2103只两栖动物样本。研究在圈养与野外环境的本土及外来两栖动物物种中均检出了真菌感染。对PCR产物的测序结果显示，蛙壶菌的ITS区域共存在26个单倍型（haplotype）。系统发育分析（phylogenetic analysis）表明，其中3个单倍型为日本大鲵（Andrias japonicus）所特有，且似乎与该本土两栖动物形成了共生关系。其余多数单倍型则由外来两栖动物携带。美洲牛蛙（Rana catesbeiana）体内的蛙壶菌遗传多样性最高。部分蛙壶菌菌株为日本本土两栖动物所特有，但另有大量外来菌株通过进口两栖动物传入日本。为优化壶菌病的风险管理策略，我们必须考虑到：人类活动干扰了该真菌的宿主特异性分布，可能导致蛙壶菌发生宿主转换，这一风险不容忽视。