Data from: Initiation of Batrachochytrium dendrobatidis infection in the absence of physical contact with infected hosts – a field study in a high altitude lake

Understanding transmission is a critical prerequisite for predicting disease dynamics and impacts on host populations. It is well established that Batrachochytrium dendrobatidis (Bd), the amphibian fungal pathogen responsible for chytridiomycosis, can be transmitted directly, through physical contact with an infected host. However, indirect pathways of transmission remain poorly investigated. We conducted a five-week long field infection experiment at a high altitude mountain lake in the French Pyrenees to investigate Bd transmission pathways in larval midwife toads Alytes obstetricans. Uninfected naïve tadpoles were co-housed either with infected tadpoles (direct and indirect transmission) or with uninfected ones (indirect transmission only). We found that physical contact with an infected host is not necessary for initial infection with Bd and that all tadpoles became infected after only four weeks. However, physical contact with infected tadpoles led to a faster spread within a tadpole group and resulted in higher Bd loads and subsequently higher mortality. Our findings clearly demonstrate that in A. obstetricans, Bd can quickly spread in a population even without physical contact. Our experiment therefore stresses the importance of indirect transmission of Bd zoospores in infected lakes for disease dynamics, especially when a reservoir species such as A. obstetricans is present.明晰病原菌传播路径，是预测疾病动态及其对宿主种群影响的核心前提。已有共识表明，引发壶菌病（chytridiomycosis）的两栖类真菌病原菌蛙壶菌（Batrachochytrium dendrobatidis, Bd）可通过与感染宿主的直接接触实现传播。然而，其间接传播路径迄今仍未得到充分研究。我们于法国比利牛斯山脉的一处高海拔山地湖泊开展了为期五周的野外感染实验，以探究助产蟾（Alytes obstetricans）幼体的蛙壶菌传播路径。将未感染的易感蝌蚪分为两组，分别与感染蝌蚪（允许直接与间接传播）或未感染蝌蚪（仅允许间接传播）混养。研究结果显示，即便不与感染宿主发生直接接触，蝌蚪也可初始感染蛙壶菌，且仅需四周所有受试蝌蚪均被感染。不过，与感染蝌蚪的直接接触可加速蛙壶菌在蝌蚪种群内的传播，并导致更高的蛙壶菌载荷量，进而提升死亡率。本研究结果明确证实，在助产蟾（A. obstetricans）种群中，即便不存在直接接触，蛙壶菌也可在种群中快速扩散。因此，本实验强调了感染湖泊中蛙壶菌游动孢子（zoospores）的间接传播在疾病动态中的重要性，尤其当存在助产蟾这类储存宿主物种时。