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.

阐明病原体传播机制是预测疾病动态及其对宿主种群影响的核心前提。已有研究证实，引发壶菌病（chytridiomycosis）的两栖类真菌病原体蛙壶菌（Batrachochytrium dendrobatidis，简称Bd）可通过与感染宿主的直接接触实现传播。然而，其间接传播路径仍未得到充分探究。本研究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，旨在探究助产蟾（Alytes obstetricans）幼体的Bd传播路径。实验将未接触过病原体的易感蝌蚪分为两组：一组与感染Bd的蝌蚪共养（允许直接与间接传播），另一组则与未感染的蝌蚪共养（仅允许间接传播）。研究结果显示，与感染宿主的物理接触并非Bd初始感染的必要条件，且所有受试蝌蚪仅在四周后便全部感染。不过，与感染蝌蚪的物理接触可加速Bd在蝌蚪种群内的传播速度，并导致更高的Bd载量与后续更高的死亡率。本研究结果明确证实，在助产蟾种群中，即便不存在物理接触，Bd仍可在种群中快速扩散。因此，本实验强调了受感染湖泊中Bd游动孢子（zoospores）的间接传播对疾病动态的重要性，尤其当存在助产蟾这类储存宿主时，该传播路径的作用更为显著。