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.

明晰病原体传播途径，是预测疾病动态及其对宿主种群影响的核心前提。现已明确，引发壶菌病的两栖类真菌病原体蛙壶菌（Batrachochytrium dendrobatidis, Bd）可通过与感染宿主的直接物理接触实现传播。然而，其间接传播途径仍未得到充分研究。本研究在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Bd传播途径。将未接触过病原体的易感蝌蚪分为两组：一组与感染Bd的蝌蚪混养，可同时发生直接与间接传播；另一组仅与未感染的蝌蚪混养，仅可发生间接传播。研究发现，与感染宿主的物理接触并非Bd初始感染的必要条件，且仅需四周，所有受试蝌蚪均已被感染。但与感染蝌蚪的物理接触可加速Bd在蝌蚪种群中的传播，并导致更高的Bd载量，进而提升死亡率。本研究结果明确证实，即使不存在物理接触，Bd仍可在助产蟾种群中快速传播。因此，本实验强调了受感染湖泊中Bd游动孢子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主物种时。