Department of Infectious Disease Epidemiology, Imperial College London W2 1PG, UK.
Ecol Lett. 2010 Mar;13(3):372-82. doi: 10.1111/j.1461-0248.2009.01434.x. Epub 2010 Jan 27.
Amphibian chytridiomycosis is a disease caused by the fungus Batrachochytrium dendrobatidis (Bd). Whether Bd is a new emerging pathogen (the novel pathogen hypothesis; NPH) or whether environmental changes are exacerbating the host-pathogen dynamic (the endemic pathogen hypothesis; EPH) is debated. To disentangle these hypotheses we map the distribution of Bd and chytridiomycosis across the Iberian Peninsula centred on the first European outbreak site. We find that the infection-free state is the norm across both sample sites and individuals. To analyse this dataset, we use Bayesian zero-inflated binomial models to test whether environmental variables can account for heterogeneity in both the presence and prevalence of Bd, and heterogeneity in the occurrence of the disease, chytridiomycosis. We also search for signatures of Bd-spread within Iberia using genotyping. We show (1) no evidence for any relationship between the presence of Bd and environmental variables, (2) a weak relationship between environmental variables and the conditional prevalence of infection, (3) stage-dependent heterogeneity in the infection risk, (4) a strong association between altitude and chytridiomycosis, (5) multiple Iberian genotypes and (6) recent introduction and spread of a single genotype of Bd in the Pyrenees. We conclude that the NPH is consistent with the emergence of Bd in Iberia. However, epizootic forcing of infection is tied to location and shaped by both biotic and abiotic variables. Therefore, the population-level consequences of disease introduction are explained by EPH-like processes. This study demonstrates the power of combining surveillance and molecular data to ascertain the drivers of new emerging infections diseases.
两栖动物壶菌病是由真菌蛙壶菌（Batrachochytrium dendrobatidis，Bd）引起的疾病。Bd 是一种新出现的病原体（新病原体假说；NPH），还是环境变化加剧了宿主-病原体动态（地方性病原体假说；EPH），这一点存在争议。为了厘清这些假说，我们在伊比利亚半岛以第一个欧洲暴发地点为中心，绘制了 Bd 和壶菌病的分布情况。我们发现，在两个采样点和个体中，无感染状态是常态。为了分析这个数据集，我们使用贝叶斯零膨胀二项式模型来检验环境变量是否可以解释 Bd 的存在和流行率以及疾病（壶菌病）发生的异质性。我们还使用基因分型搜索伊比利亚地区 Bd 传播的特征。我们表明：（1）Bd 的存在与环境变量之间没有任何关系的证据；（2）环境变量与感染的条件流行率之间的关系很弱；（3）感染风险存在阶段性异质性；（4）海拔与壶菌病之间存在很强的关联；（5）伊比利亚存在多种基因型；（6）在比利牛斯山脉，Bd 的单一基因型最近出现并传播。我们的结论是，NPH 与 Bd 在伊比利亚的出现是一致的。然而，感染的流行压力与位置有关，并受到生物和非生物变量的影响。因此，疾病传入的种群水平后果是由类似于 EPH 的过程来解释的。本研究展示了结合监测和分子数据来确定新出现传染病驱动因素的力量。
