Abstract：
The crayfish plague pathogen Aphanomyces astaci has been implicated in a number of mass mortalities and irreversible population declines of native crayfish across Europe. At present, the reservoirs of the pathogen in Europe are mainly populations of invasive North American crayfish species. In southwestern Europe, including France, a particularly widespread invader is the red swamp crayfish Procambarus clarkii. Recent distribution data confirm that P. clarkii is present in at least 75 French departments, i.e. more than 78% of those in metropolitan France. We analysed the prevalence and pathogen load of A. astaci in 42 populations of this species in western France (Nouvelle Aquitaine region), where the species is most densely distributed, particularly in a wide range of environments around the Gironde estuary. The pathogen was detected by two different quantitative PCR assays in more than three quarters of the populations studied (34 out of 42); 163 out of 480 analysed crayfish individuals tested positive for the presence of A. astaci. In most cases, individual infection levels were very low, detectable with quantitative PCR but not sufficient for pathogen genotyping. In seven P. clarkii individuals from four populations, however, we were able to assess A. astaci variation by microsatellite markers and sequencing of mitochondrial markers. All these host specimens carried A. astaci genotype group D, haplotype d1, which has caused the majority of crayfish plague outbreaks in neighbouring Spain. In contrast, the French outbreaks genotyped to date (including eight newly analysed in this study) were mostly caused by strains of genotype group B, specific to the signal crayfish Pacifastacus leniusculus. Haplotype d1 found in P. clarkii was involved in one of the newly characterised outbreaks. Our study confirms that P. clarkii is a potentially important reservoir of the crayfish plague pathogen in France, but not the main source of the pathogen in mass mortalities of A. pallipes, probably due to different ecological requirements of the different invasive host crayfish. However, as P. clarkii continues to spread, the threat posed by this species to native crayfish is likely to increase.
摘要：
小龙虾鼠疫病原体阿phanomycesastaci与欧洲本地小龙虾的大量死亡和不可逆转的种群减少有关。目前,在欧洲，病原体的水库主要是入侵的北美小龙虾种群。在欧洲西南部,包括法国,一种特别普遍的入侵者是红色沼泽小龙虾Procambarusclarkii。最近的分布数据证实，克拉氏疟原虫至少存在于75个法国部门，即超过78%的法国大都市。我们分析了法国西部（NouvelleAquitaine地区）该物种42个种群中的A.astaci的患病率和病原体负荷，物种分布最密集的地方，特别是在吉伦德河口周围的各种环境中。通过两种不同的定量PCR测定法在所研究的四分之三以上的种群中检测到了病原体（42个中的34个）；480个被分析的小龙虾个体中，有163个被测试为存在A。在大多数情况下,个体感染水平非常低，用定量PCR检测，但不足以进行病原体基因分型。在四个种群的七个克氏疟原虫个体中，然而,我们能够通过微卫星标记和线粒体标记测序来评估A.astaci变异。所有这些宿主标本都带有A.astaci基因型D组，单倍型d1，在邻国西班牙引起了大多数小龙虾鼠疫的爆发。相比之下,迄今为止，法国爆发的基因分型（包括本研究中最新分析的8次）主要是由基因型B组的菌株引起的，特定于信号小龙虾Pacifastacusleniusculus。在克氏疟原虫中发现的单倍型d1参与了其中一个新特征的爆发。我们的研究证实，克拉氏疟原虫是法国小龙虾鼠疫病原体的潜在重要水库，但不是螺旋藻大规模死亡率中病原体的主要来源，可能是由于不同生态要求的不同入侵宿主小龙虾。然而,随着Clarkii继续传播,该物种对本地小龙虾构成的威胁可能会增加。
