Abstract
The oomycete Aphanomyces astaci is an emerging infectious pathogen affecting freshwater crayfish worldwide and is responsible for one of the most severe wildlife pandemics ever reported. The pathogen has caused mass mortalities of freshwater crayfish species in Europe and Asia, and threatens other susceptible species in Madagascar, Oceania and South America. The pathogen naturally coexists with some North American crayfish species that are its chronic carriers. Presumptions that A. astaci originated in North America are based on disease outbreaks that followed translocations of North American crayfish and on the identification of the pathogen mainly in Europe. We studied A. astaci in the southeastern US, a center of freshwater crayfish diversity. In order to decipher the origin of the pathogen, we investigated (1) the distribution and haplotype diversity of A. astaci, and (2) whether there are crayfish species-specificities and/or geographical restrictions for A. astaci haplotypes. A total of 132 individuals, corresponding to 19 crayfish species and one shrimp species from 23 locations, tested positive for A. astaci. Mitochondrial rnnS and rnnL sequences indicated that A. astaci from the southeastern US exhibited the highest genetic diversity so far described for the pathogen (eight haplotypes, six of which we newly describe). Our findings that A. astaci is widely distributed and genetically diverse in the region supports the hypothesis that the pathogen originated in the southeastern US. In contrast to previous assumptions, however, the pathogen exhibited no clear species-specificity or geographical patterns.
Highlights
During the past few decades, fungal and fungal-like pathogens have caused several worldwide pandemics responsible for declines in wildlife populations—even causing e xtinctions[1,2,3,4,5]
We report and describe for the first time the presence, distribution and genetic diversity of the crayfish plague pathogen, A. astaci, in its potential center of origin, the southeastern U S68
Only two haplotypes had been found in the five North American crayfish species examined from California, Michigan and Pennsylvania (Pacifastacus leniusculus, Cambarus bartonii, Faxonius obscurus, Faxonius rusticus and Faxonius virilis)[62,63,64]
Summary
During the past few decades, fungal and fungal-like pathogens have caused several worldwide pandemics responsible for declines in wildlife populations—even causing e xtinctions[1,2,3,4,5] Globalization facilitates these pandemics—usually consequences of the transport and introduction of exotic and invasive species[6,7,8]. Fungal-like pathogens, such as Saprolegnia diclina and Saprolegnia ferax (Oomycetes), are responsible for mass extinctions in a mphibians[20,21] and may be spread by the fish trade[22] Another pathogenic oomycete, Aphanomyces invadans, causes epizootic ulcerative syndrome (EUS), affecting more than 100 fish species in Asia, Australia, North America and A frica[23,24]. Only three studies have confirmed the presence of the pathogen in North America, revealing only two of the previously described haplotypes: a and b-haplotypes[62,63,64]
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