Tracing the origin of the crayfish plague pathogen, Aphanomyces astaci, to the Southeastern United States

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.

First Detection of the Crayfish Plague Pathogen Aphanomyces astaci in Costa Rica: European Mistakes Should Not Be Repeated

“…We also determined that the A. astaci found in this P. clarkii population belongs to the D-haplogroup. Four haplotypes have been identified for A. astaci in P. clarkii: d1, d2, d3, and usa6 (Makkonen et al, 2018;Martín-Torrijos et al, 2018, 2021b. The four mitochondrial rnnS sequences obtained in this study are all identical to those corresponding to either the d1 or d2 rnnS haplotypes reported by Makkonen et al (2018).…”

“…In Costa Rica, although there are no native crayfish species, there are approximately 26 native species of freshwater decapods (21 shrimp species belonging to the families Atyidae and Palaemonidae, and 15 crab species belonging to Pseudothelphusidae) (Lara and Wehrtmann, 2011;Lara et al, 2013;Magalhães et al, 2015). Despite the seemingly narrow host range of A. astaci (Unestam, 1972;Diéguez-Uribeondo et al, 2009), several studies have shown transmission of the pathogen to other freshwater decapods including Atya gabonensis, Atyopsis moluccensis, Eriocheir sinensis, Macrobrachium dayanum, Macrobrachium lanchesteri, Neocaridina davidi, Palaemon kadiakensis, and Potamon potamios (Schrimpf et al, 2014;Svoboda et al, 2014;Putra et al, 2018;Mrugała et al, 2019;Martín-Torrijos et al, 2021b). Although the coexistence of native freshwater decapods with P. clarkii has not been reported yet in Costa Rica, the potential impact of the invasive species presence on freshwater fauna in the country should be evaluated.…”

“…The aquaria were maintained at 25 • C, and crayfishes were checked daily for the presence of molts. Molts were maintained in sterile distilled water for 3 days prior to their examination under a microscope to detect for the presence of A. astaci, as described in Martín-Torrijos et al (2021b). Finally, molts were individually preserved in 96% ethanol for further examination and the molecular analyses.…”

Real-Time PCR Assays for Rapid Identification of Common Aphanomyces astaci Genotypes

“…Molecular typing by the random amplified polymorphic DNA (RAPD) of A. astaci axenic laboratory cultures (Huang et al, 1994) has allowed the identification of five distinct genotype groups, labeled alphabetically from A to E (reviewed in Rezinciuc et al, 2015). The application of genotyping markers to clinical samples (i.e., DNA isolates from infected crayfish), particularly the analysis of microsatellite loci (Grandjean et al, 2014) and sequencing of mitochondrial ribosomal genes (Makkonen et al, 2018), allowed the discovery of additional variation among A. astaci strains, both in outbreaks of the disease (Grandjean et al, 2014;Martín-Torrijos et al, 2018) and from non-symptomatic hosts (Mrugała et al, 2017a;Martín-Torrijos et al, 2018;Panteleit et al, 2019;Martín-Torrijos et al, 2021). However, the vast majority of crayfish plague outbreaks in Europe analyzed so far have been linked to one of the four RAPD-defined genotype groups either isolated from one of the widespread crayfish invaders (groups B, D, E; Huang et al, 1994;Diéguez-Uribeondo et al, 1995;Kozubíková et al, 2011b) or associated with historical mortalities (group A; Huang et al, 1994).…”

“…In particular, causative agents of crayfish plague outbreaks have been genotyped in regions where crayfish plague is considered a major threat to indigenous crayfish conservation, and thus research has been intensive in the past two decades. It is important to keep in mind that the diversity of A. astaci in its native range is largely unexplored, and substantial additional variation has been already discovered since this oomycete became studied in other natural hosts (Panteleit et al, 2019;Martín-Torrijos et al, 2021).…”