The oomycete Aphanomyces astaci is a pathogen emerging infectious disease affecting crayfish worldwide. Wherever it is, it leaves its deadly mark by being responsible for one of the most serious wildlife pandemics ever reported. It is among the 100 worst invasive alien species from all over the planet.
This pathogen originated in the southeastern United States, which is itself the largest center of diversity for crayfish species.
Until now, there were certain hypotheses about its origin in North America since it had caused outbreaks of plague in river crabs introduced from North America, such as the red crab, Procambarus clarkii, and the signal crab, Pacifastacus lenisuculus. The pathogen was also identified mainly in the same North American species.
A study carried out by an international team of scientists and directed by researchers from the Higher Council for Scientific Research (CSIC) in the Royal Botanical Garden (RJB) of CSIC, Laura Martin-Torrijos Y Javier Diéguez-Uribeondo, reveals that the pathogen is present in practically all the populations studied, and in at least 40% of the specimens analyzed.
The work, now published in the journal Scientific reports, confirms that the southeastern United States is the center of diversity for this pathogen after analyzing almost 400 crayfish from 30 localities in five states in the southeast of the country (South Carolina, Kansas , Kentucky, Louisiana and Mississippi). From this number of specimens, the pathogen was isolated in pure culture from 132 crabs.
“The rnnS and rnnL mitochondrial sequences indicate that the pathogen A. astaci from the southeastern United States exhibits the greatest genetic diversity described so far: 8 haplotypes, of the 12 known”, points out Javier Diéguez-Uribeondo.
The researcher adds that the findings that A. astaci is widely distributed and genetically diverse in that region show that “this pathogen originated in the southeastern United States, which is in turn the largest center of diversity for crab species. river. However, in contrast to the previous assumptions, the pathogen did not exhibit clear patterns of geographic distribution or specificity by crab species in this region ”.
A specialized pathogen in crayfish
This oomycete is a specialized pathogen in crayfish, a third of which are threatened with extinction on a global scale. The pathogen naturally coexists with North American crayfish, but can lethal colonize crayfish from other countries or continents, with almost no resistance.
Aphanomyces astaci has spread rapidly around the world through translocations of these chronically infected North American crabs.
Aphanomyces astaci has spread rapidly throughout the world through translocations of these North American crabs chronically infected with this pathogen. In river crayfish that are not native to this continent, plague infections generally cause death within a few days.
“Presumptions about the origin of the crayfish infestation were based on disease outbreaks that followed historical translocations of crayfish species from North America to many countries for use in the aquaculture, the sport fishing or the Commerce of aquarium specimens. The first outbreak of crayfish plague was registered in Europe in the 19th century, probably due to the introduction of the channel crab, Faxonius limosus ”, says Laura Martín-Torrijos, from the RJB-CSIC.
Starting in 1959, introductions on a large scale of another American species, the signal crab (Pacifastacus leniusculus). These introductions resulted in new outbreaks of plague that decimated native crayfish populations throughout Europe. The disease did not arrive in Spain until 1973 with the introduction of Red crab (Procambarus clarkii) and the signal crab, Pacifastacus leniusculus, began the drastic disappearance of the native species.
“Although the data demonstrate the North American origin of A. astaci, our knowledge of the crayfish plague pathogen in North America is still incipient,” acknowledges Martín-Torrijos and, therefore, “a clearer understanding of the diversity is needed. and distribution of A. astaci within its native range, not only to improve our understanding of the evolution and epidemiology of pandemic pathogens, but also to determine future management and research directions ”.
Fungi and pathogens that cause extinctions
During the last decades, mushrooms Y pathogens similar to these have caused several pandemics worldwide responsible for declining wildlife populations, even causing extinctions. They have had a particularly strong impact on freshwater ecosystems, causing a slope global in biodiversity of fresh water that is much greater than that observed in terrestrial ecosystems.
The Batrachochytrium dendrobatidis fungus originated in Asia and spread globally due to trade in amphibians, causing declines in more than 500 species of amphibians during the last half century. Additionally, fungal-like pathogens, such as Saprolegnia diclina and Saprolegnia ferax (Oomycetes), are also responsible for amphibian mass extinctions and can be spread by the fish trade. Another pathogenic oomycete, Aphanomyces invadans, causes epizootic ulcerative syndrome, which affects more than 100 species of fish in Asia, Australia, North America, and Africa.
Aphanomyces astaci, which naturally coexists with some North American crayfish species that are its chronic carriers, has caused massive mortality of freshwater crayfish species in Europe and Asia, and threatens other susceptible species in Madagascar, Oceania Y South America.
Laura Martín-Torrijos et al. “Tracing the origin of the crayfish plague pathogen, Aphanomyces astaci, to the Southeastern United States”. Scientific reports.
Rights: Creative Commons.