Self-limiting outbreak of crayfish plague in an Austropotamobius pallipes population of a river basin in the Abruzzi region (central Italy)

Abstract

Crayfish plague, caused by the oomycete Aphanomyces astaci, is a serious disease of European freshwater crayfish and has eliminated entire populations in several European countries. In September 2011, mortality was observed among the Austropotamobius pallipes population of a river basin in the Abruzzi region (central Italy), and A. astaci DNA was detected by PCR in dead crayfish. A systematic survey was carried out to evaluate the spread and the effects of the plague in the river basin. The source of the outbreak remained unknown since North American crayfish species, which frequently act as subclinical carriers of the infection, were not detected in the area. The A. pallipes population disappeared from a river stretch of ~1 km, where A. astaci infection was detected in dead crayfish. However, apparently unaffected crayfish were still present upstream of that area as well as in a tributary that joined the brook in the apparently depopulated stretch. A. astaci infection was not detected in dead individuals collected in the upstream area and tributary. A follow-up visit conducted in the following season showed the presence of A. pallipes in the river stretch hit by the plague. In this outbreak, the spread of the infection could have been limited by a low density of the crayfish population and by the geographic conformation of the river basin, which includes a dense network of small tributaries, characterized by high flow velocity and low water temperature. In this particular setting, crayfish plague outbreaks can remain undetected. This underlines the importance of active monitoring programs aimed at the prompt recognition of both episodes of mortality and the presence of non-indigenous crayfish species.

Monitoring of white-clawed crayfish (Austropotamobius pallipes) population during a crayfish plague outbreak followed by rescue

“…(i) It is known that crayfish density can act on the quantity of spore production during an outbreak (Caprioli et al, 2013). If so, we could expect more spore production in areas of high density and a quick spread of infection.…”

“…When plague occurs in a European crayfish population, the population is generally eliminated within short periods of time (Kozubíková et al, 2008;OIE, 2009) although a few cases of chronic infections have been recently reported for indigenous European crayfish species (Caprioli et al, 2013;Kušar et al, 2013;Viljamaa-Dirks et al, 2013). In some cases, the presence of a pond or dam may limit the upstream spread of disease (Kozubíková-Balcarova et al, 2014).…”

Flash‐flood potential: a proxy for crayfish habitat stability

“…Populations isolated due to fragmentation might have an advantage, being less susceptible to the expansion of invasive species and diseases (Caprioli et al, 2013;Kušar et al, 2013). For instance, two of the most representative invasive crayfish species in Europe, the spiny-cheek crayfish, Orconectes limosus (Rafinesque, 1817), and the red swamp crayfish, Procambarus clarkii (Girard, 1852), are adapted for lowland rivers (Holdich et al, 2006) and supposedly unable to colonize mountain streams (Petrusek et al, 2006).…”

Aphanomyces astaciPsI-genotype isolates from different Finnish signal crayfish stocks show variation in their virulence but still kill fast

“…In general, this disease has a bad reputation, but some A. astaci strains seem to show signs of avirulence (Jussila et al, 2011a;Makkonen, 2013). Certain strains of this parasite have likely adapted to their fairly recent European hosts, as the As-genotype is currently causing highly variable mortalities among native European crayfish both in laboratory experiments and among wild populations (Jussila et al, 2011Kokko et al, 2012;Svoboda et al, 2012;Caprioli et al, 2013;Kušar et al, 2013). So far, however, the evidence of virulence differences and potential evolution among PsI-genotype, or other more recently introduced A. astaci genotypes, has been lacking.…”