Search Results (11)

Freshwater amphipods of the genus Gammarus are important trophic components of aquatic ecosystems and are increasingly considered a potential bioresource for aquaculture. However, their role in the maintenance and transmission of infectious agents remains poorly understood. This study evaluated the presence of major crustacean and fish pathogens in Gammarus lacustris populations from Kazakhstan and characterized associated viral communities using metagenomic sequencing. Six pooled samples collected from freshwater ecosystems across Kazakhstan were screened using PCR and RT-PCR assays targeting World Organisation for Animal Health (WOAH)-listed pathogens, including White Spot Syndrome Virus, Taura Syndrome Virus, Infectious Myonecrosis Virus, Aphanomyces astaci, and Aphanomyces invadans. In parallel, high-throughput sequencing (Illumina NovaSeq) was performed to assess virome composition and structure. No WOAH-listed pathogens were detected, suggesting a low detectable occurrence of major notifiable agents under the conditions of the present study. Metagenomic analysis revealed a virome dominated by RNA viruses, particularly picorna-like viruses (Picornaviridae), Dicistroviridae, and Marnaviridae. Phylogenetic and genome organization analyses identified potentially novel or highly divergent viral lineages within Picornavirales. Collectively, these findings suggest a favorable epizootiological profile of G. lacustris populations while highlighting freshwater amphipods as hosts of diverse and partially uncharacterized viral communities relevant to aquatic disease surveillance and aquaculture biosecurity. Full article

This paper provides data on non-native fungus-like organisms (Oomycota, kingdom Stramenopila), their diversity, and distribution in Lithuania and is an addition to a previously published checklist of alien true fungi (Chytridiomycota, Ascomycota, and Basidiomycota; kingdom Fungi). All available published data were summarized, and the analysis showed that approximately 25% of recorded Lithuania stramenopilous fungus-like organism species are alien. The compiled list represented herein includes 54 species of alien terrestrial and aquatic stramenopilous fungus-like organisms (Oomycota). Most alien Oomycota are obligate pathogens of terrestrial plants. Aquatic organisms are represented by one alien dangerous crayfish pathogen, Aphanomyces astaci, which is currently noted as extinct in Lithuania. The taxonomy of the listed alien species of Oomycota has been revised, and the species names have been adjusted to reflect current nomenclature changes. The taxonomical and ecological analysis demonstrated the prevalence of terrestrial parasitic Peronosporales reported in Lithuania Oomycota and the highest diversity of alien species belonging to the Peronospora genus. The chronology of appearance, distribution within the country, and current status of these non-native organisms were assessed, and some of the most economically or ecologically important harmful invasive species were discussed. Full article

We adopted a morphometric approach to provide statistical support for the description of two different morphotypes (I, reproductive, II, non-reproductive) firstly observed in Procambarus clarkii specimens caught in a population from Sardinia Island (western Mediterranean). The morphometric study was preceded by molecular taxonomic identification using the mitochondrial Cytochrome C Oxidase subunit I (COI) gene. The presence or absence of the pathogen Aphanomyces astaci, responsible for the plague, was also investigated using the ribosomal Internal Transcribed Spacer (ITS) marker. The estimation of the size at onset of maturity (SOM) was further performed in males. Finally, the population structure was examined. Our results confirmed the entirety of the individuals as P. clarkii, and the absence of the pathogen A. astaci. Morphological analysis revealed a significant correlation between chela and carapace lengths, while intra- and inter-sexual dimorphism in the chela length confirmed the occurrence of the two morphotypes. The SOM in males was established between 35.0 and 37.1 mm carapace length. Finally, the size-population structure showed a Gaussian distribution. The recognition of the two distinct morphotypes in the crayfish could be useful as an additional tool not only to identify the reproductive period of this invasive crustacean but also to enrich the guidelines for the correct taxonomic identification of the species. Full article

Crayfish plague is a devastating disease of European freshwater crayfish and is caused by the oomycete Aphanomyces astaci (Ap. astaci), believed to have been introduced to Europe around 1860. All European species of freshwater crayfish are susceptible to the disease, including the white-clawed crayfish Austropotamobius pallipes. Ap. astaci is primarily spread by North American crayfish species and can also disperse rapidly through contaminated wet gear moved between water bodies. This spread, coupled with competition from non-indigenous crayfish, has drastically reduced and fragmented native crayfish populations across Europe. Remarkably, the island of Ireland remained free from the crayfish plague pathogen for over 100 years, providing a refuge for A. pallipes. However, this changed in 1987 when a mass mortality event was linked to the pathogen, marking its introduction to the region. Fortunately, crayfish plague was not detected again in Ireland until 2015 when a molecular analysis linked a mass mortality event in the Erne catchment to Ap. astaci. Since then, the pathogen has appeared across the island. Between 2015 and 2023, Ap. astaci was detected in 18 water catchments, revealing multiple genotypes. Intriguingly, the pathogen in Ireland is present without its natural host species. The uneven distribution of various genetic lineages strongly suggests the human-mediated transport of zoospores via contaminated water equipment as a primary cause of spread. This review details the timeline of these events, Ap. astaci’s introduction into Ireland, and its rapid spread. As well, this review references the genotypes that have been determined, and discusses the issue of non-indigenous crayfish species in Ireland and management efforts. Full article

In endangered crayfish conservation projects, it is paramount to map the distribution of the causative agent of crayfish plague, Aphanomyces astaci, in native populations. Considering the inapplicability of the destructive cuticular sampling protocol for monitoring endangered populations, we explored the use of non-invasive sampling techniques to detect this pathogen with molecular assays. In the present study, we exploited environmental DNA (testing increasing water volumes combined with different filter porosities) and cuticular swabs to collect A. astaci DNA. In addition, we evaluated the impact of the storage method on DNA preservation during field activities. After the first evaluations performed on both highly infected Austropotamobius pallipes and carrier Procambarus clarkii specimens in laboratory conditions, these sampling techniques were applied to wild populations of white-clawed crayfish. Our findings highlight better results with the filtration of 5 L of water with filters of 2.7 µm porosity for eDNA analysis and demonstrate that cuticular swabbing is equally effective as the World Organisation of Animal Health’s protocol. Storage in absolute ethanol proved to be the best solution to preserve swabs and filter samples for up to a week at room temperature. In conclusion, we suggest an integration of both sampling methods when monitoring A. astaci for conservation purposes. Full article

Crayfish plague, caused by the oomycete pathogen Aphanomyces astaci, is one of the most devastating of the emerging infectious diseases. This disease is responsible for the decline of native European and Asian freshwater crayfish populations. Over the last few decades, some European crayfish populations were reported to display partial to total resistance to the disease. The immune response in these cases was similar to that exhibited by the natural carriers of the pathogen, North American freshwater crayfish, e.g., weak-to-strong melanization of colonizing hyphae. We tested the degree of resistance displayed by 29 native Iberian populations of Austropotamobius pallipes that were challenged by zoospores of the pathogen. We measured the following parameters: (i) mean survival time, (ii) cumulative mortality, and (iii) immune response, and found that the total cumulative mortality of all the challenged populations was 100%. The integration of the results from these parameters did not allow us to find differences in resistance towards A. astaci among the northern and central populations of the Iberian Peninsula. However, in the southern populations, we could identify four distinct population responses based on an evaluation of a GLM analysis. In the first case, the similar response could be explained by the effect of a pathogen strain with a lower-than-expected virulence, and/or an actual increase in resistance. In the Southern populations, these differences appear to be the consequence of either whole population or individual resistance. Individuals that survived for a longer period than the others showed a stronger immune response, i.e., presence of partially or fully melanized hyphae, which is similar to that of North American crayfish species. This might be the consequence of different mechanisms of resistance or/and tolerance towards A. astaci. Full article

Oomycete pathogens in freshwaters, such as Saprolegnia parasitica and Aphanomyces astaci, are responsible for fish/crayfish population declines in the wild and disease outbreaks in aquaculture. Although the formation of infectious zoospores in the laboratory can be triggered by washing their mycelium with natural water samples, the physico-chemical properties of the water that might promote sporulation are still unexplored. We washed the mycelia of A. astaci and S. parasitica with a range of natural water samples and observed differences in sporulation efficiency. The results of Partial Least Squares Regression (PLS-R) multivariate analysis showed that SAC (spectral absorption coefficient measured at 254 nm), DOC (dissolved organic carbon), ammonium-N and fluoride had the strongest positive effect on sporulation of S. parasitica, while sporulation of A. astaci was not significantly correlated with any of the analyzed parameters. In agreement with this, the addition of environmentally relevant concentrations of humic acid, an important contributor to SAC and DOC, to the water induced sporulation of S. parasitica but not of A. astaci. Overall, our results point to the differences in ecological requirements of these pathogens, but also present a starting point for optimizing laboratory protocols for the induction of sporulation. Full article

Saprolegnia parasitica, the causative agent of saprolegniosis in fish, and Aphanomyces astaci, the causative agent of crayfish plague, are oomycete pathogens that cause economic losses in aquaculture. Since toxic chemicals are currently used to control them, we aimed to investigate their inhibition by essential oils of sage, rosemary, and bay laurel as environmentally acceptable alternatives. Gas Chromatography–Mass Spectrometry (GC–MS) analysis showed that the essential oils tested were rich in bioactive volatiles, mainly monoterpenes. Mycelium and zoospores of A. astaci were more sensitive compared to those of S. parasitica, where only sage essential oil completely inhibited mycelial growth. EC₅₀ values (i.e., concentrations of samples at which the growth was inhibited by 50%) for mycelial growth determined by the radial growth inhibition assay were 0.031–0.098 µL/mL for A. astaci and 0.040 µL/mL for S. parasitica. EC₅₀ values determined by the zoospore germination inhibition assay were 0.007–0.049 µL/mL for A. astaci and 0.012–0.063 µL/mL for S. parasitica. The observed inhibition, most pronounced for sage essential oil, could be partly due to dominant constituents of the essential oils, such as camphor, but more likely resulted from a synergistic effect of multiple compounds. Our results may serve as a basis for in vivo experiments and the development of environmentally friendly methods to control oomycete pathogens in aquaculture. Full article

The oomycete pathogen Aphanomyces astaci, also known as “crayfish plague”, is an obligate fungal-like parasite of freshwater crustaceans and is considered responsible for the ongoing decline of native European crayfish populations. A. astaci is thought to secrete a wide array of effectors and enzymes that facilitate infection, however their molecular mechanisms have been poorly characterized. Here, we report the identification of AA15 lytic polysaccharide monooxygenases (LPMOs) as a new group of secreted virulence factors in A. astaci. We show that this enzyme family has greatly expanded in A. astaci compared to all other oomycetes, and that it may facilitate infection through oxidative degradation of crystalline chitin, the most abundant polysaccharide found in the crustacean exoskeleton. These findings reveal new roles for LPMOs in animal–pathogen interactions, and could help inform future strategies for the protection of farmed and endangered species. Full article

Cherax destructor is a crayfish endemic to south-eastern Australia and one of the last alien crayfish to be introduced in Italy. In the Laghi di Ninfa Natural Reserve (Latium region, Central Italy), the species was probably introduced in 1999, but only reported for the first time in 2008. Nearby this area, the most widespread alien crayfish is the red swamp crayfish Procambarus clarkii. In the Natural Reserve, between 2008 and 2013 and during spring and summer, crayfish sampling was carried out with baited traps to assess the distribution of C. destructor and its possible relationship with P. clarkii. Cherax destructor was first recorded in 2008; few P. clarkii were detected in the cultivation ponds where C. destructor was present in 2012 and 2013. Moreover, crayfish plague analyses evidenced a positive result in two out of the 12 sampled P. clarkii. Cherax destructor is now completely absent from the Natural Reserve, while P. clarkii has spread in the area and was probably responsible for this eradication since C. destructor is vulnerable to crayfish plague which was also detected in the area. An ecosystem restoration project in the area favoured the spread of. P. clarkii; the implications of this intervention are discussed. Full article

This study aimed to evaluate the in vitro activity of Zanthoxylum rhoifolium bark (Zr-b) extracts against pathogenic aquatic oomycete/fungal isolates that cause different diseases in native European crayfish resulting in an elevated mortality rate and severe economic repercussions. n-hexane, chloroform, chloroform–methanol (9:1) and methanol extracts of Zr-b were used to evaluate the antifungal activity against the strain UEF88662 of Aphanomyces astaci (oomycete) and the strain SMM2 of Fusarium avenaceum (fungus). The anti-oomycete and antifungal activity was quantitatively evaluated by growth, survival and sporulation microbiological assays. The extracts tested demonstrated a dose-dependent inhibitory effect on oomycete and fungal growth and survival, as well as on the production of oomycete and fungal spores. This work presents alternatives for the treatment and prevention of the spreading of Aphanomyces astaci and Fusarium avenaceum, the etiological agents of the diseases crayfish plague and brown spot disease, respectively. The antifungal properties of Zanthoxylum rhoifolium bark extracts warrant further research on their use in the prevention and treatment of both oomycete and fungal diseases. The antifungal properties of Zanthoxylum rhoifolium bark extracts, shown in vitro, indicate the possibility of their use in new therapeutic and prophylactic strategies, providing perspectives for the design of in vivo studies. Full article