Demetra Andreou

Identification of a rosette-like agent as Sphaerothecum destruens, a multi-host fish pathogen.

A recent threat to European fish diversity was attributed to an infectious pathogen, a rosette-like intracellular parasite carried by invasive cyprinids. Here we show that the emerging rosette-like agent is Sphaerothecum destruens, originally found to be responsible for disease outbreaks in salmon in the United States. Sequencing of the ribosomal internal transcribed spacer (ITS) DNA highlights some level of geographical isolation. Unlike the situation in the United States, its occurrence in invasive fishes presents a risk of spread from wild invasive populations to sympatric populations of susceptible native fish and as such represents a risk for fisheries, as movement of fish for stocking purposes is common practice.

Introduced Pathogens and Native Freshwater Biodiversity: A Case Study of Sphaerothecum destruens

A recent threat to European fish diversity was attributed to the association between an intracellular parasite, Sphaerothecum destruens, and a healthy freshwater fish carrier, the invasive Pseudorasbora parva originating from China. The pathogen was found to be responsible for the decline and local extinction of the European endangered cyprinid Leucaspius delineatus and high mortalities in stocks of Chinook and Atlantic salmon in the USA. Here, we show that the emerging S. destruens is also a threat to a wider range of freshwater fish than originally suspected such as bream, common carp, and roach. This is a true generalist as an analysis of susceptible hosts shows that S. destruens is not limited to a phylogenetically narrow host spectrum. This disease agent is a threat to fish biodiversity as it can amplify within multiple hosts and cause high mortalities.

Current ecological understanding of fungal-like pathogens of fish: what lies beneath?

Despite increasingly sophisticated microbiological techniques, and long after the first discovery of microbes, basic knowledge is still lacking to fully appreciate the ecological importance of microbial parasites in fish. This is likely due to the nature of their habitats as many species of fish suffer from living beneath turbid water away from easy recording. However, fishes represent key ecosystem services for millions of people around the world and the absence of a functional ecological understanding of viruses, prokaryotes, and small eukaryotes in the maintenance of fish populations and of their diversity represents an inherent barrier to aquatic conservation and food security. Among recent emerging infectious diseases responsible for severe population declines in plant and animal taxa, fungal and fungal-like microbes have emerged as significant contributors. Here, we review the current knowledge gaps of fungal and fungal-like parasites and pathogens in fish and put them into an ecological perspective with direct implications for the monitoring of fungal fish pathogens in the wild, their phylogeography as well as their associated ecological impact on fish populations. With increasing fish movement around the world for farming, releases into the wild for sport fishing and human-driven habitat changes, it is expected, along with improved environmental monitoring of fungal and fungal-like infections, that the full extent of the impact of these pathogens on wild fish populations will soon emerge as a major threat to freshwater biodiversity.

Understanding the threats posed by non-native species: public vs. conservation managers.

Public perception is a key factor influencing current conservation policy. Therefore, it is important to determine the influence of the public, end-users and scientists on the prioritisation of conservation issues and the direct implications for policy makers. Here, we assessed public attitudes and the perception of conservation managers to five non-native species in the UK, with these supplemented by those of an ecosystem user, freshwater anglers. We found that threat perception was not influenced by the volume of scientific research or by the actual threats posed by the specific non-native species. Media interest also reflected public perception and vice versa. Anglers were most concerned with perceived threats to their recreational activities but their concerns did not correspond to the greatest demonstrated ecological threat. The perception of conservation managers was an amalgamation of public and angler opinions but was mismatched to quantified ecological risks of the species. As this suggests that invasive species management in the UK is vulnerable to a knowledge gap, researchers must consider the intrinsic characteristics of their study species to determine whether raising public perception will be effective. The case study of the topmouth gudgeon Pseudorasbora parva reveals that media pressure and political debate has greater capacity to ignite policy changes and impact studies on non-native species than scientific evidence alone.

Sphaerothecum destruens pathology in cyprinids

Sphaerothecum destruens is a significant intracellular parasite of fish which has caused disease and mortalities in cultured north American Chinook salmon Oncorhynchus tshawytscha and Atlantic salmon Salmo salar. Several hosts for S. destruens have been identified within the Salmonidae family, and the histopathology of the infection can differ between hosts. Recently, S. destruens has been associated with the most invasive cyprinid species in Europe, topmouth gudgeon Pseudorasbora parva. Accurate disease identification based on thorough descriptions of clinical signs and histopathology in this new range of hosts is thus paramount to support further epizootiological studies. In this study, the associated histopathology of S. destruens infection is described along with its pathogenesis in the endangered cyprinid sunbleak Leucaspius delineatus. Histological examination of 100 L. delineatus in a wild population in the south of England revealed the presence of S. destruens infections, with a prevalence of 5% with S. destruens, suggesting an over-dispersed distribution within the L. delineatus sample. Clinical signs of the infection were absent, but histological examination revealed the presence of both disseminated and nodular lesions in several organs.

Temperature Influence on Production and Longevity of Sphaerothecum destruens Zoospores

Abstract The majority of pathogens that cause high host mortalities are capable of infecting more than 1 host species. One characteristic of pathogens, which enables infection of multiple hosts, is the existence of free-living infectious stages, e.g., zoospores that are produced in vast numbers. Understanding the influence of environmental factors, particularly temperature, on the production and survival of these free-living stages is key to predicting future spread and emergence of disease. The rosette agent, Sphaerothecum destruens, is a significant multi-host intracellular fish parasite, with an obligate intracellular spore stage and a free-living (extracellular), potentially infectious, zoospore stage. It has caused high mortalities in endangered and commercially important fish species. Here we investigate the influence of temperature on S. destruens zoospore production and longevity. Our results indicate a wide temperature tolerance of the spore and zooflagellate stage with later onset and longer lifespan of zoospores at lower temperatures. This has important implications for the environmental persistence of S. destruens and provides additional information on the pathogens life cycle with direct implications for S. destruens risk assessment.

First Detection of Mycobacterium ulcerans DNA in Environmental Samples from South America

The occurrences of many environmentally-persistent and zoonotic infections are driven by ecosystem changes, which in turn are underpinned by land-use modifications that alter the governance of pathogen, biodiversity and human interactions. Our current understanding of these ecological changes on disease emergence however remains limited. Buruli ulcer is an emerging human skin disease caused by the mycobacterium, Mycobacterium ulcerans, for which the exact route of infection remains unclear. It can have a devastating impact on its human host, causing extensive necrosis of the skin and underlying tissue, often leading to permanent disability. The mycobacterium is associated with tropical aquatic environments and incidences of the disease are significantly higher on floodplains and where there is an increase of human aquatic activities. Although the disease has been previously diagnosed in South America, until now the presence of M. ulcerans DNA in the wild has only been identified in Australia where there have been significant outbreaks and in western and central regions of Africa where the disease is persistent. Here for the first time, we have identified the presence of the aetiological agents DNA in environmental samples from South America. The DNA was positively identified using Real-time Polymerase Chain Reaction (PCR) on 163 environmental samples, taken from 23 freshwater bodies in French Guiana (Southern America), using primers for both IS2404 and for the ketoreductase-B domain of the M. ulcerans mycolactone polyketide synthase genes (KR). Five samples out of 163 were positive for both primers from three different water bodies. A further nine sites had low levels of IS2404 close to a standard CT of 35 and could potentially harbour M. ulcerans. The majority of our positive samples (8/14) came from filtered water. These results also reveal the Sinnamary River as a potential source of infection to humans.

Complex temporal climate signals drive the emergence of human water-borne disease

Predominantly occurring in developing parts of the world, Buruli ulcer is a severely disabling mycobacterium infection which often leads to extensive necrosis of the skin. While the exact route of transmission remains uncertain, like many tropical diseases, associations with climate have been previously observed and could help identify the causative agents ecological niche. In this paper, links between changes in rainfall and outbreaks of Buruli ulcer in French Guiana, an ultraperipheral European territory in the northeast of South America, were identified using a combination of statistical tests based on singular spectrum analysis, empirical mode decomposition and cross-wavelet coherence analysis. From this, it was possible to postulate for the first time that outbreaks of Buruli ulcer can be triggered by combinations of rainfall patterns occurring on a long (i.e., several years) and short (i.e., seasonal) temporal scale, in addition to stochastic events driven by the El Niño-Southern Oscillation that may disrupt or interact with these patterns. Long-term forecasting of rainfall trends further suggests the possibility of an upcoming outbreak of Buruli ulcer in French Guiana.

Isolation and culture of Sphaerothecum destruens from Sunbleak (Leucaspius delineatus) in the UK and pathogenicity experiments in Atlantic salmon (Salmo salar).

The sunbleak (Leucaspius delineatus), a cyprinid fish native to continental Europe and now established in the UK, is experiencing population decline which appears to be linked to the spread of the invasive Asian cyprinid (Pseudorasbora parva). A population of sunbleak in the UK has previously been identified as infected with S. destruens at low prevalence. Because Sphaerothaecum destruens has, on occasion, caused severe disease in cultured and wild salmonids the aim of this work was to establish laboratory cultures of S. destruens from sunbleak in the UK and use these cultures in challenge experiments to determine if the UK isolate of S. destruens from cyprinid species is a potential threat to Atlantic salmon (Salmo salar). The first isolation and culture of S. destruens in the UK and from a cyprinid species is described. Cultured S. destruens spores from sunbleak are infective to EPC, CHSE and FHM cells, replicating most rapidly in FHM and EPC cells. Spores can be induced to zoosporulate in water forming motile, uni-flagellated zoospores. Challenge experiments indicated the spores are able to replicate and disperse in Atlantic salmon and are associated with increased mortality (up to 90%) when injected intraperitonealy.

Individual genetic tagging for teleosts: an empirical validation and a guideline for ecologists.

The efficiency of individual genetic tagging was determined by using passive integrated transponders (PIT) as a comparative conventional tagging method. Fifty-five common dace Leuciscus leuciscus were captured in the wild, PIT tagged and fin clipped (for DNA analysis). Thirty fish were recaptured on three occasions and tissue samples were collected. Using 18 microsatellite loci, 79-94% of the recaptures were correctly assigned. Experience with scoring L. leuciscus microsatellites led to more individuals correctly assigned. Allowing matches that differed by one or two alleles resulted in 100% of all recaptures successfully assigned irrespective of the observer. Reducing the set of loci to five to six loci appropriately selected did not affect the assignment rate, demonstrating that costs can be subsequently reduced. Despite their potential benefits, the application of genetic tags for teleosts has been limited. Here, it was demonstrated that genetic tagging could be applied, and a clear guideline (flowchart) is provided on how this method can be developed for teleosts and other organisms, with subsequent practical applications to ecology, evolutionary biology and conservation management.