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Ulcerative dermal necrosis (UDN), a chronic skin condition, affects primarily mature wild salmonids returning from the sea to freshwater for their spawning. The involvement of water moulds such as Saprolegnia parasitica as a secondary pathogen in this disease is clear but the identification of a primary cause or of primary pathogen(s) remains elusive. In this opinion article, we re-visit UDN regarding epidemiology, pathology and aetiology and speculate the potential involvement of UV radiation in the initiation of UDN in salmonid fish returning from the sea. [ABSTRACT FROM AUTHOR]

Oomycetes are spore-forming eukaryotic microbes responsible for infections in animal and plant species worldwide, posing a threat to natural ecosystems, biodiversity and food security. Genomics and transcriptomics approaches, together with host interaction studies, give promising results towards better understanding of the infection mechanisms in oomycetes and their general biology. Significant development and progress in oomycetes genomic studies have been achieved over the past decades but further understanding of molecular processes, gene regulations and infection mechanisms are still needed. The use of molecular tools such as CRISPR/Cas and RNAi helped elucidate some of the molecular processes involved in host invasion and infection both in plant and animal pathogenic oomycetes. These methods provide an opportunity for accurate and detailed functional analysis involving various fields of studies such as genomics, epigenomics, proteomics, and interactomics. Functional gene characterisation is essential for filling the knowledge gaps in dynamic biological processes. However, every method has both advantages and limitations that should be considered before choosing the best method for investigating a particular research question. Here we review transformation systems, gene silencing and gene editing techniques in oomycetes, how they function, in which species and what are their main advantages and disadvantages. [ABSTRACT FROM AUTHOR]

Diseases caused by oomycete pathogens are a global threat to forestry, agriculture and aquaculture. Because of their complex life cycles, characterised by dormant resting structures that enable their survival for years under hostile environmental conditions, reducing the spread of oomycetes is a challenging task. In this review, we present an overview of this challenge, starting from the need to understand the natural and anthropogenic dispersal pathways of these pathogens. Focusing on the European Union, we explore current legislation that forms a backbone for biosecurity protocols against the spread of oomycetes through trade and transport. We discuss the options for prevention, containment and long-term management of oomycetes in different production settings, emphasising the importance of prevention as the most cost-efficient strategy to reduce the spread of these pathogens. Finally, we highlight some of the new and emerging technologies and strategies as potential tools in the integrated pest management of animal and plant diseases caused by oomycetes. We emphasise the urgency of actions to halt the global spread of these pathogens. [ABSTRACT FROM AUTHOR]

Research on the order Saprolegniales (Oomycota) has been an ongoing quest for more than a century. The best studied genera are Saprolegnia and Aphanomyces , known for their pathogenicity on freshwater animals. In this study, we reviewed 1073 papers and 2803 ITS sequences of Saprolegniales to investigate their taxonomy, diversity and potential roles in mainly freshwater ecosytems. We found that, in general, our knowledge on diversity and ecology of Saprolegniales is limited. Neither classic taxonomy nor available molecular techniques have been sufficient to delineate genera and species and show their relative distribution in freshwater-associated habitats. Also, we currently lack a comprehensive understanding of their involvement in carbon turnover and food web dynamics. Finally, due to lack of using high-throughput sequencing techniques, it is not clear how and to what extent communities of Saprolegniales might differ in freshwater econiches. Therefore, we provide a historical perspective on the establishment of Saprolegniales , explain improvements, highlight deficiencies, and finally propose new research avenues for more systematic studies. We conclude that challenges in studying Saprolegniales can be removed by increasing the practicality of classic taxonomy and applying available molecular toolboxes (multi-gene phylogeny and high-throughput sequencing). Additionally, inclusion of Saprolegniales in freshwater carbon cycling should be addressed for their better ecological resolution. • The real diversity and ecology of freshwater Saprolegniales is greatly unknown. • Multi-gene phylogeny should be able to resolve and delineate ambiguous taxa. • High-throughput sequencing will show any habitat-specificity in Saprolegniales. • Saprolegniales are involved in freshwater carbon cycling and food webs. [ABSTRACT FROM AUTHOR]

Aphanomyces invadans is a eukaryotic pathogen and the causative agent of Epizootic Ulcerative Syndrome (EUS) in fish and is responsible for mortalities of up to 100% in aquaculture. A. invadans was first discovered in Japan in 1971, and since then it has been found in Australia, North America, Southern African countries and Asia. Methods for the correct identification of A. invadans are well established now and involve PCR-based detection and microscopy. However, the pathogenesis of A. invadans is poorly understood. Environmental stress (mainly temperature) and the associated immunocompromised fish seem to induce infections of A. invadans and outbreaks of EUS. Understanding the process of infection in more depth is fundamental for the discovery of novel effective treatments to combat the disease. In this review, we discuss morphological characteristics of A. invadans and its pathogenicity as well as various approaches of treatment. [ABSTRACT FROM AUTHOR]

Oomycetes form a phylogenetically distinct group of eukaryotic microorganisms that include some of the most notorious pathogens of plants and animals. Through the deployment of a remarkably diverse array of effector proteins, oomycete pathogens succeed to overcome host defences and cause infection. Effectors can operate extracellularly or enter living cells where they target diverse subcellular compartments. Genome sequence information indicates that oomycetes express several hundred host-translocating effectors potentially targeting a myriad of host processes. To counteract, plants rely on a wide variety of extra- and intracellular immune receptors facilitating pattern-triggered and effector-triggered immunity, respectively. Similarly, effectors from animal pathogenic oomycetes also target host immune response pathways, which in turn causes the activation of the humoral and adaptive immune system. In this review, we compare plant and animal pathogenic oomycete effectors regarding their type, function, genetic diversity, as well as host responses. [ABSTRACT FROM AUTHOR]

Abstract: A very large number of diseases in agriculture and aquaculture are caused by fungal-like micro-organisms, classified as Oomycetes or water moulds. Collectively, oomycetes represent a huge threat to global food security. In addition, several oomycetes can cause environmental disasters, by wiping out native species of trees, crustacians and amphibians. The group representing the aquatic oomycetes are relatively understudied in contrast to their terrestrial counterparts that predominantly infect plants (e.g. Phytophthora, Pythium and Bremia spp.). This review focuses on the unique characteristics of two aquatic Oomycetes, Saprolegnia parasitica and Saprolegnia diclina with respect to their impact on aquaculture, animal health and the surrounding environment. The species characteristics, ecology, biology, infectivity and identification methods are described and the latest research insights are discussed. [Copyright &y& Elsevier]

Abstract: The most notorious oomycetes, such as Phytophthora infestans, are pathogens of higher plants, although numerous other species of these fungal-like microorganisms infect algae, crustacea, nematodes, fish and mammals. While there is now ample evidence that oomycetes and fungi deliver effector proteins inside the host cell during infection, like bacteria using the well characterised type III secretion system, the mechanism employed by eukaryotic pathogens remains unclear. In oomycetes this process depends on an N-terminal motif defined by a short conserved amino acid sequence (RxLR) located near the signal peptide of many secreted proteins. This motif resembles the host-cell targeting signal found in virulence proteins from the malaria parasite Plasmodium falciparum (RxLxE/D/Q). This review will focus on the recent findings contributing to the understanding of the delivery of oomycete effector molecules into the host cells, with emphasis on how they compare with various models proposed for filamentous fungi and the malaria parasite. [ABSTRACT FROM AUTHOR]

Abstract: Oomycetes cause destructive diseases on both animals and plants. The epidemic spread of oomycete diseases is primarily based on rapid dispersal from host to host by free swimming zoospores. These single-nucleated spores are formed in sporangia and are only released in aqueous environments. Oomycetes are classified in the Kingdom of the Stramenopiles or Chromista, which is comprised of several organisms, including the golden brown algae. The unique shared attribute found in most Stramenopiles is the morphology of the zoospores and especially the structure of their two flagella. They have one tinsel flagellum, and one whiplash flagellum. Only the tinsel flagellum has distinctive flagellar hairs. Zoospore formation can occur within minutes and it is considered one of the fastest developmental processes in any biological system. Once released from the sporangium they are able to exhibit chemotactic responses, electrotaxis, and autotaxis or autoaggregation to target new hosts for infection. Here we discuss the latest discoveries in the development and biology of the oomycete zoospore. [Copyright &y& Elsevier]