Proliferative Kidney Disease Research Articles

Ecological Implications of the Detection of Freshwater Bryozoan Cristatella mucedo (Bryozoa: Phylactolaemata) and Myxozoan Parasite Tetracapsuloides bryosalmonae (Cnidaria: Malacosporea) in Southwest Montana

Ecological Implications of the Detection of Freshwater Bryozoan Cristatella mucedo (Bryozoa: Phylactolaemata) and Myxozoan Parasite Tetracapsuloides bryosalmonae (Cnidaria: Malacosporea) in Southwest Montana

Thermotactic behaviour in lacustrine and riverine forms of Salmo trutta and its relevance to an emerging parasitic disease (PKD) in the wake of climate change

The thermotactic response of brown trout (Salmo trutta) was examined with the goal to investigate potential effects of the emerging temperature-dependent fatal trout disease PKD (proliferative kidney disease). First the differences in cold-water preferences of two forms of brown trout, lacustrine (migratory) and riverine, were determined. Second, it was studied whether this preference was changed in fish infected with PKD. The experiment involved a one-week habituation period at 14 °C in a two-chamber runway followed by a week of 3 °C temperature difference between the two runways. The fish could freely move between lanes via an opening at the end where food was provided. The temperature manipulation was repeated twice, and there were 3 trials per experimental group. All fish developed a clear spatial preference in the test. Lacustrine trout demonstrated a preference for warmer water, while riverine trout preferred cooler water. This may increase the risk to PKD in the lacustrine form. Most strikingly, riverine trout experimentally exposed to Tetracapsuloides bryosalmonae, the parasite that causes PKD, demonstrated stronger cold-seeking behaviour than control fish. Cold seeking behaviour suggests the occurrence of a disease-induced behavioural chill response, which may play an important role in disease recovery. This demonstrates the significance of protecting river connectivity and cold-water sanctuaries as management strategies for preserving salmonid populations in a warming climate.

The myxozoans Myxobolus cerebralis and Tetracapsuloides bryosalmonae modulate rainbow trout immune responses: quantitative shotgun proteomics at the portals of entry after single and co-infections.

Little is known about the proteomic changes at the portals of entry in rainbow trout after infection with the myxozoan parasites, Myxobolus cerebralis, and Tetracapsuloides bryosalmonae. Whirling disease (WD) is a severe disease of salmonids, caused by the myxosporean M. cerebralis, while, proliferative kidney disease (PKD) is caused by T. bryosalmonae, which instead belongs to the class Malacosporea. Climate change is providing more suitable conditions for myxozoan parasites lifecycle, posing a high risk to salmonid aquaculture and contributing to the decline of wild trout populations in North America and Europe. Therefore, the aim of this study was to provide the first proteomic profiles of the host in the search for evasion strategies during single and coinfection with M. cerebralis and T. bryosalmonae. One group of fish was initially infected with M. cerebralis and another group with T. bryosalmonae. After 30 days, half of the fish in each group were co-infected with the other parasite. Using a quantitative proteomic approach, we investigated proteomic changes in the caudal fins and gills of rainbow trout before and after co-infection. In the caudal fins, 16 proteins were differentially regulated post exposure to M. cerebralis, whereas 27 proteins were differentially modulated in the gills of the infected rainbow trout post exposure to T. bryosalmonae. After co-infection, 4 proteins involved in parasite recognition and the regulation of host immune responses were differentially modulated between the groups in the caudal fin. In the gills, 11 proteins involved in parasite recognition and host immunity, including 4 myxozoan proteins predicted to be virulence factors, were differentially modulated. The results of this study increase our knowledge on rainbow trout co-infections by myxozoan parasites and rainbow trout immune responses against myxozoans at the portals of entry, supporting a better understanding of these host-parasite interactions.

Optimal detection protocol of Tetracapsuloides bryosalmonae by environmental DNA: A comparison of qPCR and ddPCR approaches

AbstractInvestigation of environmental DNA (eDNA) is increasingly used to precisely and non‐invasively detect and monitor pathogens. Among these, Tetracapsuloides bryosalmonae is a myxozoan endoparasite that causes proliferative kidney disease (PKD) in salmonid fish. Although the detection of T. bryosalmonae DNA in water samples has been shown to be promising and successful, method comparison and cross‐validation are currently lacking. This study aims to directly compare the sensitivity of different eDNA‐based methods in field and laboratory applications, and to develop an easy‐to‐apply and sensitive protocol to monitor T. bryosalmonae occurrence non‐invasively by its eDNA in water samples. First, we tested three existing probe‐based T. bryosalmonae‐specific detection assays in parallel by comparing the limit of detection (LOD) and limit of quantification (LOQ) using quantitative PCR (qPCR) and digital droplet PCR (ddPCR) platforms. Second, the impact of different filter types and water volumes on the detection probability was tested by sampling water directly from riverbanks with a syringe‐based protocol. The most sensitive detection protocol was the combination of the probe‐based assay published by Bettge et al. run via ddPCR, resulting in a LOD of 1.65 copies/μL input (6.6 copies/reaction) and a LOQ of 3.66 copies/μL input (14.67 copies/reaction). The type of filter (Sterivex™ compared to Millex®) did not significantly influence detection probability, however, the volume of water sampled (600 mL compared to 300 mL) significantly affected the probability of capturing eDNA in a sample. Based on modeled probabilities of eDNA capture and detection, we calculated that using the Bettge et al. assay via the ddPCR platform for data collection, 95% overall detection probability could be achieved with three replicates of 600 mL filtered water with Sterivex™ filters. Based on this cross‐validation of assays and detection platforms, we provide a cost‐effective, straightforward, and highly sensitive laboratory analysis workflow to detect DNA of T. bryosalmonae from water samples.

WITHDRAWN: Molecular identification of myxozoans and helminths in the black goby Gobius niger L. (Gobiiformes: Gobiidae) from the Finnish Archipelago, Baltic sea

Black gobies (Gobius niger) from the Finnish Archipelago, Baltic Sea, were screened for helminth and myxozoan infections in summer 2020. Helminths were identified morphologically and/or molecularly, myxozoan DNA was only detected during molecular screening. Altogether 30 novel sequences were generated and analysed using maximum likelihood estimation. Morphological and phylogenetic analyses based on SSU rDNA (myxozoans) and mitochondrial genes (helminths) revealed the presence of 10 species: two species of Myxozoa (a putative new species of Myxobolus and Tetracapsuloides bryosalmonae), and eight helminth species belonging to the Digenea (Diplostomum mergi Lineage 3), Cestoda (Bothriocephalus scorpii), Nematoda (Contracaecum rudolphii A, Cucullanus sp. and Hysterothylacium aduncum), and Acanthocephala (a putative new species of Corynosoma, Corynosoma semerme and Neoechinorhynchus sp.). Phylogenetic and comparative sequence analyses revealed that the putative new acanthocephalan species is closely related to C. neostrumosum in the Caspian Sea. Myxobolus sp. was resolved as closely related but distinct from a species described from freshwater fish in Lake Balaton, Hungary. In addition to these two putative new species, the black goby represents a new host record for four parasite species (Tetracapsuloides bryosalmonae, Diplostomum mergi Lineage 3, Contracaecum rudolphii A and Corynosoma semerme). The Finnish Archipelago is a novel locality record for four species (Myxobolus sp., Corynosoma sp., Diplostomum mergi Lineage 3 and Bothriocephalus scorpii).

The Role of Monocyte Chemoattractant Protein-1 (MCP-1) in Diabetic Kidney Disease

Monocyte chemoattractant protein-1 plays an important role in kidney disease. In several studies, the role of MCP-1 as a urine biomarker has been extensively studied. In many kidney diseases, there are elevated levels of MCP-1 in the kidney tissue and this is an important cause of monocyte infiltration in the pathogenesis of kidney damage. Elevated urinary MCP-1 levels have been able to predict outcome in proliferative kidney diseases such as lupus nephritis. However, in several studies it was also found that there was an increase in MCP-1 in diabetic kidney disease. Macrophages have even appeared early in diabetic kidney disease and are associated with the progression of kidney disease. Urinary MCP-1 levels are related to the degree of leukocyte infiltration in the tubulointerstitial. This supports inflammatory factors as part of the pathogenesis of diabetic kidney disease.

Investigation of Proliferative Kidney Disease in Brown Trout and Habitat Characteristics Associated with a Swiss Wastewater Treatment Plant

Wastewater treatment plants (WWTP) play a critical role in mitigating adverse environmental impacts of urban and industrial wastewater by removing pollutants and reducing the risk of contamination. Discharges of treated effluents from WWTPs can still have significant effects on freshwater ecosystems, particularly on sensitive species like brown trout. We analyzed the effects of a modern WWTP on a freshwater ecosystem, studying fish biodiversity and biomass, the occurrence of the parasitic disease Proliferative Kidney Disease (PKD) on brown trout, river water temperatures throughout the year and fish habitat and diversity. No major differences between up- and downstream of the WWTP were observed in habitat structure and attractiveness, fish biomass and species diversity, nor in PKD prevalence or intermediate host presence. However, immediately at the WWTP’s effluent and continuing downstream, the water temperature rose by almost 1 °C. While WWTPs are crucial for reducing the environmental impact of urban and industrial wastewater, their effluents can still have important consequences for freshwater ecosystems. Brown trout are particularly susceptible to increases in water temperature, especially regarding PKD severity and consequent mortality. To ensure the long-term health and sustainability of freshwater ecosystems, it is imperative to improve measures to minimize water temperature rises and mitigate downstream cascade effects on sensitive organisms like brown trout.

Spatial and intra-host distribution of myxozoan parasite Tetracapsuloides bryosalmonae among Baltic sea trout (Salmo trutta).

Proliferative kidney disease caused by the myxozoan parasite Tetracapsuloides bryosalmonae has been actively studied in juvenile salmonids for decades. However, very little is known about parasite prevalence and its geographical and intra-host distribution at older life stages. We screened T. bryosalmonae among adult sea trout (Salmo trutta) (n = 295) collected along the Estonian Baltic Sea coastline together with juvenile trout from 33 coastal rivers (n = 1752) to assess spatial infection patterns of the adult and juvenile fish. The parasite was detected among 38.6% of adult sea trout with the prevalence increasing from west to east, and south to north, along the coastline. A similar pattern was observed in juvenile trout. Infected sea trout were also older than uninfected fish and the parasite was detected in sea trout up to the age of 6 years. Analysis of intra-host distribution of the parasite and strontium to calcium ratios from the otoliths revealed that (re)infection through freshwater migration may occur among adult sea trout. The results of this study indicate that T. bryosalmonae can persist in a brackish water environment for several years and that returning sea trout spawners most likely contribute to the parasite life cycle by transmitting infective spores.

Differentially expressed transcripts of Tetracapsuloides bryosalmonae (Cnidaria) between carrier and dead-end hosts involved in key biological processes: novel insights from a coupled approach of FACS and RNA sequencing

Tetracapsuloides bryosalmonae is a malacosporean endoparasite that infects a wide range of salmonids and causes proliferative kidney disease (PKD). Brown trout serves as a carrier host whereas rainbow trout represents a dead-end host. We thus asked if the parasite adapts to the different hosts by changing molecular mechanisms. We used fluorescent activated cell sorting (FACS) to isolate parasites from the kidney of brown trout and rainbow trout following experimental infection with T. bryosalmonae. The sorted parasite cells were then subjected to RNA sequencing. By this approach, we identified 1120 parasite transcripts that were expressed differentially in parasites derived from brown trout and rainbow trout. We found elevated levels of transcripts related to cytoskeleton organisation, cell polarity, peptidyl-serine phosphorylation in parasites sorted from brown trout. In contrast, transcripts related to translation, ribonucleoprotein complex biogenesis and subunit organisation, non-membrane bounded organelle assembly, regulation of protein catabolic process and protein refolding were upregulated in rainbow trout-derived parasites. These findings show distinct molecular adaptations of parasites, which may underlie their distinct outcomes in the two hosts. Moreover, the identification of these differentially expressed transcripts may enable the identification of novel drug targets that may be exploited as treatment against T. bryosalmonae. We here also describe for the first time how FACS based isolation of T. bryosalmonae cells from infected kidney of fish fosters research and allows to define differentially expressed parasite transcripts in carrier and dead-end fish hosts.

Does treatment of brown trout with the parasite causing PKD increase stocking success and boost resilience against the disease?

AbstractIn Salmonidae, infections with the parasite Tetracapsuloides bryosalmonae may lead to a temperature‐dependent proliferative disease of the kidney (PKD). Trout that survive infection and recover become resistant to the disease. The use of this approach to improve brown trout (Salmo trutta) stocking success was tested in three PKD‐affected streams in southern Germany. Fish were treated using local spores of the parasite and kept at low temperatures (14°C) to not develop the disease. Controls were similarly kept but not treated with spores. Independent of time of stocking (winter or spring), recapture rates for both control and parasite‐treated stocked trout were very low (<1%). However, recaptured parasite‐treated trout exhibited lower parasite prevalence than control and wild‐caught trout.

Tetracapsuloides bryosalmonae and proliferative kidney disease in Icelandic salmonids – Comparative data from two different time periods

Tetracapsuloides bryosalmonae is a myxozoan parasite and the causative agent of proliferative kidney disease (PKD), a serious, temperature-dependent and emerging disease affecting salmonid fish. It was first identified in Iceland in 2008, from Arctic charr inhabiting a shallow lowland lake. The aim of this study was to investigate the distribution and prevalence of macroscopic and subclinical T. bryosalmonae infections in Icelandic salmonids and compare different time periods, in context with depths, volumes, altitudes and areas of the lakes and fish age. Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) from 34 lakes, sampled between 1994–1998 and 2009–2017, were examined for macroscopic signs of PKD (n = 2,151) and the presence of T. bryosalmonae infections (n = 1,424). In the earlier period, 43% of lakes (10/23) harboured T. bryosalmonae -infected fish. The mean prevalence in those lakes was 62.1%, being most common in shallow lowland lakes whilst deeper lakes at high altitudes were all free from infection. Only a single fish from one lake showed macroscopic signs of PKD, a shallow lowland lake in southwestern Iceland. In the latter period, T. bryosalmonae was found in 16/18 lakes studied (89%), with a mean prevalence of 78–79% (excluding T.b. free lakes), being most common in the smaller, shallower lakes at lower alttudes. Macroscopic signs of PKD were observed in 11 of 18 of the lakes studied (61%) with prevalences up to 67%, most common in younger fish inhabiting small shallow lowland lakes. The results indicate that the distribution of T. bryosalmonae and the presence of PKD in Iceland have increased over the last few decades. The disease was almost non-existent in the 1990s but has become very common during the last decade or two. With further water temperature increases, as predicted by climate models, PKD is likely to increasingly affect wild salmonid populations in Iceland.

Red blood cells in proliferative kidney disease-rainbow trout (Oncorhynchus mykiss) infected by Tetracapsuloides bryosalmonae harbor IgM+ red blood cells.

The myxozoan parasite Tetracapsuloides bryosalmonae is the causative agent of proliferative kidney disease (PKD)-a disease of salmonid fishes, notably of the commercially farmed rainbow trout Oncorhynchus mykiss. Both wild and farmed salmonids are threatened by this virulent/deadly disease, a chronic immunopathology characterized by massive lymphocyte proliferation and hyperplasia, which manifests as swollen kidneys in susceptible hosts. Studying the immune response towards the parasite helps us understand the causes and consequences of PKD. While examining the B cell population during a seasonal outbreak of PKD, we unexpectedly detected the B cell marker immunoglobulin M (IgM) on red blood cells (RBCs) of infected farmed rainbow trout. Here, we studied the nature of this IgM and this IgM+ cell population. We verified the presence of surface IgM via parallel approaches: flow cytometry, microscopy, and mass spectrometry. The levels of surface IgM (allowing complete resolution of IgM- RBCs from IgM+ RBCs) and frequency of IgM+ RBCs (with up to 99% of RBCs being positive) have not been described before in healthy fishes nor those suffering from disease. To assess the influence of the disease on these cells, we profiled the transcriptomes of teleost RBCs in health and disease. Compared to RBCs originating from healthy fish, PKD fundamentally altered RBCs in their metabolism, adhesion, and innate immune response to inflammation. In summary, RBCs play a larger role in host immunity than previously appreciated. Specifically, our findings indicate that the nucleated RBCs of rainbow trout interact with host IgM and contribute to the immune response in PKD.

Low risk for diabetic complications in type 1 diabetes patients carrying a protective insulin gene variant.

Type 1 diabetes patients carrying a 'protective' insulin gene (INS) variant present a disease endotype with reduced insulin antibody titers, preserved beta cell function and improved glycemic control. We tested whether this protective INS variant associated with lowered risk for development of proliferative diabetic retinopathy (PDR) and diabetic kidney disease (DKD) as long-term diabetic complications. Insulin gene polymorphisms were evaluated in 1,363 type 1 diabetes patients participating in the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications (DCCT/EDIC) study that compared intensive versus conventional insulin therapy in relation with development of PDR and DKD with a follow-up of over two decades. PDR and DKD were absent in type 1 diabetes patients carrying the protective INS variant and receiving intensive insulin therapy (the current standard of clinical care) 1-5 years from their diagnosis (n = 67; mean post-diagnosis follow up of 20.4 ± 1.6 years), versus 11 of 258 patients (4.3%) lacking this variant (20.4 ± 1.8 years follow up). In the secondary intervention group of the intensive therapy arm (1-15 years of disease), PDR was significantly less frequent in carriers of the protective INS variant than those without it (4 of 83 [4.8%] vs. 31 of 260 [11.9%]; p = 0.032; 26.1 ± 3.9 and 26.3 ± 4.1 years follow-up, respectively), whereas DKD frequencies were no different between those with or without this variant (5 of 83 [6.0%] vs. 11 of 260 [4.2%]). Carrying a copy of this protective INS variant further reduces the risk of diabetic complications achieved by intensive insulin therapy and marks a disease endotype with superior glycemic control, increased and extended beta cell function, and prevention of DKD and PDR.

Application of UV-C irradiation prevented a severe outbreak of proliferative kidney disease in rainbow trout aquaculture.

There is an urgent need to establish protocols on how to protect salmonids in aquaculture from outbreaks of proliferative kidney disease (PKD). For this purpose, systems for a continuous application of peracetic acid (PAA, 0.1 mg l-1) and of ultraviolet C light (UV-C, 323.5-158.6 mW s cm-2) were installed in the inlet of raceway-channels within a sub-unit of a commercial rainbow trout Oncorhynchus mykiss farm. After 127 d of rearing, a fish health examination was conducted. Fish in the control and PAA treatment groups showed signs of PKD. In contrast, fish in the UV-C treatment group showed almost no signs of disease based on clinical examinations and necropsy. This observation indicates that UV-C irradiation could be a promising tool to protect fish from PKD in the future.

Evaluation of water temperature under changing climate and its effect on river habitat in a regulated Alpine catchment

Habitat quality of alpine river is largely affected by human activity. The exploitation for hydropower, combined with anthropogenic climate change, canalter mountain riverine ecosystems, leading to less suitable hydro-thermal regimes for the fish. Here, we present a new methodology to assess water temperature within a river featuring water exploitation for hydropower purposes, usable to assess future potential deterioration of riverine habit suitability in response to (increasing) water temperature. We then propose an application focusing upon the case study of the Serio River, in Northern Italy, largely exploited by hydropower productions and highly populated by a very sensitive species, brown trout (Salmo trutta). The methodology proposed involves a set of tools, i.e. i) the hydrological modelPoli-Hydro, to evaluate natural hydrological regime, ii) a hydropower plants scheme to assess river water withdrawal, iii) fish density-environment curves to evaluate the hydraulic suitability in terms of trout potential density for adult, young, and fry as a function of hydraulic features, i.e. depth and velocity, and iv) a new, physically based model,Poli-Wat.Temp, to assess changes in river water temperature, and possible outbreaks of temperature dependant lethal conditions, such as proliferative kidney disease, and others. To provide an assessment of river suitability, possibly complementing (improving?) models based upon solely hydraulic indexes, we propose a new synthetic River Stress index, combining i) potential fish density as driven by hydraulic variables, and ii) thermal suitability. Given that utmost unsuitable conditions (thermally, and likely hydrologically) are expected under future climate conditions pending global warming, we then projected water temperature, and stream flows until the end of the century, in response to socio-economic scenariosof AR6 of the IPCC, to explore the potential for future decrease of river quality. Water temperature would be largely susceptible to climate change with increase up to + 6.5C° in the worst scenarios, while no clear trend is observed for fish density. Overall, potential density would decrease in winter for adults, and in summer for juvenile and fry in downstream sections. Therefore, by coupling hydraulic, and thermal suitability, one finds that i) Alpine rivers would likely face longer critical periods, with respect to those predicted based upon a solely hydraulic habitat based assessment, and ii) continuous temperature increase as projected until the end of the century would result into worse conditions in summer months, seriously endangering fish guilds.

Identification of in vivo induced antigens of the malacosporean parasite Tetracapsuloides bryosalmonae (Cnidaria) using in vivo induced antigen technology.

Tetracapsuloides bryosalmonae is a malacosporean endoparasite that causes proliferative kidney disease (PKD) in wild and farmed salmonids in Europe and North America. The life cycle of T. bryosalmonae completes between invertebrate bryozoan and vertebrate fish hosts. Inside the fish, virulence factors of T. bryosalmonae are induced during infection or interactions with host cells. T. bryosalmonae genes expressed in vivo are likely to be important in fish pathogenesis. Herein, we identify in vivo induced antigens of T. bryosalmonae during infection in brown trout (Salmo trutta) using in vivo induced antigen technology (IVIAT). Brown trout were exposed to the spores of T. bryosalmonae and were sampled at different time points. The pooled sera were first pre-adsorbed with antigens to remove false positive results. Subsequently, adsorbed sera were used to screen a T. bryosalmonae cDNA phage expression library. Immunoscreening analysis revealed 136 immunogenic T. bryosalmonae proteins induced in brown trout during parasite development. They are involved in signal transduction, transport, metabolism, ion-protein binding, protein folding, and also include hypothetical proteins, of so far unknown functions. The identified in vivo induced antigens will be useful in the understanding of T. bryosalmonae pathogenesis during infection in susceptible hosts. Some of the antigens found may have significant implications for the discovery of candidate molecules for the development of potential therapies and preventive measures against T. bryosalmonae in salmonids.

Use of environmental DNA to detect the myxozoan endoparasite Tetracapsuloides bryosalmonae in large Norwegian lakes

AbstractEnvironmental DNA (eDNA) is an increasingly used noninvasive and cost‐effective method for species detections in surveillance studies. The myxozoan endoparasite Tetracapsuloides bryosalmonae is the causative agent of proliferative kidney disease (PKD) in salmonid fish. PKD is a potentially lethal disease of freshwater salmonids when water temperatures exceed 12–14°C for prolonged periods. Periodically, high mortality and decline in farmed and wild salmonid populations in Europe and North America have been reported in the last decades. The aim of this study was to use eDNA as a method to detect Tetracapsuloides bryosalmonae from large, deep, dimictic Norwegian lakes. Such habitats are expected to become increasingly important for cold‐water salmonids with global warming. Samples were collected from five lakes in southeastern Norway, and parasite DNA was detected by qPCR. eDNA from T. bryosalmonae was detected in four of the five lakes surveyed. These findings corresponded with the detection of T. bryosalmonae DNA in salmonid kidneys in four of the lakes in a previous survey. The detection of parasites from eDNA varied between years and stations within the same lake, revealing a changing and apparently stochastic spatial distribution of parasite DNA from year to year. Nonetheless, by sampling multiple sites throughout the lakes, we were able to detect T. bryosalmonae at the lake level in both survey years. Strategies for eDNA sampling in deep, dimictic lakes are discussed.

Genome-wide alternative splicing profile in the posterior kidney of brown trout (Salmo trutta) during proliferative kidney disease

BackgroundThe cnidarian myxozoan parasite Tetracapsuloides bryosalmonae causes chronic proliferative kidney disease (PKD) in salmonids. This parasite is a serious threat to wild and cultured salmonids. T. bryosalmonae undergoes intra-luminal sporogonic development in the kidney of brown trout (Salmo trutta) and the viable spores are released via urine. We investigated the alternative splicing pattern in the posterior kidney of brown trout during PKD.ResultsRNA-seq data were generated from the posterior kidney of brown trout collected at 12 weeks post-exposure to T. bryosalmonae. Subsequently, this data was mapped to the brown trout genome. About 153 significant differently expressed alternatively spliced (DEAS) genes, (delta PSI = 5%, FDR P-value < 0.05) were identified from 19,722 alternatively spliced events. Among the DEAS genes, the least and most abundant alternative splicing types were alternative 5′ splice site (5.23%) and exon skipping (70.59%), respectively. The DEAS genes were significantly enriched for sodium-potassium transporter activity and ion homeostasis (ahcyl1, atp1a3a, atp1a1a.1, and atp1a1a.5). The protein-protein interaction network analysis enriched two local network clusters namely cation transporting ATPase C-terminus and Sodium/potassium ATPase beta chain cluster, and mixed inclusion of Ion homeostasis and EF-hand domain cluster. Furthermore, the human disease-related salmonella infection pathway was significantly enriched in the protein-protein interaction network.ConclusionThis study provides the first baseline information about alternative splicing in brown trout during PKD. The generated data lay a foundation for further functional molecular studies in PKD - brown trout infection model. The information generated from the present study can help to develop therapeutic strategies for PKD in the future.

Reliable Field Assessment of Proliferative Kidney Disease in Wild Brown Trout, Salmo trutta, Populations: When Is the Optimal Sampling Period?

Proliferative kidney disease (PKD), caused by the myxozoan parasite Tetracapsuloides bryosalmonae, is suspected to contribute to the decline of wild brown trout Salmo trutta populations. Different factors need to be taken into consideration for PKD outbreaks. Among them, water temperature appears as a main driver of the disease. To understand the epidemiology and impact of the disease on wild fish populations, reliable sampling approaches to detect the presence of T. bryosalmonae-infected fish are needed. This study aimed to characterize the seasonal variation of the prevalence of T. bryosalmonae-infected fish in brown trout populations in two small streams with differing temperature regimes between upstream and downstream sites. As water temperature is known to influence PKD manifestation in brown trout, we hypothesized that the number of T. bryosalmonae-positive fish, as well as their seasonal distribution, will vary between upper and downstream parts of the two streams. Since, in field studies, results can strongly vary across years, we extended the study over a 3-year-period. The number of infected fish and the intensity of infection were assessed by histology. The results confirmed the hypothesis of pronounced temporal- and site-related differences in the percentage of PKD-positive fish and the intensity of the infection. Comparison of water temperatures (total degree days as well as the number of days with a daily mean temperature ≥15 °C) with PKD data indicated that temperature was the driving factor for the temporal development and the intensity of the infection. A mean of 1500 degree days or 30 days with a daily mean temperature ≥15 °C was required before the infection could be detected histologically. From our findings, recommendations are derived for a water temperature-driven sampling strategy campaigns that enables the detection of PKD infection and prevalence in wild brown trout populations.

Mitigating human impacts including climate change on proliferative kidney disease in salmonids of running waters.

Over the last two decades, an increasing number of reports have identified a decline in salmonid populations, possibly linked to infection with the parasite Tetracapsuloides bryosalmonae and the corresponding disease, that is, proliferative kidney disease (PKD). The life cycle of this myxozoan parasite includes sessile bryozoan species as invertebrate host, which facilitates the distribution of the parasite in running waters. As the disease outcome is temperature dependent, the impact of the disease on salmonid populations is increasing with global warming due to climate change. The goal of this review is to provide a detailed overview of measures to mitigate the effects of PKD on salmonid populations. It first summarizes the parasite life cycle, temperature-driven disease dynamics and new immunological and molecular research into disease resistance and, based on this, discusses management possibilities. Sophisticated management actions focusing on local adaptation of salmonid populations, restoration of the riverine ecosystem and keeping water temperatures cool are necessary to reduce the negative effects of PKD. Such actions include temporary stocking with PKD-resistant salmonids, as this may assist in conserving current populations that fail to reproduce.