Persistence, impacts and environmental drivers of covert infections in invertebrate hosts

Environmental DNA/RNA for pathogen and parasite detection, surveillance, and ecology

Detection of pathogens, parasites, and other symbionts in environmental samples via eDNA/eRNA (collectively eNA) is an increasingly important source of information about their occurrence and activity. There is great potential for using such detections as a proxy for infection of host organisms in connected habitats, for pathogen monitoring and surveillance, and for early warning systems for disease. However, many factors require consideration, and appropriate methods developed and verified, in order that eNA detections can be reliably interpreted and adopted for surveillance and assessment of disease risk, and potentially inclusion in international standards, such as the World Organisation for Animal Health guidelines. Disease manifestation results from host-symbiont-environment interactions between hosts, demanding a multifactorial approach to interpretation of eNA signals.

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.

PCR-RFLP: a targeted method to reveal host specific malacosporean infection profiles (Cnidaria: Myxozoa: Malacosporea)

Malacosporeans are a group of endoparasitic cnidarians (Myxozoa) that use freshwater bryozoans and fish as final and intermediate hosts, respectively. The malacosporean Tetracapsuloides bryosalmonae causes proliferative kidney disease (PKD), an emerging disease in aquaculture and wild fish populations, including threatened salmonids in Europe and the USA. Mixed infections of malacosporeans are often encountered, and a monitoring tool for screening of multiple malacosporean species in either their fish or bryozoan hosts is therefore desirable. We describe an inexpensive method that combines PCR amplification of the partial 18S rRNA gene (~260 bp) and a single-step restriction fragment length polymorphism (RFLP) method for identification of 10 malacosporean lineages and species. We demonstrate and test this methodology on a set of DNA extracted from malacosporeans infecting fish kidney and tissues sampled from bryozoan colonies and compare the results with Sanger sequencing of the same parasite DNA isolates. The PCR-RFLP and Sanger sequencing methods agreed in 100% of cases. The PCR-RFLP method offers a number of opportunities, including screening large panels of host tissue samples to gain insights into infection patterns, characterizing mixed infections, and confirming highly pathogenic T. bryosalmonae infections. The method can also be further refined as new sequence data become available for malacosporeans.

Transcriptome Analysis Elucidates the Key Responses of Bryozoan Fredericella sultana during the Development of Tetracapsuloides bryosalmonae (Myxozoa)

Bryozoans are sessile, filter-feeding, and colony-building invertebrate organisms. Fredericella sultana is a well known primary host of the myxozoan parasite Tetracapsuloides bryosalmonae. There have been no attempts to identify the cellular responses induced in F. sultana during the T. bryosalmonae development. We therefore performed transcriptome analysis with the aim of identifying candidate genes and biological pathways of F. sultana involved in the response to T. bryosalmonae. A total of 1166 differentially up- and downregulated genes were identified in the infected F. sultana. Gene ontology of biological processes of upregulated genes pointed to the involvement of the innate immune response, establishment of protein localization, and ribosome biogenesis, while the downregulated genes were involved in mitotic spindle assembly, viral entry into the host cell, and response to nitric oxide. Eukaryotic Initiation Factor 2 signaling was identified as a top canonical pathway and MYCN as a top upstream regulator in the differentially expressed genes. Our study provides the first transcriptional profiling data on the F. sultana zooid's response to T. bryosalmonae. Pathways and upstream regulators help us to understand the complex interplay in the infected F. sultana. The results will facilitate the elucidation of innate immune mechanisms of bryozoan and will lay a foundation for further analyses on bryozoan-responsive candidate genes, which will be an important resource for the comparative analysis of gene expression in bryozoans.

Iflavirus Covert Infection Increases Susceptibility to Nucleopolyhedrovirus Disease in Spodoptera exigua

Naturally occurring covert infections in lepidopteran populations can involve multiple viruses with potentially different transmission strategies. In this study, we characterized covert infection by two RNA viruses, Spodoptera exigua iflavirus 1 (SeIV-1) and Spodoptera exigua iflavirus 2 (SeIV-2) (family Iflaviridae) that naturally infect populations of Spodoptera exigua, and examined their influence on susceptibility to patent disease by the nucleopolyhedrovirus Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV) (family Baculoviridae). The abundance of SeIV-1 genomes increased up to ten-thousand-fold across insect developmental stages after surface contamination of host eggs with a mixture of SeIV-1 and SeIV-2 particles, whereas the abundance of SeIV-2 remained constant across all developmental stages. Low levels of SeIV-2 infection were detected in all groups of insects, including those that hatched from surface-decontaminated egg masses. SeIV-1 infection resulted in reduced larval weight gain, and an unbalanced sex ratio, whereas larval developmental time, pupal weight, and adult emergence and fecundity were not significantly affected in infected adults. The inoculation of S. exigua egg masses with iflavirus, followed by a subsequent infection with SeMNPV, resulted in an additive effect on larval mortality. The 50% lethal concentration (LC50) of SeMNPV was reduced nearly 4-fold and the mean time to death was faster by 12 h in iflavirus-treated insects. These results suggest that inapparent iflavirus infections may be able to modulate the host response to a new pathogen, a finding that has particular relevance to the use of SeMNPV as the basis for biological pest control products.

Virin HSK and Helicovex SK – efficacy and safety of baculovirus-based bioinsecticides

Insect pest control is a key mechanism to give humans advantage over insects in competition for food resources. Bioinsecticides are highly virulent in target insects, can control their populations and prevent a sharp increase in their number. The bioinsecticide Virin HSK was created in FBRI SRC VB “Vector”. Helicoverpa zea single nuclear polyhedrosis virus strain HS-18 is the active basis for Virin HSK. Here we studied the effectiveness of Helicovex SK and Virin HSK bioinsecticides as cotton bollworms control agent in comparison with the chemical insecticide Pirinex, CE and determined the safety of these insectisides for the entomophage. The flow rate of the working fluid was 200 l/ha. Helicovex SK and Virin HSK protected soybean during bean ripening and corn in the period from wax ripeness to harvesting. Helicovex SK and Virin HSK had higher efficiency than Pirinex KE.

The Malacosporean Myxozoan Parasite Tetracapsuloides bryosalmonae: A Threat to Wild Salmonids

Tetracapsuloides bryosalmonae is a myxozoan parasite responsible for proliferative kidney disease (PKD) in a wide range of salmonids. PKD, characterized by high mortality and morbidity, is well known for affecting aquaculture operations and wild salmonid populations across Europe and North America. The life cycle of T. bryosalmonae revolves around freshwater bryozoan and salmonid fish hosts. In recent years, T. bryosalmonae has been reported among wild salmonids from the European countries where it has not been reported previously. T. bryosalmonae is believed to be a possible reason for the diminishing wild salmonid populations in the natural water bodies of many European countries. Climate crisis driven rising water temperature can further accelerate the distribution of T. bryosalmonae. Expansion of the geographical distribution of T. bryosalmonae may further advocate the decline of wild salmonid populations, especially brown trout (Salmo trutta) in their habitats. Mathematical models are used to understand the pattern and distribution of T. bryosalmonae among the host in the natural water bodies. The present manuscript not only summarizes the incidences of T. bryosalmonae among the wild salmonid populations, but also discusses the contemporary understanding about the development of T. bryosalmonae in its hosts and the influences of various factors in the spread of the disease in the wild.

To remain or leave: Dispersal variation and its genetic consequences in benthic freshwater invertebrates

Variation in dispersal capacity may influence population genetic variation and relatedness of freshwater animals thus demonstrating how life-history traits influence patterns and processes that in turn influence biodiversity. The majority of studies have focused on the consequences of dispersal variation in taxa inhabiting riverine systems whose dendritic nature and upstream/downstream gradients facilitate characterizing populations along networks. We undertook extensive, large-scale investigations of the impacts of hydrological connectivity on population genetic variation in two freshwater bryozoan species whose dispersive propagules (statoblasts) are either attached to surfaces (Fredericella sultana) or are released as buoyant stages (Cristatella mucedo) and that live primarily in either lotic (F. sultana) or lentic environments (C. mucedo). Describing population genetic structure in multiple sites characterized by varying degrees of hydrological connectivity within each of three (or four) UK regions enabled us to test the following hypotheses: (1) genetic diversity and gene flow will be more influenced by hydrological connectivity in populations of C. mucedo (because F. sultana dispersal stages are retained); (2) populations of F. sultana will be characterized by greater genetic divergence than those of C. mucedo (reflecting their relative dispersal capacities); and (3) genetic variation will be greatest in F. sultana (reflecting a propensity for genetic divergence as a result of its low dispersal potential). We found that hydrological connectivity enhanced genetic diversity and gene flow among C. mucedo populations but not in F. sultana while higher overall measures of clonal diversity and greater genetic divergence characterized populations of F. sultana. We suggest that genetic divergence over time within F. sultana populations reflects a general constraint of releasing propagules that might eventually be swept to sea when taxa inhabit running waters. In contrast, taxa that primarily inhabit lakes and ponds may colonize across hydrologically connected regions, establishing genetically related populations. Our study contributes more nuanced views about drivers of population genetic structures in passively dispersing freshwater invertebrates as outlined by the Monopolization Hypothesis (Acta Oecologica, 23, 2002, 121) by highlighting how a range of demographic and evolutionary processes reflect life-history attributes of benthic colonial invertebrates (bryozoans) and cyclically parthenogenetic zooplankton. In addition, growing evidence that genetic divergence may commonly characterize populations of diverse groups of riverine taxa suggests that organisms inhabiting lotic systems may be particularly challenged by environmental change. Such change may predispose riverine populations to extinction as a result of genetic divergence combined with limited dispersal and gene flow.

OPEN RESEARCH BADGES

This article has earned an Open Data Badge for making publicly available the digitally-shareable data necessary to reproduce the reported results. The data is available at https://doi.org/10.5061/dryad.1tm8705.