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A rapid phenotype change in the pathogen Perkinsus marinus was associated with a historically significant marine disease emergence in the eastern oyster.

ABSTRACT: The protozoan parasite Perkinsus marinus, which causes dermo disease in Crassostrea virginica, is one of the most ecologically important and economically destructive marine pathogens. The rapid and persistent intensification of dermo in the USA in the 1980s has long been enigmatic. Attributed originally to the effects of multi-year drought, climatic factors fail to fully explain the geographic extent of dermo's intensification or the persistence of its intensified activity. Here we show that emergence of a unique, hypervirulent P. marinus phenotype was associated with the increase in prevalence and intensity of this disease and associated mortality. Retrospective histopathology of 8355 archival oysters from 1960 to 2018 spanning Chesapeake Bay, South Carolina, and New Jersey revealed that a new parasite phenotype emerged between 1983 and 1990, concurrent with major historical dermo disease outbreaks. Phenotypic changes included a shortening of the parasite's life cycle and a tropism shift from deeper connective tissues to digestive epithelia. The changes are likely adaptive with regard to the reduced oyster abundance and longevity faced by P. marinus after rapid establishment of exotic pathogen Haplosporidium nelsoni in 1959. Our findings, we hypothesize, illustrate a novel ecosystem response to a marine parasite invasion: an increase in virulence in a native parasite.

SUBMITTER: Carnegie RB

PROVIDER: S-EPMC8213716 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Perkinsus marinus is a protozoan parasite of molluscs that can be propagated in vitro in a defined culture medium, in the absence of host cells. We previously reported that P. marinus trophozoites can be transfected with high efficiency by electroporation using a plasmid based on MOE, a highly expressed gene, and proposed its potential use as a "pseudoparasite." This is a novel gene expression platform for parasites of medical relevance for which the choice of the surrogate organism is based on phylogenetic affinity to the parasite of interest, while taking advantage of the whole engineered surrogate organism as a vaccination adjuvant. Here we improved the original transfection plasmid by incorporating a multicloning site, an enterokinase recognition sequence upstream of GFP, and a His-tag and demonstrate its potential suitability for the heterologous expression of Plasmodium sp. genes relevant to the development of anti-malarial vaccines. Plasmodium berghei HAP2 and MSP8, currently considered candidate genes for a malaria vaccine, were cloned into p[MOE]:GFP, and the constructs were used to transfect P. marinus trophozoites. Within 48 hr of transfection we observed fluorescent cells indicating that the P. berghei genes fused to GFP were expressed. The expression appeared to be transient for both P. berghei genes, as florescence of the transfectants diminished gradually over time. Although this heterologous expression system will require optimization for integration and constitutive expression of Plasmodium genes, our results represent attainment of proof for the "pseudoparasite" concept we previously proposed, as we show that the engineered P. marinus system has the potential to become a surrogate system suitable for expression of Plasmodium spp. genes of interest, which could eventually be used as a malaria vaccine delivery platform. The aim of the present study was to test the ability of marine protozoan parasite P. marinus to express genes of P. berghei .

Project description:BackgroundChanges in climate are predicted to influence parasite and pathogen infection patterns in terrestrial and marine environments. Increases in temperature in particular may greatly alter biological processes, such as host-parasite interactions. For example, parasites could differentially benefit from increased reproduction and transmission or hosts could benefit from elevated immune responses that may mediate or even eliminate infections. In the southeastern United States, the Eastern oyster, Crassostrea virginica, is infected by the lethal protozoan parasite, Perkinsus marinus. Under field conditions, intertidal (air-exposed) oysters have been found to have significantly higher P. marinus infection intensity and marginally higher infection prevalence than subtidal (submerged) oysters. During summer, air temperatures are much warmer than water and this exposure of intertidal oysters to higher temperatures is a suggested mechanism for increased infection intensity.MethodsWe simulated intertidal exposure using controlled laboratory experiments to determine how host traits (survival and immune response) and parasite infection intensity will respond to elevated air temperature ranging from 27 °C to 53 °C during emersion at low tide. In Georgia, where our work was conducted, the average summer water temperature is 29 °C and the average maximum high air temperature in July is 33 °C (though oysters have been shown to survive at much higher air temperatures).ResultsHost survival declined as temperature increased, with a definitive drop-off between 39-43 °C. Negative effects of air temperature on host immune response (phagocytic activity) were detectable only at extremely high temperatures (47-50 °C) when hosts were suffering acute mortality. Parasite infection intensity peaked at 35 °C.DiscussionOur results suggest that an increase in average summer air temperature to 35 °C or higher could affect oyster survival directly through temperature-related impacts in the short-term and indirectly through increased P. marinus infection intensity over the long-term.

Project description:BACKGROUND: Perkinsus marinus, a protozoan parasite of the eastern oyster Crassostrea virginica, has devastated natural and farmed oyster populations along the Atlantic and Gulf coasts of the United States. It is classified as a member of the Perkinsozoa, a recently established phylum considered close to the ancestor of ciliates, dinoflagellates, and apicomplexans, and a key taxon for understanding unique adaptations (e.g. parasitism) within the Alveolata. Despite intense parasite pressure, no disease-resistant oysters have been identified and no effective therapies have been developed to date. RESULTS: To gain insight into the biological basis of the parasite's virulence and pathogenesis mechanisms, and to identify genes encoding potential targets for intervention, we generated>31,000 5' expressed sequence tags (ESTs) derived from four trophozoite libraries generated from two P. marinus strains. Trimming and clustering of the sequence tags yielded 7,863 unique sequences, some of which carry a spliced leader. Similarity searches revealed that 55% of these had hits in protein sequence databases, of which 1,729 had their best hit with proteins from the chromalveolates (E-value<or=1e-5). Some sequences are similar to those proven to be targets for effective intervention in other protozoan parasites, and include not only proteases, antioxidant enzymes, and heat shock proteins, but also those associated with relict plastids, such as acetyl-CoA carboxylase and methyl erythrithol phosphate pathway components, and those involved in glycan assembly, protein folding/secretion, and parasite-host interactions. CONCLUSIONS: Our transcriptome analysis of P. marinus, the first for any member of the Perkinsozoa, contributes new insight into its biology and taxonomic position. It provides a very informative, albeit preliminary, glimpse into the expression of genes encoding functionally relevant proteins as potential targets for chemotherapy, and evidence for the presence of a relict plastid. Further, although P. marinus sequences display significant similarity to those from both apicomplexans and dinoflagellates, the presence of trans-spliced transcripts confirms the previously established affinities with the latter. The EST analysis reported herein, together with the recently completed sequence of the P. marinus genome and the development of transfection methodology, should result in improved intervention strategies against dermo disease.

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A rapid phenotype change in the pathogen Perkinsus marinus was associated with a historically significant marine disease emergence in the eastern oyster.

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