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A rapid phenotype change in the pathogen Perkinsus marinus was associated with a historically significant marine
Ryan B Carnegie1, Susan E Ford2, Rita K Crockett3
1Virginia Institute of Marine Science, William & Mary, P.O. Box 1346, Gloucester Point, VA, 23062, USA. carnegie@vims.edu.
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.
Insights
A hypervirulent Perkinsus marinus (dermo disease) strain emerged in oysters, increasing disease intensity and mortality. This adaptation likely occurred due to environmental changes and competition from invasive pathogens.
Area of Science:
- Marine biology
- Pathogen evolution
- Ecosystem dynamics
Background:
- Perkinsus marinus causes significant ecological and economic damage to Crassostrea virginica (oysters).
- The intensification of dermo disease in the USA since the 1980s lacked a clear explanation, with climatic factors proving insufficient.
- The establishment of the invasive pathogen Haplosporidium nelsoni in 1959 impacted oyster populations.
Purpose of the Study:
- To investigate the cause of the rapid and persistent intensification of dermo disease.
- To identify potential changes in the Perkinsus marinus parasite.
- To understand the adaptive responses of native parasites to ecosystem disturbances.
Main Methods:
- Retrospective histopathology analysis of 8355 archival oyster samples from 1960 to 2018.
- Geographic scope included Chesapeake Bay, South Carolina, and New Jersey.
- Comparison of parasite phenotypes before and after major dermo disease outbreaks.
Main Results:
- A novel, hypervirulent P. marinus phenotype emerged between 1983 and 1990.
- This emergence coincided with major dermo disease outbreaks and increased oyster mortality.
- Phenotypic changes included a shortened parasite life cycle and a shift in tissue tropism to digestive epithelia.
Conclusions:
- The emergence of a hypervirulent P. marinus phenotype explains the intensified dermo disease.
- These adaptive changes in the native parasite were likely influenced by reduced oyster availability and the presence of H. nelsoni.
- This study suggests a novel host-parasite interaction: increased native parasite virulence as an ecosystem response to invasion.
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