DAO prepress abstract  -  DOI: https://doi.org/10.3354/dao03167

Seawater detection and biological assessments regarding transmission of the oyster parasite Mikrocytos mackini using qPCR

Mark P. Polinski, Gary R. Meyer, Geoffrey J. Lowe, Cathryn L. Abbott*

*Email: cathryn.abbott@dfo-mpo.gc.ca

ABSTRACT: Mikrocytos mackini (Mm) is an intracellular parasite of oysters and causative agent of Denman Island disease in Pacific oysters. Although Mm has been investigated for decades, its natural mode of transmission, mechanism for host entry, and environmental stability are largely unknown. Here we explore these biological characteristics of Mm using a recently described quantitative PCR (qPCR) assay. We identified that Mm could be detected in the flow-through tank water of experimentally infected oysters and during disease remission in host tissues following 6 wk of elevated water temperature. Waterborne exposure of oysters to Mm further confirmed the potential for extracellular seawater transmission of this parasite and also identified host gill to have the highest early and continued prevalence for Mm DNA compared to stomach, mantle, labial palps or adductor muscle samples. However, infections following waterborne challenge were slow to develop despite a substantial exposure (>106 Mm l–1 for 24 h), and further investigation demonstrated that Mm occurrence and infectivity severely declined following extracellular seawater incubation of more than 24 h. This study demonstrates a potential for using qPCR to monitor Mm in wild or farmed oyster populations during periods of disease remission or from environmental seawater samples. This work also suggests that gill tissues may provide a primary site for waterborne entry and possibly shedding of Mm in oysters. Further, although extracellular seawater transmission of Mm was possible, poor environmental stability and infection efficiency likely restricts the geographic transmission of Mm between oysters in natural environs and may help to explain localized areas of infection.