Determine mechanisms that allow refugia to exist

Ecology of Infectious Diseases

Collaborative Research: Field and Modeling Studies in Support of
Understanding Disease Resistance in Estuarine Populations and Response to Climate Change

Collecting oysters.

Refugia could exist because 1) parasites are absent from that region of the Bay or 2) parasites are present, but do not develop into lethal infections.

To distinguished between these possibilities, we are collecting oysters from areas in Delaware Bay that we believe may be refugia from disease and comparing them with oysters from known disease areas. We are using PCR technology to signal the presence of parasites on the gills of oysters, and histology (MSX) and culture (Dermo) to identify true infections. The intensity of infections is an index to their lethality.

Finding PCR-positive signals without finding detectable infections suggests that the parasite is present, but unable to successfully develop infections. Finding neither PCR-positive signals nor detectable infections suggests that the parasite may not be present in that location.

Processing oysters for
disease analysis.

Preliminary results indicates that the MSX parasite was much more prevalent than the histological assay showed, indicating that it frequently did not develop infections, even though it was present at the site. Nevertheless, PCR-positive signal were rare or absent in the very upbay and upriver sites, suggesting that the parasite is rarely able to penetrate these very low-salinity sites. The maximum prevalence of PCR signals was comparable among other sites along the bay axis, but with a delayed appeared in an upbay/upriver direction. Potentially lethal infections were rare everywhere.

The Dermo parasite was similarly delayed in appearance upbay, but none of the sites provided refuge from this parasite. Further, the results of culture and PCR assays for this parasite were generally equivalent. Potentially lethal infections were present everywhere, but less prevalent in the low-salinity, upbay and upriver sites.

Delaware Bay sites sampled to identify potential mechanisms that allow refugia to exist. 1 – Hope Creek Bed; 2 – Smyrna River; 3 - Round Island Bed; 4 – Arnolds Bed; 5 - Cohansey River; 6 – Leipsic River; 7 – New Beds; 8 – Cape Shore Lab (natural set).

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