The introduction of Asian oysters (Crassostrea
ariakensis) to the waters of the Chesapeake Bay holds
potential benefits to the environment as well as public
health risks, according to a study by researchers at the
Johns Hopkins Bloomberg
School of Public Health.
Findings showed that C. ariakensis, when grown in
aquacultures, effectively and efficiently remove human
pathogens from the water. However, the researchers also
found that some human pathogens accumulated and persisted
in Asian oysters up to five times longer than in native
oysters. They concluded that the nonnative oysters could
pose a health threat if harvested from polluted waters and
consumed raw. The study is the first to examine the public
health impact of nonnative oysters in the Chesapeake Bay
and is published in the May edition of Applied and
Environmental Microbiology.
Some policy-makers have proposed introducing the C.
ariakensis to replace the dwindling population of the
native oyster, C. virginica. The study authors note that C.
ariakensis holds promise for rebuilding the oyster
harvesting industry because it grows to market size in one
year, half the time it takes native oysters to reach market
size.
"Introducing nonnative oysters to the Chesapeake Bay
is filled with unknowns and may have unintended
consequences," said Thaddeus K. Graczyk, associate
professor in the Bloomberg School's departments of
Environmental Health Sciences, and
Molecular Microbiology and Immunology. "Our study
indicated that nonnative oysters could provide excellent
ecological services in regard to cleaning the bay of
infectious agents. However, these environmental benefits
are associated with public health risk when these oysters
are intended for human consumption."
The study was conducted by observing commercial-sized
C. ariakensis in a 30-gallon tank of water. The oysters
were exposed to varying levels of water salinity to
simulate conditions in the Chesapeake Bay and to several
human pathogens, including Cryptosporidium and Giardia
lamblia, which are common causes of diarrhea, and several
microsporidian parasites known to cause illness in
humans.
According to the study, Cryptosporidium continued to
be detected in the nonnative oysters up to 33 days after
exposure in the water. Giardia lamblia cysts were
detectable up to 14 days following exposure.
The study was written by Graczyk, Autumn S. Girouard,
Leena Tamang, Sharon P. Nappier and Kellogg Schwab. It was
supported by grants from the NOAA Chesapeake Bay Office,
the NATO Collaborative Linkage Grant, the Johns Hopkins
Center in Urban Environmental Health and the Alternatives
Research and Development Foundation.
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