Scientific Publications
Foodborn protozoan parasites in fresh mussels and oysters purchased at retail in Canada
International Journal of Food Microbiology, 399, 110248
Studies worldwide have reported the presence of protozoan parasites in a variety of
commercial bivalve shellfish. The uptake of these parasites by shellfish occurs during
filter feeding in faecally-contaminated waters. The objective of the present study was to
determine the prevalence of Giardia, Cryptosporidium and Toxoplasma in fresh, live
shellfish purchased in three Canadian provinces as part of the retail surveillance
activities led by FoodNet Canada (Public Health Agency of Canada). Packages
containing mussels (n=253) or oysters (n=130) were purchased at grocery stores in
FoodNet Canada sentinel sites on a biweekly basis throughout 2018 and 2019, and
shipped in coolers to Health Canada for testing. A small number of packages were not
tested due to insufficient quantity or poor quality. Following DNA extraction from
homogenized, pooled tissues, nested PCR and DNA sequencing were used to detect
parasite-specific sequences. Epifluorescence microscopy was used to confirm the
presence of intact cysts and oocysts in sequence-confirmed PCR-positive samples.
Giardia duodenalis DNA was present in 2.4% of 247 packages of mussels and 4.0% of
125 packages of oysters, while Cryptosporidium parvum DNA was present in 5.3% of
247 packages of mussels and 7.2% of 125 packages of oysters. Toxoplasma gondii
DNA was only found in mussels in 2018 (1.6% of 249 packages). Parasite DNA was
detected in shellfish purchased in all three Canadian provinces sampled, and there
was no apparent seasonal variation in prevalence. While the present study did not test
for viability, parasites are known to survive for long periods in the marine environment,
and these findings suggest that there may be some risk of infection especially when
shellfish are consumed raw.
International Journal of Food Microbiology, 399, 110248
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