Foodborne protozoan parasites in fresh mussels and oysters purchased at retail in Canada.

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 is a risk of infection, especially when shellfish are consumed raw.

Prevalence and molecular characterization of Toxoplasma gondii DNA in retail fresh meats in Canada.

Toxoplasma gondii is a protozoan parasite which infects a wide variety of mammals and birds worldwide, including humans. Human toxoplasmosis is primarily transmitted through the ingestion of tissue cysts in raw or poorly cooked meat and organs of infected animals, or through the ingestion of oocysts in food, water or soil contaminated with cat faeces. There is a distinct paucity of information on the prevalence and molecular characteristics of T. gondii in retail meats in Canada. This study reports the presence of T. gondii DNA in 4.3% (12 of 281) of packages of fresh ground beef, chicken breasts and ground pork purchased at retail in three Canadian provinces. T. gondii prevalence was very similar among all three meat types tested, and among the provinces sampled. Genotyping of positive samples by means of PCR-RFLP and DNA sequencing demonstrated the presence of both T. gondii type II (66.7%) and type III (33.3%). These findings provide baseline data on the prevalence of T. gondii DNA in fresh meats purchased at retail in Canada and will allow for more accurate and meaningful health risk assessments for the purposes of developing food safety guidelines and policies.