Determination of Cryptosporidium spp. oocyst levels in the Hillsborough River, PEI

Principal Investigators: Spencer Greenwood & Juan Aguirre
Co-Investigators: Javier Sanchez, Henrik Stryhn, J McClure, Jeffrey Davidson & Jessica Willis

Contamination of oysters in coastal or estuarine environments occurs predominantly via wastewater sewage discharge and agricultural run-off from farms. Cryptosporidium is a parasite that causes gastrointestinal illness and has been detected in many shellfish species in both fecal-contaminated and clean oyster growing areas across the globe. Despite this, no data are available on parasite oocyst concentrations in harvest-zone waters or in oysters harvested in PEI. An assessment of the levels of this parasite in areas where the health authorities permit oyster harvesting is an important public health concern.

We conducted a longitudinal study to determine the levels of Cryptosporidium oocyst contamination at two different times during the spring Eastern oyster harvesting season of 2014 in PEI. In each oyster fishery zone (prohibited, restricted, and approved) in the Hillsborough River system, three water samples were taken 1 day before a predicted day of precipitation (≥15mm/h forecast prediction by Environment Canada) and 1, 3, and 7 days after the rain event ended. Preliminary analysis found no significant differences in Cryptosporidium oocyst counts among the three zones and sampling times during the study. A significant increase in oocyst counts was observed, however, after an intense rain event, at which time they were almost two times higher than after a mild rain event. Official guidelines do not currently apply to Cryptosporidium counts in harvested shellfish; however, our findings suggest that authorities should develop guidelines that require public health officials to test for this parasite in potentially contaminated shellfish or waters, especially those harvested after heavy rain events.