Protozoa in bivalve shellfish: gaps and opportunities to better understand risk to consumers

Protozoan parasites are underrecognized foodborne pathogens that contaminate bivalve shellfish worldwide. This review highlights recent advances in our understanding on the global distribution of shellfish contaminated with Toxoplasma gondii, Cryptosporidium spp., and/or Giardia spp., all of which are zoonotic pathogens that can infect people and marine wildlife. We discuss a framework for estimating the risk of contracting illness from ingestion of protozoa in shellfish and identify critical gaps in current knowledge that must be addressed for accurate risk estimation. Notably, without accounting for parasite viability, risk assessment models are likely to overestimate the true risk of illness, which may result in undue harm to both consumers and the livelihoods of aquaculture producers.