Waterborne Protozoan Parasite and Thalassogenic Diseases in Marine Environment: Detection Techniques, Indicators and Public Health Implications

Thalassogenic diseases are human infections associated with exposure to marine environments. This review explores the occurrence of <i>Cryptosporidium</i> spp., <i>Giardia duodenalis</i>, and <i>Blastocystis</i> sp. in seawater and shellfish and their implications for public health. Between 2015 and 2026, multiple studies reported the presence of these parasites in shellfish and seawater. <i>Cryptosporidium</i> spp. was found at average concentrations of 5.5 × 10¹ oocysts/g in shellfish and up to 3.7 × 10¹ oocysts/L in seawater. <i>Giardia duodenalis</i> reached 9.1 × 10¹ cysts/g in shellfish, close to the infectious dose, and 3.5 × 10¹ cysts/L in seawater. <i>Blastocystis</i> sp. showed prevalence rates of 33.82% in shellfish and 17.3% in seawater. These findings highlight a potential infection risk for bathers and seafood consumers, emphasizing the need to determine the specific species (or subtypes) involved and assess their viability to accurately evaluate public health implications. The persistence of these parasites in the environment needs improved monitoring. Future strategies should integrate next-generation sequencing (NGS) or use of various fecal indicators to enhance environmental surveillance and reduce health risks in coastal regions.