Toxoplasma gondii, Cryptosporidium spp, Cyclospora cayetanensis, Bivalve mollusks, qPCR, Giardia duodenalis, Tunisia, Environmental Monitoring, Animals, Cyclospora - isolation & purification, Toxoplasma - isolation & purification, Cryptosporidium - isolation & purification, Oocysts, Bivalvia - parasitology, Giardia - isolation & purification