Giardia and Cryptosporidium can both infect mammals if the oocysts are ingested. Urban runoff may convey cysts from litter and domestic pet excreta. Periodically, treatment facilities may find it necessary to bypass treatment of their wastewater. In this case, water containing protozoan cysts is discharged directly into the surface water body. Cysts in overland flow can be transported freely and within organic particles.
Overland flow is the most direct route for protozoan transportation.
Underground flow is less direct because water flow and cyst passage are impeded by soil permeability and porosity constraints. Ingestion of shellfish. Current methods for protozoan detection are poorly standardized. Isolation and identification of protozoa is difficult because they are relatively few in number, even in polluted water. Instead, other more plentiful organisms such as total coliforms, fecal coliform, and fecal streptococci are often used as indicator organisms.