Estimating Environmental Loading Rates of the Waterborne Pathogenic Protozoa, Cryptosporidium Parvum, in Certain Domestic and Wildlife Species in California

Cryptosporidium parvum (C. parvum) is a protozoal parasite that can cause gastrointestinal illness in a wide variety of mammals, including humans, livestock, companion animals, and wildlife. New species of Cryptosporidium are constantly being discovered, such as C. canis and C. felis, but their significance relative to the large role that C. parvum plays in livestock and human cryptosporidiosis is still unclear. In the majority of livestock species, clinical disease and shedding of C. parvum typically occurs in youngstock under a few months of age, but fecal shedding of oocysts can also occur in healthy older animals which can then serve as a source of infection for these younger animals. In humans, clinical disease and shedding can appear at all ages, but is typically more common among children. The predominant clinical sign is profuse, watery diarrhea lasting from a few days to several weeks in normal (immunocompetent) individuals, but can be prolonged and life threatening among immunocompromised hosts such as AIDS patients. Modes of transmission range from direct fecal-oral transmission, as might occur between infected and susceptible calves during lay behavior, or ingestion of food or water inadvertently contaminated with oocysts from the feces of an infected host.Waterborne transmission of the pathogenic protozoa, Cryptosporidium parvum, has emerged as an important public health concern. Because the infectious stage of C. parvum (oocysts) is resistant to conventional water treatment processes, public health agencies and water districts are actively seeking methods of reducing surface water contamination with this parasite. Protection of source water such as rivers and lakes has the potential to reduce the risk of transmission to humans and animals through drinking water, as well as through human recreational contact with untreated water. Given that the parasite readily infects a large number of mammalian hosts (Fayer et al. 1997), there are a number of possible