Environmental loading rates of the waterborne pathogenic protozoa Cryptosporidium parvum in certain domestic and wildlife species in California

Waterborne transmission of the pathogenic protozoa Cryptosporidium parvum has emerged as an important public health concern. To develop focused strategies to minimize the risk of waterborne transmission of this parasite to humans or animals, a standardized methodology is needed for comparing environmental loading rates for different populations of vertebrate hosts for C. parvum. A reasonable approximation for an estimate of the environmental loading rate is to measure the prevalence of infection and the intensity of shedding using cross-sectional surveys of the mammalian population, and then multiplying by an estimate of fecal production. We applied this concept to a variety of livestock and wildlife species found throughout California. In general we found that regardless of age, striped skunks, coyotes, California ground squirrels, and yellow-bellied marmots were substantial sources of C. parvum oocysts. In contrast, only the young stock of beef and dairy cattle were substantial sources of oocysts; adult cattle appear to excrete only limited numbers oocysts relative to either calves or wildlife. Watershed management plans that endeavor to minimize contamination of drinking water with C. parvum need to focus on appropriate management of wildlife reservoirs of C. parvum in addition to the traditional concern of animal agriculture.