Cryptosporidium parvum transport from cattle fecal deposits on California rangelands

Cryptosporidium parvum is a fecal borne protozoan parasite that can be carried by and cause gastrointestinal illness in humans, cattle, and wildlife. The illness, cryptosporidiosis, can be fatal to persons with compromised immune systems. At question is the potential for C. parvum in cattle fecal deposits on rangeland watersheds to contaminate surface water. First, C. parvum oocysts must be released from fecal deposits during rainfall, becoming available for transport. In 1996, we examined the transport of C. parvum oocysts in overland flow from fecal deposits under natural rainfall and rangeland conditions at the San Joaquin Experimental Range in Madera County, Calif. Our null hypothesis was that C. parvum oocysts are not released from fecal pats and transported 1 m downslope as overland flow with rainfall. Paired plots were located on 10, 20, and 30% slope sites. Each plot was loaded with four, 200 g fecal pats dosed with 10 oocysts g. Pats were placed 1.0 m above the base of each plot. Composite runoff samples from each plot were analyzed for oocyst concentration following each of 4 storm events. Oocysts were transported during each storm. Slope was a significant factor in oocyst transport, with oocyst transport increasing with slope. Although not significant, there was an apparent flushing effect of oocysts across storms, with the majority transported in the first 2 storms. A pilot rainfall simulation experiment also revealed a flushing phenomenon from pats during individual rainfall events. C. parvum oocysts in fecal pats on rangeland can be transported from fecal deposits during rainfall events, becoming available for transport to water-bodies. Future studies need to examine surface and subsurface transport of oocysts on rangeland hillslopes for distances greater than 1 m.