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Title: Inactivation of Cryptosporidium parvum oocysts in field soil

Author
item Kato, S.
item Jenkins, Michael
item Ghiorse, W.
item Fogarty, E.
item Bowman, D.

Submitted to: Southeast Asian Journal of Tropical Medicine and Public Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2001
Publication Date: 9/11/2001
Citation: Kato, S., Jenkins, M., Ghiorse, W.C., Fogarty, E.A., Bowman, D.D. 2001. Inactivation of Cryptosporidium parvum oocysts in field soil. Southeast Asian Journal of Tropical Medicine and Public Health. 32(Suppl 2):183-189.

Interpretive Summary: Cryptosporidium parvum is a protozoan parasite that threatens the quality of municipal drinking water. Dairies and neonatal calves have been identified as potential sources of C. parvum oocysts, the transmissive form of the parasite. Before oocysts reach surface waters they are generally deposited in fecal material on soil. Little is known about the survival kinetics of C. parvum oocysts in soil. A field study was established to determine the effects of soil water potential, pH, and ammonia on the inactivation of oocysts. Oocysts purified from infected calf feces were inoculated into sentinel chambers that were designed to contain pathogens in a soil substrate and equilibrate with the external environment. The inoculated chambers were buried 4 cm below the surface on a hillside of an old farm site at 25 points, 20 m apart, on a 5 x 5 grid. Chambers were removed and oocysts assayed for potential infectivity at, 0, 2, 7, 19, 33, 66, and 152 days after placement. A three-dimensional mapping program was used to create 3-D maps of the viabilities of C. parvum oocysts and other factors measured during the experiment. The 3-D graphical representation indicated areas in the field where oocyst inactivation was the least and the greatest; however, a correlation between oocyst survival and the three soil parameters that were measured did not exist.

Technical Abstract: Cryptosporidium parvum oocysts from dairy calves are believed to regularly contaminate watersheds. Identifying oocysts and measuring their viability in the natural environment are important elements in estimating the risk posed by this resistant organism. A 152 day field study was conducted to measure the viabilities of oocysts inoculated into 25 sampling points. Water potential, pH, and ammonium content were also measured at the same 25 sampling sites. A three-dimensional mapping program (Surfer®) was used to create 3-D maps of the viabilities of C. parvum oocysts and other factors measured during the experiment. The results indicate that 3-D graphical presentation may be a useful means to identify potential sites of greatest risk of oocyst survival and could indicate areas where natural conditions are causing the most rapid oocyst inactivation, and this method can be a means for the future measurement of microorganism inactivation in the natural environment. The maps, however, indicated no correlation between viability and the three soil parameters that were measured. Oocyst survival was greater in the field soil than in water (the controls).