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Title: Die-off rates of Cryptosporidium parvum oocysts in a swine lagoon and in a spray field

item Jenkins, Michael
item LIOTTA, JANICE - Cornell University
item BOWMAN, DWIGHT - Cornell University

Submitted to: American Society for Microbiology General Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 2/28/2011
Publication Date: 5/24/2011
Citation: Jenkins, M., Liotta, J., Bowman, D. 2011. Die-off rates of Cryptosporidium parvum oocysts in a swine lagoon and in a spray field [abstract]. American Society for Microbiology 111th General Meeting, May 21-24, 2011, New Orleans, LA. CDROM.

Interpretive Summary:

Technical Abstract: Background: Because of several large-scale outbreaks of cryptosporidiosis in humans, Cryptosporidium has become a public health concern. Commercial swine operations apply large volumes of effluent from lagoons to spray fields as a waste management practice. This effluent is a source of Cryptosporidium oocysts, the survival stage of this parasite. A load of a billion viable, infectious oocysts can contaminate a field which can lead to the contamination of surface waters. Although the species distribution of Cryptosporidium is likely dominated by C. suis, a fraction may be comprised of the zoonotic C. parvum which can infect humans. To better understand the survival dynamics of Cryptosporidium oocysts associated with swine operations, experiments were performed to determine die-off rates of C. parvum oocysts in a swine lagoon and its adjacent spray field. Methods: Lagoon effluent from a farrowing operation was inoculated with C. parvum. Sentinel chambers containing this inoculated effluent at 4(10)6 oocysts per chamber were submerged in a lagoon. At weekly intervals triplicate chambers were removed, oocysts extracted, and assayed for viability. Two experiments were conducted, one summer of 2009, and another in winter of 2009. As a control oocysts suspended in water and kept at 5ºC were assayed at each sampling time. For the spray field experiment, surface soil from the field was air-dried, sieved, and placed in sentinel chambers. Soil in the chambers was hydrated to field capacity, then inoculated with lagoon effluent containing 4(10)6 viable C. parvum oocysts per chamber. Chambers were buried 1.5 cm below the soil surface in three blocks. As controls, microcentrifuge tubes containing oocysts suspended in water were buried with the sentinel chambers. Triplicate chambers (one per block) and controls were removed at designated times, the oocysts extracted, and assayed for viability. Based on first order decay equations, die-off rates were determined and days to reach 99% die-off were calculated. Results: Die-off rate coefficients for the summer and winter lagoon experiments were 0.3504 week-1 (R2 = 0.98) and 0.2292 week-1 (R2 = 0.99); based on these coefficients, the time to reach 99% die-off was 13.1 weeks, and 20.1 weeks, respectively. Based on one spray field experiment, a die-off rate coefficient for oocysts in soil was 0.0841 day-1; and days to reach 99% die-off was 7.8 weeks. The die-off rate coefficient for the controls was 0.0354 day-1, and days to reach 99% die off was 18.6 weeks. Conclusion: Oocyst die off in soil was quicker in soil than in the lagoon. Applying this knowledge to management of swine effluent can decrease the potential public health hazard that a swine operation may pose in a watershed, and decrease the probability of contaminating surface water with infectious Cryptosporidium.