Seasonal Temperature Fluctuations Induces Rapid Inactivation ofCryptosporidium parvum

Abstract

This study measured the inactivation rate of bovine genotype A Cryptosporidium parvum oocysts attributable to diurnal oscillations of ambient temperature and solar radiation typical of California rangelands and dairies from spring through autumn. We first measured the relationship between air temperature and the internal temperature of bovine feces exposed to sunlight on commercial operations throughout California. Once maximum air temperature exceeded the mid 20 degrees C, diurnal thermal regimes of bovine fecal material exhibited peaks of over 40, 50, 60, and 70 degrees C. These diurnal thermal regimes were emulated using a thermocycler, with oocysts suspended in distilled water or fecal-water mix. Using oral inoculations of 10(5) C. parvum oocysts per neonatal Balb/c mouse (>1000-fold the ID50), no infections were observed using 1 to 5-day cycles of these thermal regimes. Loss of infectivity induced bythese thermal regimes was primarily due to partial or complete in vitro excystation during the first 24-h diurnal cycle and secondarily to thermal inactivation of the remaining intact or partial oocysts. These results suggest that as ambient conditions generate internal fecal temperatures > or = 40 degrees C via conduction, radiation, and convection, rapid environmental inactivation occurs at a rate of > or = 3.27 log reduction d(-1) for C. parvum oocysts deposited in the feces of cattle.

Management reducesE. coliin irrigated pasture runoff

“…The timing of pasture grazing by beef cattle was managed to create a range of total days rest between grazing and irrigation of the pasture. This allowed us to characterize the potential reduction of E. coli in tailwater attributable to such processes as the background mortality rate of E. coli, and the drying and heating of fecal pats during the summer season (Li et al 2005).…”

“…For example, the E. coli concentration was 23% lower after 9 days of rest than after 1 day of rest, but only 2% lower after each additional day of rest. This reduction was likely due to two primary processes: (1) as cattle fecal pats age, the microbial pollutants in them naturally die off (Li et al 2005;Meays et al 2005), and (2) as the pats dry, they develop shells that trap the bacteria inside.…”

Effect of Daily Temperature Fluctuation during the Cool Season on the Infectivity of Cryptosporidium parvum

“…As described previously (23), air temperature and internal temperature data for bovine fecal pats that were exposed to sunlight were collected for 12 months using an Optic StowAway Temp Logger system (Onset Computer Corporation, Bourne, MA) at 11 commercial diary and cow-calf operations throughout California.…”

“…To complement this work, we previously investigated the impact of large daily changes in the ambient temperature on C. parvum oocyst infectivity, using spring through autumn thermal regimens and temperatures measured inside bovine fecal pats that were exposed to solar radiation at cowcalf and dairy production facilities (23). Under California's summer climatic conditions, internal fecal pat temperatures range from 45°C to 75°C during the day and decrease 10 to 60°C during the night.…”

“…Under California's summer climatic conditions, internal fecal pat temperatures range from 45°C to 75°C during the day and decrease 10 to 60°C during the night. Exposing oocysts to these large thermal fluctuations results in Ͼ3.3-log 10 reductions in oocyst infectivity in each 24-h cycle (23). The present study was conducted in order to measure the effect of exposure to oocysts to coolseason daily temperatures (with peaks at temperatures greater than 10°C, 20°C, and 30°C) on the rate of inactivation of C. parvum oocysts.…”