Evaluation of the Effect of Temperature on the Die-Off Rate for Cryptosporidium parvum Oocysts in Water, Soils, and Feces

Abstract

2The zoonotic protozoan parasite Cryptosporidium parvum poses a significant risk to public health and has become a global concern for water resource management (10). In order to identify the risk of potential contamination, knowledge about the survival of Cryptosporidium oocysts in the environment is required. Cryptosporidium oocysts can retain infectivity for months and resist environmental stresses more readily than many other pathogens because of a hard protective wall (10,15,41). As a result, the characterization of the die-off dynamics of C. parvum oocysts in the environment has received much attention (26). In this paper, we review the published data of the last two decades and the derived understanding of the relationships between temperature, one of the most important environmental stresses, and the die-off of C. parvum in water, soils, and feces.In general, the inactivation of Cryptosporidium oocysts in the environment slows down exponentially with time, presenting shoulder and tailing effects (31,38). To cater for these two functions, a first-order exponential formula has usually been used to simulate the die-off curves for oocysts in water (5, 9, 18, 21), in soils (8,20,28), and in feces (30,35), with equation 1 as follows:where K is the die-off rate coefficient (dimensionless) and y 0 and y t are the oocyst numbers at time zero, under the initial condition, and at time t (any suitable unit of time), respectively. If normalized by the initial oocyst number, equation 1 can be rewritten as follows:whereIn equation 2, K is independent of the initial oocyst number and represents a constant die-off rate over the entire incubation period. Alternatively, for a given percentage of inactivated oocysts, K is inversely proportional to the incubation time. By using equation 2, it is possible to estimate the infectivity of oocysts at a given time. For example, if K is 0.01 day Ϫ1 , the inactivation of 99.9% of oocysts requires 690 days, compared to 138 days when K is 0.05 day Ϫ1 . In addition, it is possible to find relationships between K and other quantifiable environmental factors.King and Monis (26) reviewed many critical environmental factors affecting Cryptosporidium oocyst survival, ranging from the abiotic stresses of temperature, pH, ammonia, salinity, desiccation, and solar radiation to biotic antagonism. Oocyst survival in soils and feces has received less attention than that in water, perhaps because more complicated stresses occur in terrestrial than in aquatic environments. Aside from the temperature, moisture level (or soil water potential), mineralogy, pH, and presence and composition of organic matter, other physical, chemical, and biological properties may play a potential role in the infectivity of oocysts in soils (9,20,24,28,37). Additional stresses such as the composition of manure, the concentration of ammonia, and pile style may also influence oocyst fate in feces and slurry spread on land (19,22,35). Therefore, in any environment, multiple concomitant factors such as those aforementioned c...

Significance of Wall Structure, Macromolecular Composition, and Surface Polymers to the Survival and Transport of Cryptosporidium parvum Oocysts

“…Low temperatures above freezing extend oocyst viability and infectivity for very long times (12,18,19,20,35). Environmental temperature is a major factor controlling oocyst survival (23,24,32). While there have been many studies documenting the significance of temperature for oocyst survival and the influence of temperature on stored energy reserve utilization has been recognized (see references 10 and 32 for reviews), the effects of temperature on the key oocyst wall structures and macromolecules have not been well investigated.…”

Evaluation of the Solar Water Disinfection Process (SODIS) Against Cryptosporidium parvum Using a 25-L Static Solar Reactor Fitted with a Compound Parabolic Collector (CPC)

“…5 During the tests, the temperature in the interior of the reactor was registered every 1 hour, because this temperature is also a critical factor to determine the survival of the infective forms of C. parvum in the environment. 32 Thus, the maximum temperatures were reached in the most turbid water samples (30 NTU), reaching as high as 57 C during the last 2 hours of the assay. In addition, in previous SODIS studies also carried out under field conditions, the phenomenon of spontaneous excystation was observed.…”

Thermal Contribution to the Inactivation of Cryptosporidium in Plastic Bottles during Solar Water Disinfection Procedures

“…In a recent review of the effect of temperature on the die-off rate for C. parvum oocysts in water, soil, and feces, 28 the authors concluded that temperature may be the most lethal factor for Cryptosporidium in the environment. The studies included in this review were classified into those in which freezing conditions were tested, others in which temperature between 0°C and 37°C were assayed, and those in which temperatures greater than 45°C were used, with exposure times between one and several minutes for high temperatures 29 and weeks and even months for freezing and environmental temperatures.…”