Influence of Temperature on Cryptosporidium parvum Oocyst Infectivity in River Water Samples as Detected by Tissue Culture Assay

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...

Section: Oocyst Survival In Watermentioning

confidence: 51%

Section: Oocyst Survival In Watermentioning

confidence: 99%

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

Peng

Murphy²,

Holden

2008

“…The use of U.S. EPA method 1623 for detection of Crypto- (27) has been utilized in a number of studies (11,15,21,22,(26)(27)(28)34), and results coincide well with those of mouse infectivity assays (15). Approximately one-quarter of the disinfected effluent samples with detected Cryptosporidium oocysts had detectable levels of infectious Cryptosporidium, a disturbing observation in that reclaimed water represents a potential human exposure pathway, depending on how the reclaimed water is used.…”

Section: Discussionmentioning

confidence: 99%

Validity of the Indicator Organism Paradigm for Pathogen Reduction in Reclaimed Water and Public Health Protection

Harwood

Levine

Scott

et al. 2005

479

280

The validity of using indicator organisms (total and fecal coliforms, enterococci, Clostridium perfringens, and F-specific coliphages) to predict the presence or absence of pathogens (infectious enteric viruses, Cryptosporidium, and Giardia) was tested at six wastewater reclamation facilities. Multiple samplings conducted at each facility over a 1-year period. Larger sample volumes for indicators (0.2 to 0.4 liters) and pathogens (30 to 100 liters) resulted in more sensitive detection limits than are typical of routine monitoring. Microorganisms were detected in disinfected effluent samples at the following frequencies: total coliforms, 63%; fecal coliforms, 27%; enterococci, 27%; C. perfringens, 61%; F-specific coliphages, ϳ40%; and enteric viruses, 31%. Cryptosporidium oocysts and Giardia cysts were detected in 70% and 80%, respectively, of reclaimed water samples. Viable Cryptosporidium, based on cell culture infectivity assays, was detected in 20% of the reclaimed water samples. No strong correlation was found for any indicator-pathogen combination. When data for all indicators were tested using discriminant analysis, the presence/absence patterns for Giardia cysts, Cryptosporidium oocysts, infectious Cryptosporidium, and infectious enteric viruses were predicted for over 71% of disinfected effluents. The failure of measurements of single indicator organism to correlate with pathogens suggests that public health is not adequately protected by simple monitoring schemes based on detection of a single indicator, particularly at the detection limits routinely employed. Monitoring a suite of indicator organisms in reclaimed effluent is more likely to be predictive of the presence of certain pathogens, and a need for additional pathogen monitoring in reclaimed water in order to protect public health is suggested by this study.

“…While the effects of some abiotic ecological determinants on protozoa in surface water systems have been identified (8,9,3,4), very little work has addressed the biotic effects of cohabitating freshwater zooplankton as grazers of these pathogens. Prior studies have shown that protozoa can ingest human bacterial and protozoan pathogens, including Cryptosporidium (1,16,18).…”

mentioning

confidence: 99%

Impact of Zooplankton Grazing on the Excystation, Viability, and Infectivity of the Protozoan Pathogens Cryptosporidium parvum and Giardia lamblia

Connelly

Wolyniak

Dieter

et al. 2007

Very little is known about the ability of the zooplankton grazer Daphnia pulicaria to reduce populations of Giardia lamblia cysts and Cryptosporidium parvum oocysts in surface waters. The potential for D. pulicaria to act as a biological filter of C. parvum and G. lamblia was tested under three grazing pressures (one, two, or four D. pulicaria grazers per 66 ml). (Oo)cysts (1 ؋ 10 4 per 66 ml) were added to each grazing bottle along with the algal food Selenastrum capricornutum (6.6 ؋ 10 4 cells per 66 ml) to stimulate normal grazing. Bottles were rotated (2 rpm) to prevent settling of (oo)cysts and algae for 24 h (a light:dark cycle of 16 h:8 h) at 20°C. The impact of D. pulicaria grazing on (oo)cysts was assessed by (i) (oo)cyst clearance rates, (ii) (oo)cyst viability, (iii) (oo)cyst excystation, and (iv) oocyst infectivity in cell culture. Two D. pulicaria grazers significantly decreased the total number of C. parvum oocysts by 52% and G. lamblia cysts by 44%. Furthermore, two D. pulicaria grazers significantly decreased C. parvum excystation and infectivity by 5% and 87%, respectively. Two D. pulicaria grazers significantly decreased the viability of G. lamblia cysts by 52%, but analysis of G. lamblia excystation was confounded by observed mechanical disruption of the cysts after grazing. No mechanical disruption of the C. parvum oocysts was observed, presumably due to their smaller size. The data provide strong evidence that zooplankton grazers have the potential to substantially decrease the population of infectious C. parvum and G. lamblia in freshwater ecosystems.