Total and infectious Cryptosporidium oocyst and total Giardia cyst concentrations from distinct agricultural and urban contamination sources in Eastern Canada

Abstract

Cryptosporidium and Giardia (oo)cyst concentrations are frequently used for assessing drinking water safety. The widely used USEPA Method 1623 provides total counts of (oo)cysts, but may not be accurate for human health risk characterization, since it does not provide infectivity information. The total counts and infectious fraction of Cryptosporidium oocysts and the total counts of Giardia cysts were assessed in major fecal pollution sources. Fresh calf and cow feces, their manure, and the discharge point were sampled in a small rural sub-watershed (n ¼ 20, 21, 10, 10). Median concentrations for total (oo)cysts were higher in calves (333 oocysts g À1 ; 111 cysts g À1 ) than in cows (52 oocysts g À1 ; 7 cysts g À1 ). Infectious oocysts were found in 17 (7%) of the samples and none were found in manure or at the discharge point. Urban sources were sampled in the influent and effluent (n ¼ 19, 18) of two wastewater treatment plants. Peak concentrations were 533 oocysts L À1 and 9,010 cysts L À1 for influents and 89 oocysts L À1 and 472 cysts L À1 for effluents. Infectious oocyst fractions varied from below the detection limit to 7-22% in the effluent and influent respectively.These infectious fractions are significantly lower than those currently used for quantitative microbial risk assessment estimates.

Integrated Cryptosporidium Assay To Determine Oocyst Density, Infectivity, and Genotype for Risk Assessment of Source and Reuse Water

“…However, no infectious oocysts were detected in the effluent after UV disinfection, representing an inactivation of greater than 3.24 log 10 . Combination of removal and inactivation data for plant B resulted in an overall reduction of Ͼ4.36 log 10 .…”

“…To address this, we modified a highly sensitive infectivity assay capable of detecting a single infectious oocyst (14), converting the assay format from a Labtek slide culture system to a plate-based assay and developing a simple DNA extraction method to allow PCR-based identification of any infectious foci. This modified assay further built upon the work of Lalancette et al (10,13), incorporating a variety of oocyst recovery controls to allow estimates of the number of oocysts applied to cell culture for determination of infectivity ratios and of the number of oocysts in the original water sample. This new assay was evaluated using a variety of water matrices.…”

“…Cryptosporidium species are commonly monitored in waters using standard detection methodologies (e.g., EPA Method 1622 and Method 1623). However, these methods provide no information on either the infectivity or identity of the detected oocyst, providing little information on the relative health risk posed to humans (9,10).…”

“…Recently, intensive efforts have been made to examine source waters destined for potable consumption, as well as wastewaters intended for reuse, using genotyping assays and, to a lesser extent, infectivity assays (9)(10)(11)(12)(13). The information from these assays provides an indication of the risk to of human health (13).…”

“…To address a number of these shortcomings, Lalancette and colleagues developed a dual-direct-detection assay to provide information on the fraction of infectious oocysts from a water sample (10,13). To achieve this, they combined a cell culture immunofluorescence infectivity assay with a direct count of oocysts on the host cell monolayer as well as from washes off the monolayer using a filtration technique to capture oocysts.…”