Cell culture-Taqman PCR assay for evaluation of Cryptosporidium parvum disinfection

Cryptosporidium parvum represents a challenge to the water industry and a threat to public health. In this study, we developed a cell culture-quantitative PCR assay to evaluate the inactivation of C. parvum with disinfectants. The assay was validated by using a range of disinfectants in common use in the water industry, including low-pressure UV light (LP-UV), ozone, mixed oxidants (MIOX), and chlorine. The assay was demonstrated to be reliable and sensitive, with a lower detection limit of a single infectious oocyst. Effective oocyst inactivation was achieved (>2 log(10) units) with LP-UV (20 mJ/cm(2)) or 2 mg of ozone/liter (for 10 min). MIOX and chlorine treatments of oocysts resulted in minimal effective disinfection, with <0.1 log(10) unit being inactivated. These results demonstrate the inability of MIOX to inactivate Cryptosporidium. The assay is a valuable tool for the evaluation of disinfection systems for drinking water and recycled water.

Solar UV reduces Cryptosporidium parvum oocyst infectivity in environmental waters

AIMS

To determine the effect of solar radiation on Cryptosporidium parvum in tap and environmental waters.

METHODS AND RESULTS

Outdoor tank experiments and a cell culture infectivity assay were used to measure solar inactivation of C. parvum oocysts in different waters. Experiments conducted on days with different levels of solar insolation identified rapid inactivation of oocysts in tap water (up to 90% inactivation within the first hour). Increased dissolved organic carbon content in environmental waters decreased solar inactivation. The role of solar ultraviolet (UV) in inactivation was confirmed by long-pass filter experiments, where UV-B was identified as the most germicidal wavelength. Reductions in oocyst infectivity following solar radiation were not related to a loss of excystation capacity.

CONCLUSIONS

Solar UV can rapidly inactivate C. parvum in environmental waters.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study to assess natural sunlight inactivation of C. parvum oocysts in surface waters and drinking water using an infectivity measure and determines the wavelengths of light responsible for the inactivation. The findings presented here provide valuable information for determining the relative risks associated with Cryptosporidium oocysts in aquatic environments and identify solar radiation as a critical process affecting the oocyst survival in the environment.

Bacterial degradation of microcystin toxins in drinking water eliminates their toxicity

Microcystin-LR and -LA were readily biodegraded by a bacterium, Sphingpoyxis sp. LH21, in a treated reservoir water. Detection of the microcystins was conducted using high-performance liquid chromatography (HPLC), protein phosphatase 2A (PP2A) inhibition assay and a cell-based cytotoxicity assay. The HPLC results correlated well with the two assays. The decrease in cytotoxicity, coupled with the associated decrease in microcystin concentrations, indicated that no cytotoxic by-products were being generated, highlighting the applicability of biodegradation as a feasible treatment option for effective microcystin removal.

Cytotoxicity screening for the cyanobacterial toxin cylindrospermopsin

The cell lines C3A, HepG2, NCI-87, HCT-8, HuTu-80, Caco-2, and Vero were screened for sensitivity to the cyanobacterial toxin cylindrospermopsin (CYN), with the aim of determining the most sensitive cells to be used in cytotoxicity tests. Cell lines were chosen to be representative of the organs targeted by the toxin; liver, kidney, intestine, and were expected to have different metabolic activities and uptake capabilities. Over the range of cell lines tested, IC(50) determinations at 24 h (MTT assay) ranged fourfold, from 1.5 muM for hepatocyte-derived cell lines (C3A IC(50) = 1.5 +/- 0.54; HepG2 IC(50) = 1.5 +/- 0.87) to 6.5 +/- 3.3 micro the colon-derived Caco-2 cell line. The cell-line sensitivity seemed to decrease in cell lines derived from progressively more distal regions of the gastrointestinal tract: gastric > duodenal > ileal > colonic. The greater sensitivity of the hepatic cell lines to CYN was also apparent in 7-d exposure studies, with low toxin concentrations exerting cytotoxic effects that were not seen in other cell lines. Short-term exposure of C3A cells to CYN (1-6 h) was shown to induce cytotoxicity at 24 h despite a washout and recovery incubation, demonstrating the protracted and apparently irreversible nature of CYN's toxic effects.

Application of the neuroblastoma assay for paralytic shellfish poisons to neurotoxic freshwater cyanobacteria: interlaboratory calibration and comparison with other methods of analysis

Paralytic shellfish poisons (PSPs) are produced by freshwater cyanobacteria and pose a threat to human and animal drinking-water supplies. The wide range of toxin analogues (and the likelihood that further analogues remain to be discovered) means that chromatographic methods are not always reliable indicators of toxicity. Although the mouse bioassay remains the method of choice in the seafood industry, its use is increasingly being questioned on ethical grounds. The cell-based Neuro-2A neuroblastoma toxicity assay is an alternative bioassay validated for testing shellfish extracts, so it was of interest to determine its applicability with the different suite of toxin analogues produced by cyanobacteria. Cyanobacterial bloom samples from Australia, Brazil, and France were assayed using the neuroblastoma assay, liquid chromatography-tandem mass spectrometry (LC-MS/MS), high-performance liquid chromatography with postcolumn derivatization and fluorescence detection, and the Jellett Rapid Test for PSP. To assess interlaboratory variability, the neuroblastoma assay was set up in laboratories in Paris (France) and Adelaide (Australia). Neuroblastoma and chromatographic methods gave comparable results except in the case of the neurotoxic Brazilian samples: LC-MS/MS did not detect the putative new PSPs contained in these samples. Inter- and intralaboratory variability of the neuroblastoma assay was typical of biological assays but no greater than that found for interassay variability between different chromatographic determinations. The batch of Jellett Rapid Tests for PSP used did not yield quantitative results. Overall, the neuroblastoma assay was useful as a screening assay for determination of toxicity caused by saxitoxin neurotoxins in freshwater cyanobacteria, having the advantage of being sensitive to unidentified toxins that currently cannot be quantified by chromatographic means.

The detection of Japanese encephalitis virus in municipal wastewater during an acute disease outbreak

AIM

To demonstrate the capability of wastewater-based surveillance (WBS) as a tool for detecting potential cases of Japanese Encephalitis Virus (JEV) infection in the community.

METHODS AND RESULTS

In this study, we explore the potential of WBS to detect cases of JEV infection by leveraging from an established SARS-CoV-2 wastewater surveillance program. We describe the use of two reverse transcriptase quantitative polymerase chain reaction (RTqPCR) assays targeting JEV to screen archived samples from two wastewater treatment plants (WWTPs). JEV was detected in wastewater samples collected during a timeframe coinciding with a cluster of acute human encephalitis cases, alongside concurrent evidence of JEV detection in mosquito surveillance and the sentinel chicken programs within South Australia's Riverland and Murraylands regions.

CONCLUSIONS

Current surveillance measures for JEV encounter multiple constraints, which may miss the early stages of JEV circulation or fail to capture the full extent of transmission. The detection of JEV in wastewater during a disease outbreak highlights the potential WBS has as a complementary layer to existing monitoring efforts forming part of the One Health approach required for optimal disease response and control.