Efficacy of UV Irradiation in Inactivating Cryptosporidium parvum Oocysts

Abstract

To evaluate the effectiveness of UV irradiation in inactivating Cryptosporidium parvum oocysts, the animal infectivities and excystation abilities of oocysts that had been exposed to various UV doses were determined. Infectivity decreased exponentially as the UV dose increased, and the required dose for a 2-log 10 reduction in infectivity (99% inactivation) was approximately 1.0 mWs/cm 2 at 20°C. However, C. parvum oocysts exhibited high resistance to UV irradiation, requiring an extremely high dose of 230 mWs/cm 2 for a 2-log 10 reduction in excystation, which was used to assess viability. Moreover, the excystation ability exhibited only slight decreases at UV doses below 100 mWs/cm 2 . Thus, UV treatment resulted in oocysts that were able to excyst but not infect. The effects of temperature and UV intensity on the UV dose requirement were also studied. The results showed that for every 10°C reduction in water temperature, the increase in the UV irradiation dose required for a 2-log 10 reduction in infectivity was only 7%, and for every 10-fold increase in intensity, the dose increase was only 8%. In addition, the potential of oocysts to recover infectivity and to repair UV-induced injury (pyrimidine dimers) in DNA by photoreactivation and dark repair was investigated. There was no recovery in infectivity following treatment by fluorescent-light irradiation or storage in darkness. In contrast, UV-induced pyrimidine dimers in the DNA were apparently repaired by both photoreactivation and dark repair, as determined by endonuclease-sensitive site assay. However, the recovery rate was different in each process. Given these results, the effects of UV irradiation on C. parvum oocysts as determined by animal infectivity can conclusively be considered irreversible.

Evaluation of a Small Scale UV-treated Recirculating Depuration System for Oysters (<i>Crassostrea iredalei</i>)

“…Depuration using UV light is usually effective provided that the water flow rate is adequate to its capacity [15]. UV disinfection technology can be readily applied, is low maintenance, results in significant viability reductions of all waterborne pathogens, and produces no hazardous by-products [16,17]. UV radiation eliminates enteric bacteria, viruses, bacterial and protozoan spores in the water without the production of toxic by-products or other chemical residues [13].…”

Inactivation of Enteric Adenovirus and Feline Calicivirus by Chlorine Dioxide

“…While chlorine is the most common disinfectant in the United States for drinking water and wastewater treatment, alternative disinfectants are needed to reduce highly chlorine resistant pathogens, such as Cryptosporidium parvum. UV light disinfection is effective at reducing Cryptosporidium oocysts (6,34), and it is therefore an attractive alternative disinfectant to chlorine for drinking water treatment. Recent evidence, however, has shown that UV light is ineffective at reducing enteric adenovirus at doses commonly applied by water treatment systems (45).…”

Low- or Medium-pressure UV Lamp Inactivation of Microcystis aeruginosa

“…The molecular lengths of fragmented DNA are determined by alkaline agarose gel electrophoresis, followed by a theoretical calculation to obtain the number of ESS (14). This assay was applied in the survey of UV-irradiated health-related microbes such as Escherichia coli, Cryptosporidium parvum and Legionella pneumophila (15,16,17,18). The conditions for the ESS assay used in this study were basically the same as those described previously (15).…”