Artificial UV-B and Solar Radiation Reduce in Vitro Infectivity of the Human Pathogen Cryptosporidium parvum

Abstract

The potential for solar ultraviolet (UV) radiation to act as a significant abiotic control of Cryptosporidium parvum oocysts in nature is unknown. Infectivity of C. parvum following exposure to artificial UV-B and natural solar radiation, with and without UV wavelengths, was tested under controlled pH and temperature conditions. Percent infectivity of exposed oocysts was determined by in vitro cell culture. Artificial UV-B exposures of 32 and 66 kJ/m2 significantly decreased oocyst infectivity by an average of 58 and 98%, respectively. Exposure of oocysts to approximately half and full intensity of full solar spectrum (all wavelengths) for a period of less than 1 day (10 h) in mid-summer reduced mean infectivity by an average of 67% and >99.99%, respectively. Exposure of the C. parvum oocysts to UV-shielded solar radiation (>404 nm) in early autumn reduced mean infectivity by 52%, while full spectrum solar radiation (exposure at all wavelengths) reduced mean infectivity by 97%. The data provide strong evidence that exposure to natural solar radiation can significantly reduce C. parvum infectivity. Direct effects of solar radiation on oocysts in nature will depend on the depth distribution of the oocysts, water transparency, mixing conditions, and perhaps other environmental factors such as temperature, pH, and stress.

Biofilms Reduce Solar Disinfection of Cryptosporidium parvum Oocysts

“…1). These data support the observations of others that solar radiation reduces oocyst infectivity (6,11,15); however, approximately 20% of the oocysts exposed to the highest levels of solar radiation remained infectious and a potential public health threat.…”

“…Despite various lengths of exposure time (90, 50, and 60 min for the July 9, July 15, and August 25 experiments, respectively), sky conditions resulted in all three experiments having similar solar exposure (0.37, 0.28, and 0.23 exposure days, respectively) ( Table 1), and these exposures were comparable to those in previous experiments (6) (0.33 to 0.38 exposure days), in which infectivity was reduced to 0 to 6% of the stock infectivity (compared to 16 to 20% in these experiments). Differences in infectivity reductions may result from the greater attenuation of radiation by the glass-covered flow chambers used here compared to the quartz dishes used previously (6), variation in oocyst lots (26), and overnight oocyst storage before infectivity processing (6).…”

“…Artificial UV radiation has irreversible effects on oocyst infectivity (5,8,11,12,16,23,33) but can be cost-prohibitive, so the use of natural solar radiation to inactivate oocysts is worth investigating. Solar radiation (UV and non-UV wavelengths) has been shown through cell culture infectivity to effectively disinfect C. parvum (6).…”

Ultraviolet Insights: Attempting to Resolve Enigmatic Patterns in Pelagic Freshwaters – The Historical Context and a View to the Future

“…Artificial UV radiation has also been used to sterilize drinking water supplies by inactivating pathogens (WOLFE, 1990) and degrading pollutants (LEGRINI et al, 1993). Natural solar UV radiation can also significantly reduce the infectivity of pathogens like Cryptosporidium parvum (CONNELLY et al, 2007) as well as degrade contaminants such as PAHs (LEE, 2003). DOM can reduce phototoxicity by selectively absorbing UV (BARRON et al, 2000;DIA-MOND et al, 2000) or by binding toxic compounds (ORIS et al, 1990;WEINSTEIN and ORIS, 1999).…”

Inactivation of MS2 Phage and Cryptosporidium parvum Oocysts Using UV-A from High-Intensity Light-Emitting Diode for Water Disinfection

“…Male-specific-2 bacteriophage (MS2) has been used as a model organism for Cryptosporidium, Giardia, and intestinal viruses to test the inactivation by UV-C (Havelaar et al, 1993;US EPA 2006). Although a few studies have reported the use of sunlight (Connelly et al, 2007;Kohn and Nelson 2007;King et al, 2008;Gomez-Couso et al, 2009), most UV disinfection studies have used a low-or medium-pressure mercury lamp at a wavelength of around 254 nm (near the peak wavelength of DNA absorbance: UV-C range).…”