Survival of Cryptosporidium parvum oocysts after prolonged exposure to still natural mineral waters

Abstract

The survival kinetics of purified Cryptosporidium parvum oocysts of both human and ovine origin, immersed in four still natural mineral waters (total dissolved salts ranging from 91 mg/liter to 430 mg/liter) and reverse osmosis water was assessed by inclusion or exclusion of the fluorogenic vital dyes 4′,6-diamidino-2-phenylindole and propidium iodide over a 12-week period. Semipermeable chambers were used to contain the oocysts while immersed in each mineral water type, permitting both intimate interactions between oocysts and matrices and straightforward sampling for viability assessments. The viability of both oocyst types, assessed at weekly intervals, remained unaltered after 12 weeks at 4°C, whereas a progressive decline in the viability of both oocyst isolates was observed when immersed in mineral waters at 20°C. At 20°C, approximately 30% of oocysts remained viable after 12 weeks incubation. Here, temperature was the major factor that adversely affected oocyst survival, although higher mineral content was also proportionally and significantly associated with this increased oocyst inactivation. The prolonged survival of oocysts at 4°C in our studies indicates that they could survive for prolonged periods of time in U.K. groundwaters (average temperature ∼10°C) and thus represent a potential public health hazard if contamination of mineral water sources by viable oocysts were to occur.