Study of the combined influence of environmental factors on viability of cryptosporidium parvum oocysts in water evaluated by fluorogenic vital dyes and excystation techniques.

Using a factorial experimental design, the combined effect of salinity, temperature and storage time on the viability of Cryptosporidium parvum oocysts in water was evaluated by fluorogenic vital dyes (4',6-diamidino-2-phenylindole and propidium iodide) and an excystation technique. Salinity, storage time and their interaction seemed to be the most influential factors, whereas temperature was not a significant factor. Under unfavourable conditions (salinity 35 per thousand, storage time 40 days), even more than 20% of oocysts remain viable, indicating a high risk of infection for immunocompromised individuals.