Seasonal change of Cryptosporidium and Giardia distribution in a tropical Chao Phraya river ,Thailand

摘要

Cryptosporidium and Giardia are the major causative waterborn protozoan of gastroenteritis in humans and represent a significant threat to public health. This study intends to evaluate the protozoa distribution in Chao Phraya river, a major drinking water source in Thailand and its seasonality in prevalence. A total of 114 water samples were collected during three consecutive seasons over a 1-year period and analyzed according to USEPA method 1623 to detect Cryptosporidium oocysts and Giardia cysts. Overall, 67.5 % of the samples were positive for at least one of the protozoan, while Cryptosporidium and Giardia were found in 63.2% and 48.2% respectively, with occasional high concentration peaks. A significant seasonal pattern was observed, with positive samples for Cryptosporidium more frequent in rainy and cold than summer, and positive samples for Giardia less frequent in summer. The parasite density and rainfalls were significantly associated with Cryptosporidium concentration but not Giardia. Downstream portion of the river seems to contribute mainly to the parasitic contamination observed in upstream.The study indicated that Cryptosporidium and Giardia are consistently found at elevated concentrations in these waters for human consumption, thereby involve significant public health risks. Based on seasonal pattern and rainfall correlation, the possible origin of contamination is due to agricultural practices and dysfunction of sewage treatment plants during periods of heavy rainfalls. It is likely that the climate changes increased the number of (oo)cysts which facilitated transmission and pose a threat with potential hazards for the public health. Such information is critical to determine the significant of , and develop appropriate regulation for, waterborn parasites.