Submitted to: Journal of Parasitology
Publication Type: Research Notes
Publication Acceptance Date: December 1, 2003
Publication Date: June 1, 2004
Citation: Fayer, R. 2004. Infectivity of microsporidia spores stored in seawater at environmental temperatures. Journal of Parasitology. 90:654-657.
Interpretive Summary: Fourteen species of microsporidian parasites infect humans. Of these, Encephalitozoon cuniculi, Encephalitozoon hellem, and Encephalitozoon intestinalis are zoonotic, infecting domesticated animals and wildlife. Although the actual routes of transmission are not known, it is possible that the infectious spore stage in urine or feces can contaminate surface waters used for recreation or drinking water. Spores have been detected by microscopic and molecular methods in surface waters, but only circumstantial evidence of waterborne transmission is available. Under experimental conditions spores of these species stored in water at environmental temperatures remained infectious long enough to become widely dispersed in the environment. However, nothing was known of how long these spores can remain infectious in seawater. In the present study it was found that, based strictly on salinity and temperature, spores could potentially remain infectious long enough to become widely dispersed in estuarine and coastal waters used for recreation and shellfish harvesting. Knowledge of the affect of salinity and temperature on infectivity of microsporidia in seawater is necessary for evaluating the risk of waterborne contamination.
To determine how long spores of Encephalitozoon cuniculi, E. hellem, and E. intestinalis remain viable in seawater at environmental temperatures, culture-derived spores were stored in 10, 20, and 30 ppt artificial seawater at 10 and 20 C. At intervals of 1, 2, 4, 8, and 12 wk spores were tested for infectivity in monolayer cultures of MDBK cells. Spores of E. hellem appeared the most robust, some remaining infectious in 30 ppt seawater at 10 C for 12 wk and at 30 ppt seawater at 20 C for 2 wk. Those of E. intestinalis were slightly less robust, remaining infectious at 30 ppt seawater at 10 and 20 C for 1 and 2 wk, respectively. Spores of E. cuniculi remained infectious at 10 ppt at 10 and 20 C for 2 wk but not at higher salinities. These findings indicate that spores of three species of Encephalitozoon vary in their ability to remain viable when exposed to a conservative range of salinities and temperatures found in nature but, based strictly on salinity and temperature, can potentially remain infectious long enough to become widely dispersed in estuarine and coastal waters.