The survival of Sarcocystis gigantea sporocysts following exposure to various chemical and physical agents.

Using in vitro excystation as a measure of viability, it was found that at 4 degrees C Sarcocystis gigantea sporocysts survived considerably better in tap water (85% excystation after 174 days) than in either 2.5% potassium dichromate (15% excystation after 174 days) or 2% sulphuric acid (0% excystation after 5 days). Although they were able to resist 48 h suspension at room temperature in most laboratory reagents and disinfectants tested, six (sulphuric acid, ammonia, methanol, ethanol, potassium hydroxide, sodium hydroxide, Medol) had substantial sporocysticidal properties. Further investigation with three of these showed that sporocyst excystation was reduced from 65% to less than 10% following contact with 2.5% sulphuric acid for 1 h or with 2% ammonia or 4% Medol for 4 h. Sporocysts were either killed or had their ability to excyst severely impaired by heating to 60 degrees C and 55 degrees C for 5 and 60 min, respectively, by exposure to ultraviolet radiation at a dose of 4000 ET, or by prolonged storage in water at 24 degrees C. Sporocysts exposed to either constant or intermittent freezing at -18 degrees C suffered a comparatively slow decline in excystation rate with time, as did those subjected to desiccation. The duration of survival of desiccated sporocysts was inversely related to relative humidity and after 245 days at 33% relative humidity and temperatures of 15 degrees C or 24 degrees C, 60% of such sporocysts excysted.