Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/28/1994
Publication Date: N/A
Interpretive Summary: Cryptosporidium parvum is widespread waterborne protozoan parasite infectious for virtually all mammals including humans. The infectious stage, the oocyst, is shed in the feces of the infected host, contaminating the environment and serving as a source of infection for others. The oocyst, extremely resistant to chemical disinfectants, was tested for its ability to withstand elevated temperatures and remain infectious. Utilizing laboratory mice as recipients of oocysts exposed to temperatures ranging from 60 to 100 C at 5 degree increments for 1 and 5 minute periods, a temperature vs time inactivation chart was developed. Oocysts were rendered noninfectious at 71.1 C and higher for 1 minute and at 60 C or higher for 5 minutes. This information will be extremely helpful to public health agencies and others concerned with disinfecting contaminated drinking water
Technical Abstract: Cryptosporidium parvum (Cp) oocyst suspended in 0.5 ml distilled water were pipetted into plastic vials which were inserted into wells in the heated metal block of a thermal DNA cycler. Block temperatures were set at 5 degree incremental temperatures from 60 to 100 C. At each temperature setting 4 vials containing Cp oocysts were placed into wells, held for 15 sec before time was recorded as zero, and then pairs of vials were removed 1 min and 5 min later. Upon removal, all were immediately cooled on crushed ice. Also at each temperature interval 1 vial containing 0.5 ml of distilled water was placed in a well and a digital thermometer was used to record the actual water temperature at 30 sec intervals. Heated oocyst suspensions as well as unheated control suspensions were orally inoculated by gavage into 7- to 10-day old BALB/c mouse pups to test for infectivity. At 96 hr after inoculation the ileum, cecum, and colon from each mouse was removed and prepared for histology. Tissue sections were examined microscopically. Developmental stages of Cp were found in all 3 segments of gut from all mice that received oocysts in unheated water and in water that reached temperatures of 53, 59, and 66 C at 1 min when vials were removed from the heat source. Cp was also found in the ileum of 1 of 6 mice that received oocysts in water that reached a temperature of 58.7 C at 5 min. These data indicated that when water containing Cp oocysts reached temperatures of 71.1 C or higher within 1 min or when the temperature was held at 63.0 C or higher for 2.5 min or longer infectivity was lost.