Submitted to: Parasitology Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/11/2002
Publication Date: 12/1/2002
Citation: Jenkins, M.C., Trout, J.M., Higgins, J.A., Dorsch, M., Veal, D., Fayer, R. 2002. Comparison of assays for viable Cryptosporidium parvum oocysts stored in water at constant temperature. Parasitology Research. Vol. 89:1-5. Interpretive Summary: Cryptosporidiosis is a diarrheal disease that causes significant morbidity and mortality in humans and cattle. The causative organism is protozoan parasite, namely Cryptosporidium parvum, which is resistant to most disinfectants that are used in the home and in water treatment plants. Also, there are no known drugs to treat persons infected with C. parvum. The oocyst stage of the parasite is also well adapted to surviving in the environment for long periods of time, due in part to the rigid outer covering that surrounds the infectious stage of the organism. The purpose of this study was to determine how long C. parvum oocysts would remain viable in water at a modest temperature of 15 degrees C. Oocysts were removed from a water bath each month and tested in a variety of infection and viability assays. This study showed that C. parvum oocysts remained viable up to 7 months at this temperature. After 7 months, the parasite was no longer viable. These results provide further evidence of the hardiness of C. parvum oocysts in water and that the parasite can remain infectious for long periods of time after a contamination event occurs.
Technical Abstract: Cryptosporidium parvum oocysts were stored in sterile water for 9 months at 15 degrees C. A sample was removed monthly and subjected to a variety of assays to determine oocyst viability. Mouse infection and cell culture showed that C. parvum oocysts remained viable when stored for 7 months at this temperature. Fluorescence in -situ hybridization (FISH) using probes directed to ribosomal RNA was also applied to these oocysts. The proportion of FISH positive oocysts was 70-80% for the first 2 months of storage, decreased and remained nearly constant at 40-50% between 3 to 7 months, decreased to 20% by 8 months, and to 0% by 9 months. The storage carbohydrate, amylopectin, and the presence of mRNA for amyloglucosidase (CPAG) as measured by RT-PCR decreased much more rapidly. By 3 months and for the remainder of the incubation period, amylopectin content was 20% of the original amount present in the oocysts. The CPAG RT-PCR signal at 3 months was 50% of that observed after 1 month storage, 20% at 4 months, an was not detected thereafter.