Resistance of Cryptosporidium parvum oocysts following commercial bleach treatment / 대한수의학회지

We investigate the resistance of Cryptosporidium (C.) parvum oocysts to commercial bleach treatment. The viability and infectivity of C. parvum oocysts suspended in 100, 50, 25, 12.5, 6.3 or 3.2% aqueous commercial bleach for 10, 30, 60, 120 or 180 min at room temperature were assessed by nucleic acid Syto-9 staining, histologic examination of ileum and infectivity to immunosuppressed neonatal C57BL/6N mice. Although the viability was decreased compared with normal oocysts, all oocysts in contact with serially diluted commercial bleach for 180 min were alive by nucleic acid dye Syto-9 staining. And, microscopic examination of ileum sections revealed developmental stages of C. parvum in all mice. The oocyst shedding patterns between mice infected with oocysts contacted with commercial bleach and normal control mice were not significantly different each other. Although commercial bleach is widely used as a bacterial and viral disinfectant, the present findings indicate that it is not an effective disinfectant for C. parvum oocysts under practical conditions. Authors conclude that, therefore, it is undesirable to recommend commercial bleach as a disinfectant for C. parvum oocysts.

Concurrent response to challenge infection with Cryptosporidium parvum in immunosuppressed C57BL/6N mice

We investigated the response to challenge infection with Cryptosporidium parvum oocysts in immunosuppressed C57BL/6N mice. In the primary infection, fecal oocyst shedding and parasite colonization were greater in immunosuppressed mice than in nonimmunosuppressed mice. Compared with primary infection, challenge infection with C. parvum didn't show any oocyst shedding and parasite colonization. Especially, oocyst shedding and parasite colonization from the mice infected with heatkilled oocysts were not detected. After challenge infection with C. parvum oocysts, however, these mice were shedding small numbers of oocysts and parasite colonization. Except normal control and uninfected groups, the antibody titers of other groups appear similar. Based on the fecal oocyst shedding, parasite colonization of ilea, and antibody titers in the mice, these results suggest that the resistance to challenge infection with C. parvum in immunosuppressed C57BL/6N mice has increased.

Viability of preserved Cryptosporidium baileyi oocysts

The present study was undertaken to determine the viability and infectivity of oocysts of Cryptosporidium baileyi that had been stored from 1 to 40 months at 4 degrees C preserved in 2.5% potassium dichromate solution. Oocysts of C. baileyi were purified from the feces of experimentally infected chickens using discontinuous sucrose gradients. Subsequently, the purified oocysts were suspended in 2.5% potassium dichromate solution at a concentration of 1 x 10 (7) organism/ml, and their viabilities were assessed by nucleic acid staining, histologic examination, and infectivity to 2-day-old chickens. All chickens inoculated with oocysts that had been stored for 1-18 months developed patent infections, while chickens infected with older oocysts remained uninfected. Between 5.8% and 82.2% of the oocysts, stored at 4 degrees C in 2.5% potassium dichromate solution, were found to be viable, as determined by nucleic acid staining. Parasite colonization in the bursa of Fabricius was detected in the microvillus border of bursal epithelium. The finding that C. baileyi oocysts remain infective to chickens for at least 18 months offers important time-saving advantages to investigators who frequently require large numbers of oocysts.