Abstract
Mean lengths, widths, and length/width ratios of oocysts of chicken Cryptosporidium sp. isolated in Japan and C. muris were measured during patency and preservation period. The oocysts of Cryptosporidium sp. on days 10, 14 and 20 postinoculation (PI) increased in length by 2-3% from those on day 7, nevertheless, oocyst length/width ratio did not change. The oocysts of C. muris from mice on day 30 PI increased in length by 2-4% from those on day 10 and 14 PI, and former oocysts also increased in length/width ratio. the oocysts of Cryptosporidium sp. on day 10 and C. muris on day 14 were stored in 2% potassium dichromate solution at 4C. they were measured at 3 and 12 months later and compared with oocysts measured at 7 days after preservation. Twelve-month-preserved oocysts from chickens increased in either length and width by 3% and 5-6% from 7-day- and 3-month-preserved oocysts, respectively. The length/width ratio decreased by 2%. In C. muris, twelve-month-preserved oocysts increased in wither width or length/width ratio by 4-5%, though the length was not different. These results suggest that the size of cryptospridian oocysts increased by 2-5% during patency and during preservation.

Key words: oocyst size; Cryptosporidium; classification.