Comparative reproduction of Cryptosporidium baileyi in embryonated eggs and in chickens.

At 2 days of age, each of 20 chickens was perorally or intracloacally infected with 3 x 10(5) oocysts of Cryptosporidium baileyi and maintained for 13 days post infection. In parallel, 20 embryonated chicken eggs were inoculated with 3 x 10(5) oocysts at day 10 of embryonation and were incubated for a further 7 days. The average reproduction rates in the two groups of chickens were x560 after peroral infection and x533 after intracloacal infection as compared with x256 in the eggs. Although the rate of reproduction of parasites seen in the eggs was only about 50% of that observed in chickens, large numbers of oocysts could be harvested (on average, 77 million per egg versus 161 and 168 million from chickens). Nearly the same number of oocysts could be obtained from two eggs as compared with one chicken. The use of embryonated eggs accommodates the sense of animal-protection regulations, is less expensive, and allows the isolation of oocysts under sterile conditions.