VIABILITY AND INFECTIVITY OF CRYPTOSPORIDIUM-PARVUM OOCYSTS ARE RETAINED UPON INTESTINAL PASSAGE THROUGH A REFRACTORY AVIAN HOST

Six Cryptosporidium-free Peking ducks (Anas platyrhynchos) were each o rally inoculated with 2.0 x 10(6) Cryptosporidium parvum oocysts infec tious to neonatal BALB/c mice, Histological examination of the stomach s jejunums, ilea, ceca, cloacae, larynges, tracheae, and lungs of the ducks euthanized on day 7 postinoculation (p.i.) revealed no life-cycl e stages of C. parvum, However, inoculum-derived oocysts extracted fro m duck feces established severe infection in eight neonatal BALB/c mic e (inoculum dose, 2,5 x 10(5) per mouse), On the basis of acid-fast st ained direct wet smears, 73% of the oocysts in duck feces were intact (27% were oocyst shells), and their morphological features conformed t o those of viable and infectious oocysts of the original inoculum, The fluorescence scores of the inoculated oocysts, obtained by use of the MERIFLUOR test, were identical to those obtained for the feces-recove red oocysts (the majority were 3+ to 4+), The dynamics of oocyst shedd ing showed that the birds released a significantly higher number of in tact oocysts than the oocyst shells (P < 0.01), The number of intact o ocysts shed (87%) during the first 2 days p.i. was significantly highe r than the number shed during the remaining 5 days p.i. (P < 0.01) and significantly decreased from day 1 to day 2 p.i. (P < 0.01), The numb er of oocyst shells shed during 7 days p.i. did not vary significantly (P > 0.05), The retention of infectivity of C. parvum oocysts after i ntestinal passage through an aquatic bird has serious epidemiological and epizootiological implications. Waterfowl may serve as mechanical v ectors for the waterborne oocysts and may enhance contamination of sur face waters with C. parvum. As the concentration of Cryptosporidium oo cysts in source waters is attributable to watershed management practic es, the watershed protection program should consider waterfowl as a po tential factor enhancing contamination of the source water with C. par vum.