INFECTIVITY OF CRYPTOSPORIDIUM-PARVUM OOCYSTS IS RETAINED UPON INTESTINAL PASSAGE THROUGH A MIGRATORY WATER-FOWL SPECIES (CANADA GOOSE, BRANTA-CANADENSIS)

Five Cryptosporidium-free Canada geese (Branta canadensis) were indivi dually orally dosed with 3.5 x 10(6) Cryptosporidium parvum oocysts in fectious to neonatal BALB/c mice. After intestinal passage, inoculum-d erived oocysts extracted from goose faeces established severe infectio n in 14 neonatal BALB/c mice (inoculum dose 2.5 x 10(5)/mouse). The in oculum-derived oocysts were detected in goose faeces up to 9 days post -inoculation (PI); the number of intact oocysts and oocyst shells shed during the first 3 days PI was significantly higher than for the rema ining 6 days PI (P<0.01). Based on acid-fast stained air-dried direct wet smears, 62% of the oocysts in goose faeces were intact (oocyst she lls constituted 38%) and conformed to morphological features of viable and infectious inoculum oocysts. The fluorescence scores of the inocu lated oocysts, obtained by use of the MERIFLUOR test, were identical t o those obtained for the faeces-recovered oocysts (majority 3+ to 4+) The dynamics of oocyst shedding showed that overall, the birds release d a significantly higher number of intact oocysts than oocyst shells ( P<0.01). Retention of the viability and infectivity of C. parvum oocys ts following intestinal passage through a migratory water-fowl species has serious epidemiological implications. Water-fowl can serve as mec hanical vectors for the water-borne oocysts and can contaminate surfac e waters with C. parvum. As the concentration of Cryptosporidium oocys ts in source waters is attributable to water-shed management practices , water-shed protection programme officials should consider water-fowl as a potential factor enhancing contamination of the source water wit h Cryptosporidium.