Pattern of Cryptosporidium parvum oocyst excretion by experimentally infected dogs.

Six 6-week-old Beagle dogs were fed Cryptosporidium parvum oocysts of calf origin. All 6 dogs shed oocysts in faeces. Greater numbers of oocysts were detected with a Weber concentration technique (formalin-ethyl acetate extraction and NaCl centrifugal flotation) stained with either fluorescent antibody or modified Ziehl-Neelsen than with other formalin-ether or -ethyl acetate extraction methods. Oocyst numbers g-1 of faeces rose from days 3 to 5 to a first and highest peak lasting to days 7-9, and 5 of the 6 dogs passed oocysts for at least 80 days. However, the numbers of oocysts detected in the dogs' faeces were low, only 16.1% of the samples in the first month after infection and 2.5% thereafter contained > or = 10000 oocysts g-1 of faeces. Oocyst production was cyclical, with 19.3% of samples negative in the first month after infection and 42.5% thereafter.