title: Cryptosporidium parvum: determination of ID₅₀ and the dose-response relationship in experimentally challenged dairy calves.
abstract: The objectives were to determine the median infective dose (ID₅₀) of Cryptosporidium parvum and to describe the dose-response relationship including associated clinical illness in experimentally challenged dairy calves. Within the first 24h of life, 27 test calves were experimentally challenged with C. parvum oocysts and 3 control calves were sham dosed. Test calves received 1 of 8 possible doses (25, 50, 100, 500, 1 × 10(3), 1 × 10(4), 1 × 10(5), and 1 × 10(6) oocysts). All 27 test calves developed diarrhea. Fecal oocyst shedding occurred in 25 (92.6%) test calves and in 0 control calves. The 2 non-shedding test calves both received 25 oocysts. There was an inverse relationship between dose and time to onset of fecal oocyst shedding (P=0.005). There was no relationship found between dose and duration (P=0.2) or cessation (P=0.3) of fecal oocyst shedding. In addition, there was not a significant relationship between log-dose and the log-peak oocysts (P=0.2) or log-total oocysts (P=0.5) counted/g of feces across the dose groups. There was a positive dose-response relationship between log-dose and diarrhea (P=0.01). However, when controlling for other factors, such as onset and cessation of fecal oocyst shedding, dose was not a significant predictor of diarrhea (P=0.5). Onset and cessation of fecal oocyst shedding were found to be the best predictors of diarrhea (P=0.0006 and P=0.04, respectively). The ID₅₀ for fecal oocyst shedding was 5.8 oocysts, for diarrhea was 9.7 oocysts, and for fecal oocyst shedding with diarrhea was 16.6 oocysts. Given that the ID₅₀ of C. parvum is far less than would be excreted into the environment by a naturally infected calf, prevention and control of cryptosporidiosis is a formidable challenge.
authors.affiliation: Department of Animal Science, College of Animal Science, Cornell University, Ithaca, NY 14853, USA. jaz44@cornell.edu
authors.forename: J A
authors.initials: JA
authors.lastname: Zambriski
authors.forename: D V
authors.initials: DV
authors.lastname: Nydam
authors.forename: Z J
authors.initials: ZJ
authors.lastname: Wilcox
authors.forename: D D
authors.initials: DD
authors.lastname: Bowman
authors.forename: H O
authors.initials: HO
authors.lastname: Mohammed
authors.forename: J L
authors.initials: JL
authors.lastname: Liotta
mesh_terms: D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000469:parasitology*; D003457:Cryptosporidiosis / Q000469:parasitology / Q000473:pathology / Q000662:veterinary*; D016785:Cryptosporidium parvum / Q000302:isolation & purification*; D003967:Diarrhea / Q000469:parasitology / Q000662:veterinary; D005243:Feces / Q000469:parasitology; D033661:Oocysts
keywords: Bovine; Calf; Cryptosporidium; Dose–response; Infectious dose