Emerging Infectious Diseases (Dec 1997)

Genetic Polymorphism Among Cryptosporidium parvum Isolates: Evidence of Two Distinct Human Transmission Cycles

  • Michael M. Peng,
  • Lihua Xiao,
  • Amanda R. Freeman,
  • Michael J. Arrowood,
  • Ananias A. Escalante,
  • André C. Weltman,
  • Corinne S.L. Ong,
  • William R. Mac Kenzie,
  • Altaf A. Lal,
  • Charles B. Beard

DOI
https://doi.org/10.3201/eid0304.970423
Journal volume & issue
Vol. 3, no. 4
pp. 567 – 573

Abstract

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We report the results of molecular analysis of 39 isolates of Cryptosporidium parvum from human and bovine sources in nine human outbreaks and from bovine sources from a wide geographic distribution. All 39 isolates could be divided into either of two genotypes, on the basis of genetic polymorphism observed at the thrombospondin-related adhesion protein (TRAP-C2) locus. Genotype 1 was observed only in isolates from humans. Genotype 2, however, was seen in calf isolates and in isolates from a subset of human patients who reported direct exposure to infected cattle or consumed items thought to be contaminated with cattle feces. Furthermore, experimental infection studies showed that genotype 2 isolates were infective to mice or calves under routine laboratory conditions, whereas genotype 1 isolates were not. These results support the occurrence of two distinct transmission cycles of C. parvum in humans.

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