GENETIC-POLYMORPHISM AMONG CRYPTOSPORIDIUM-PARVUM ISOLATES - EVIDENCEOF 2 DISTINCT HUMAN TRANSMISSION CYCLES

We report the results of molecular analysis of 39 isolates of Cryptosp oridium parvum from human and bovine sources in nine human outbreaks a nd from bovine sources from a wide geographic distribution. All 39 iso lates could be divided into either of two genotypes, on the basis of g enetic polymorphism observed at the thrombospondin-related adhesion pr otein (TRAP-C2) locus. Genotype 1 was observed only in isolates from h umans. Genotype 2, however, was seen in calf isolates and in isolates from a subset of human patients who reported direct exposure to infect ed cattle or consumed items thought to be contaminated with cattle fec es. Furthermore, experimental infection studies showed that genotype 2 isolates were infective to mice or calves under routine laboratory co nditions, whereas genotype 1 isolates were not. These results support the occurrence of two distinct transmission cycles of C. parvum in hum ans.