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Genetic polymorphism among Cryptosporidium parvum isolates: evidence of two distinct human transmission cycles
M M Peng1, L Xiao, A R Freeman
1University of Michigan, Ann Arbor, USA.
Abstract:
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 faces. 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.
Insights
Molecular analysis revealed two distinct genotypes of Cryptosporidium parvum. Genotype 1 infects humans only, while genotype 2 infects animals and humans, suggesting separate transmission cycles.
Area of Science:
- Microbiology
- Genetics
- Epidemiology
Background:
- Cryptosporidium parvum is a significant cause of diarrheal disease in humans and animals.
- Understanding C. parvum transmission dynamics is crucial for public health interventions.
Purpose of the Study:
- To investigate the genetic diversity of Cryptosporidium parvum isolates.
- To determine the distinct transmission cycles of C. parvum in humans and animals.
Main Methods:
- Molecular analysis of 39 C. parvum isolates from human and bovine sources.
- Genotyping based on genetic polymorphism at the thrombospondin-related adhesion protein (TRAP-C2) locus.
- Experimental infection studies in mice and calves.
Main Results:
- Two distinct genotypes (Genotype 1 and Genotype 2) were identified among the isolates.
- Genotype 1 was exclusively found in human isolates.
- Genotype 2 was found in calf isolates and in humans with direct cattle exposure, and was infective to mice and calves.
Conclusions:
- The findings support the existence of two separate transmission cycles for C. parvum.
- Genotype 1 appears to be human-specific, while Genotype 2 involves zoonotic transmission.
- This genetic differentiation has implications for controlling C. parvum outbreaks.