Submitted to: Memorias Do Instituto Oswaldo Cruz
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 9, 1998
Publication Date: N/A
Interpretive Summary: Cryptospordium parvum causes waterborne and foodborne disease in humans. Lack of genetic information on this and other related species that do not infect humans has resulted in confusion in diagnosis and in epidemiologic studies intended to determine the sources of infection. The gene for small subunit ribosomal RNA was studied for 4 species of Cryptosporidium and for isolates within these species. Information from this study has been applied as a diagnostic tool for clinical and environmental specimens. Data have shown that most human infections result from C. parvum genotype 1 (transmissible from human to human) whereas most environmental contamination is due to C. parvum genotype 2 (transmissible from animals to humans).
Cryptosporidiosis has recently attracted attention as an emerging waterborne and foodborne disease and an opportunistic infection in HIV infected individuals. The lack of genetic information, however, has resulted in confusions in the taxonomy of Cryptosporidium parasites and in the development of molecular tools for the identification and typing of oocysts in environmental samples. Phylogenetic analysis of the small subunit ribosomal RNA (SSU rRNA) gene has shown that the genus Cryptosporidium is comprised of several distinct species. Our data show the presence of at least four species: C. parvum. C. muris, C. baileyi and C. serpentis (C. meleagridis, C. nasorum and C. felis were not studied). Within each species, there is some sequence variation. Thus, various genotypes (genotype 1, genotype 2, guinea pig genotype, monkey genotype and koala genotype, etc.) of C. parvum differ from each other in six regions of the SSU rRNA gene. The information on the polymorphism in Cryptosporidium parasites has been used in the development of species and strain-specific diagnostic tools. Use of these tools in the characterization of oocysts from clinical and oyster samples indicates that C. parvum genotype 1 is the strain responsible for most human Cryptosporidium infections, whereas genotype 2 is probably the major source for contamination of environment. No non-C. parvum parasites are detected in HIV+ individuals, indicating that the disease in humans is caused only by C. parvum.