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Submitted to: Food Safety Consortium Proceedings
Publication Type: Abstract Only Publication Acceptance Date: 5/1/2005 Publication Date: 5/24/2005 Citation: Santin, M. 2005. Overview of the Epidemiology of Cryptosporidium and Giardia. 13th Annual Food Safety Farm to Table Conference, Mary 24-25, 2005, Moscow, Idaho. Interpretive Summary: Technical Abstract: Giardia and Cryptosporidium are enteric protozoan parasites that infect a wide range of vertebrate hosts. Both are well known agents of diarrheal disease in animals and humans worldwide. Cryptosporidium and Giardia are transmitted by direct fecal/oral contact or by ingestion of food or water contaminated with the oocyst stage of Cryptosporidium or the cyst stage of Giardia. For Cryptosporidium, in human clinical specimens the two most commonly detected Cryptosporidium are Cryptosporidium parvum and Cryptosporidium hominis. C. hominis was previously known as genotype 1 and C. parvum as genotype 2 or bovine genotype. Molecular studies have demonstrated C. hominis primarily in humans and have shown it to be a clonal population. In contrast, C. parvum was shown to consist of multiple populations, one associated only with humans, another associated with both humans and cattle, and others associated with other host species. This means that at two or more transmission cycles have been demonstrated, the anthroponotic cycle for human to human transmission of C. hominis and the zoonotic cycle for animal-human transmission of C. parvum, and animal-animal transmission. However these two species are not the only ones affecting humans. Infections by other species and genotypes of Cryptosporidium (including C. meleagridis, C. canis, C. felis, C. muris, C. suis and cervine genotype), have also been reported in immuno-competent and in immuno-compromised patients. For Giardia, the similar morphology within G. intestinalis masks genetic and biotypic differences that are large enough for G. intestinalis now to be considered a species complex. Giardia infectious for humans falls exclusively into Assemblages A and B. Some animal-derived isolates appear to be similar or identical to human-derived genotypes while others represent unique genotypes that seem to be host specific. Water is recognized as an important vehicle of transmission for both parasites. Outbreaks have been linked recreational and drinking water as well as to the consumption of contaminated food. The complex epidemiology of cryptosporidiosis and giardiasis is complicated by the use of morphologic criteria to identify species/genotypes of human vs. non-human pathogens. However, the implementation of molecular tools is helping to clarify Cryptosporidium and Giardia diversity and improve our understanding of these parasites. Valid identification is essential to determine sources of infection in outbreaks and risk factors associated with the transmission. |
