Author
 |
Fayer, Ronald |
|
Submitted to: International Giardia and Cryptosporidium Conference
Publication Type: Abstract Only Publication Acceptance Date: 3/26/2007 Publication Date: 5/13/2007 Citation: Fayer, R. 2007. Advances in Cryptosporidium Research. International Giardia and Cryptosporidium Conference, May 13-18, 2007, Moreilia-Michoacan, Mexico. (Spiral Bound Book). Interpretive Summary: Technical Abstract: The genus Cryptosporidium is one of over 300 genera that include 4800 named species in the phylum Apicomplexa. There are 16 species of Cryptosporidium and nearly 40 unnamed cryptosporidia called genotypes based on significant rRNA or other gene sequence differences. A genotype is a temporary descriptor, not a taxon. Most studies on the biology, morphology, biochemistry, host preferences, immunology, pathogenicity, physiology, and prevalence have been conducted on C. parvum, a species of medical and veterinary importance, because it is geographically widespread, infects many host species, produces many oocysts making it easily obtainable, and can be grown and tested in vitro and in vivo. Data from C. parvum have become generalized and extended to others in the genus. Gene sequence information, based primarily on the SSUrRNA gene, has become essential for defining new species including C. andersoni, C. bovis, C. canis, C. galli, C. hominis, and C. suis. The Cryptosporidium genome, smaller than those of most other apicomplexans, consists of ~9.1-megabases in 8 chromosomes with possibly over 3,800 genes. It lacks mitochondrial genes, genes for a Krebs cycle, and those for most de novo synthesis including fatty acids, amino acids and nucleosides, indicating that a host is essential for providing its nutrients. Consequently, reports of new extracellular life-cycle stages in cell cultures and in cell-free media, have stimulated controversy. C. parvum and C. hominis genomes differ in most important metabolic pathways from other apicomplexa, explaining why drugs targeted for Plasmodium, Toxoplasma and Eimeria fail to treat cryptosporidiosis. These genomic data provide new targets for proteins unique to Cryptosporidium, some found in bacteria and plants.Research on the functions and biological roles of genes and gene products has begun. Electron microscopy and biochemical studies have elucidated mechanisms of host cell invasion and internalization of sporozoites. Newly identified proteins include: surface proteins (glycoproteins and lipoproteins) potentially involved in parasite-host cell interactions and immune evasion, P-type ATPases involved in cation transport, and thrombospondin-related adhesive proteins. Identification of 9 oocyst wall proteins and the finding of molecules containing N-acetyl-galactosamine on the surface of oocysts, indicate the complex chemical structure of oocyst walls. Environmental studies have shown that vegetative buffer strips, wetlands, ponds, and invertebrate predators can reduce oocyst numbers that reach watersheds. Detection methods have been modified and improved. The rate of acquisition of new information on this genus has been phenomenal. The foregoing and much more have taken place in less than a decade. |
