Submitted to: International Journal for Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 13, 1999
Publication Date: December 1, 1999
Interpretive Summary: Parasites of the genus Cryptosporidium cause diarrheal disease in a wide range of vertebrates. The genus Cryptosporidium contains eight named species based on a combination of physical characteristics of the oocyst stage (the stage found outside the body) and the range of hosts susceptible to infection with oocysts of that species. The small size of oocysts that appear identical and the fact that some animal species can become infected with genetically different isolates of Cryptosporidium makes species identification within this genus very difficult. Molecular techniques and gene loci are described herein that aid in the identification and differentiation of species of Cryptosporidium. These molecular characteristics support some of the named species as valid. Under the umbrella of other named species there appear to be several physically identical unnamed species that are genetically and biologically different. Based on these findings, it is proposed that the systematics of this genus be re-examined. Recogniton of new species will aid in the identification of clinical and environmental specimens, helping to resolve questions as to the sources of infection and aiding in prevention strategies.
Isolates of Cryptosporidium were genetically characterized using nucleotide sequence analysis of the 18S rRNA and dihydrate folate reductase genes and also RAPD analysis. Phylogenetic analysis confirmed the validity of existing species of Cryptosporidium such as C. muris and C. baileyi and also confirmed the mounting evidence from numerous researchers worldwide that C. parvum is not a single uniform species. The data obtained provided strong support for the validity of C. felis and there was also evidence to suggest that the newly identified marsupial and pig genotypes may also be distinct and valid species.