Polymorphisms in the beta-tubulin gene of Cryptosporidium parvum differentiate between isolates based on animal host but not geographic origin

Polymerase chain reaction primers were designed to target a region of the C ryptosporidium parvum beta-tubulin gene spanning an intron. Amplification p roducts contained II polymorphic positions, representing a sequence diverge nce of 1.8%, which discriminated between isolates of C. parvum found solely in humans (genotype 1) and those found in humans and animals (genotype 2). Seven of the polymorphic sites were located outside of the intron and the polymorphism between isolates was readily demonstrated by HaeIII restrictio n digestion. However, all of the sequences from genotype 1 human-derived oo cysts isolated in the United States and Australia were conserved. Also, the re were no sequence differences between bovine isolates obtained from both continents. Therefore, isolates could not be differentiated based on geogra phic source of origin.