Molecular characterization of Cryptosporidium parvum isolates obtained from humans

Fifty stool specimens collected from severe diarrheic patients attending Misr University Hospital, were examined microscopically for protozoan parasites mainly, Cryptosporidium parvum. Stool examination revealed 22 cases with C. parvum, 8 with E. histolytica, 14 with G. intestinalis and six were parasite-free. The results were compared with the established nested PCR assay to detect DNA directly from stool specimens. After the extraction of DNA from stool, a 402-bp fragment of C. parvum DNA was amplified with two 26-mer outer primers. The amplified products, 194-bp DNA fragment, were used for a second run. This study indicated that the used primers are specific for DNA of C. parvum. The PCR detected a total of 28 positives; six of these cases were negative by AF stool examination, which eventually confirmed to be positive by several successive examinations of the stool and/or duodenal aspiration. Microscopy exhibited 78.5% sensitivity and 100% specificity compared to 100% specificity and sensitivity with PCR. Consequently, PCR is more sensitive and easier to interpret but required more hands-on time to perform and is more expensive than microscopy. However, PCR batch analysis reduces the cost considerably.