PCR-based identification of individuals of Schistosoma japonicum representing different subpopulations using a genetic marker in mitochondrial DNA

A mitochondrial NADH dehydrogenase I gene fragment (NDI) was sequenced for three laboratory maintained isolates of Schistosoma japonicum. Comparison o f sequences representing the isolates (originally obtained from the Anhui a nd Zhejiang provinces of the People's Republic of China, and from the Phili ppines) revealed inter-isolate sequence variations of 0.2-0.6% and no intra -isolate variation was round. the sequences also indicated that while the a mplification products of the Zhejiang and Philippine isolates contained a r ecognition site for the endonuclease RsaI, there was no such site in the An hui isolate. This was tested by digesting amplification products from a num ber of individual worms with RsaI. Then an infection experiment was designe d to test the value of this genetic marker for studies of the population bi ology of S. japonicum in the final host. For this, the two Chinese isolates were used. Three groups of mice (A-C) were exposed firstly to a primary in fection and then challenge-infected at weeks 4 and 7 of the experiment. In group A the first infection was done with the Anhui isolate, and the two ot hers with the Zhejiang isolate, thereby providing a specific, detectable co hort. In groups B and C the Anhui isolate was used for the second and third infection. All mice were perfused 5 weeks after the last challenge infecti on, and the NDI was subsequently amplified from DNA of the perfused worms a nd digested with RsaI. The digestion revealed that while infection groups A and B contained mixed populations of the Anhui and Zhejiang isolates, only Zhejiang worms were present in group C. We concluded that the absence/pres ence of the RsaI site in the NDI provides a useful marker for the delineati on of cohorts of S. japonicum. (C) 1999 Australian Society for Parasitology Inc. Published by Elsevier Science Ltd. All rights reserved.