Characterisation of Ascaris from human and pig hosts by nuclear ribosomal DNA sequences

The sequences of the nuclear ribosomal DNA region spanning the first intern al transcribed spacer, the 5.8S rRNA gene and the second internal transcrib ed spacer were determined for Ascaris samples from pigs and humans from dif ferent geographical regions. The sequences of the 5.8S gene and the second internal transcribed spacer were the same for all samples examined, whereas all Ascaris samples from humans had six (1.3%) nucleotide differences in t he first internal transcribed spacer compared with those from pigs. These d ifferences provided some support for the existence of separate species of A scaris or population variation within this genus. Using a nucleotide differ ence within a site for the restriction enzyme HaeIII, a PCR-linked restrict ion fragment length polymorphism method was established which allowed the d elineation of the Ascaris samples from pigs and humans used herein. Exploit ing the sequence differences in the first internal transcribed spacer, a PC R-based single-strand conformation polymorphism method was established for future analysis of the genetic structure of pig and human Ascaris populatio ns in sympatric and allopatric zones. (C) 1999 Australian Society for Paras itology. Published by Elsevier Science Ltd. All rights reserved.