Differences in the second internal transcribed spacer (ribosomal DNA) between five species of Trichostrongylus (Nematoda: Trichostrongylidae).

The second internal transcribed spacer (ITS-2) of the ribosomal DNA of 5 species of Trichostrongylus has been sequenced. The ITS-2 of the 5 species was 237 or 238 bases in length, and had a GC content of approximately 30%. No evidence of intraspecific variation was detected in the ITS-2 sequence of T. colubriformis, T. vitrinus or T. retortaeformis, irrespective of the life cycle stage examined. There was evidence, however, of variation at five positions in the ITS-2 sequence of T. vitrinus samples and at one position in T. axei, indicating intra-individual variation in the sequence of different copies of the ribosomal DNA. Nonetheless, there were consistent sequence differences between the five Trichostrongylus species examined. The level of interspecific differences in nucleotide sequence was low (1.3-7.6%), with the species infecting birds (T. tenuis) being genetically more different to the four species found in mammals. Some of the nucleotide differences between species occurred at the recognition sites of endonucleases, which makes them of important diagnostic value for species identification. Also of significance are the recognition sites for several enzymes located within the regions of sequence homology for the five species of Trichostrongylus. These may prove useful in distinguishing between genera of trichostrongyle nematodes.