Differences in the second internal transcribed spacer (ITS-2) of eight species of gastrointestinal nematodes of ruminants

Genetic differences in the nucleotide sequence of the second internal trans cribed spacers (ITS-2) among Trichostrongylus axei, Trichostrongylus colubr iformis, Ostertagia ostertagi, Cooper ia oncophora, Cooperia punctata, Nema todirus helvetianus, Nematodirus filicollis, and Haemonchus contortus are d escribed. The ITS-2 sequences of the 8 species ranged between 230 and 241 b ase pairs in length. Sequence similarities between the different genera var ied between 60% and 80%. Identities between the different species within a genus varied between 99% for C. oncophora and C. punctata, 95% for T. axei and T. colubriformis, and 89% for N. helvetianus and N. filicollis. The ITS -2 sequences proved to be useful for species differentiation. Except for th e species of Cooperia (2.07% intraspecific variations for C. oncophora and 0.83% for C. punctata) the degree of intraspecific variations (N. filicolli s 0.85%, T. colubriformis 1.26%, T. axel 1.27%, H. contortus 2.60%, O. oste rtagi, and N. helvetianus no variation) was markedly lower than the intersp ecific variations allowing a reliable differentiation within the ITS-2 regi on between single species.