Sequencing of the beta-tubulin genes in the ascarid nematodes Parascaris equorum and Ascaridia galli

Benzimidazoles (BZ) are used to control infections of the equine roundworm Parascaris equorum and the poultry roundworm Ascaridia gall. There are still no reports of anthelmintic resistance (AR) to BZ in these two nematodes, although AR to BZ is widespread in several other veterinary parasites. Several single nucleotide polymorphisms (SNP) in the beta-tubulin genes have been associated with BZ-resistance. In the present study we have sequenced beta-tubulin genes: isotype 1 and isotype 2 of P. equorum and isotype 1 of A. galli. Phylogenetic analysis of all currently known isotypes showed that the Nematoda has more diversity among the beta-tubulin genes than the Vertebrata. In addition, this diversity is arranged in a more complex pattern of isotypes. Phylogenetically, the A. galli sequence and one of the P. equorum sequences clustered with the known Ascaridoidea isotype 1 sequences, while the other P. equorum sequence did not cluster with any other beta-tubulin sequences. We therefore conclude that this is a previously unreported isotype 2. The beta-tubulin gene sequences were used to develop a PCR for genotyping SNP in codons 167, 198 and 200. No SNP was observed despite sequencing 95 and 100 individual adult worms of P. equorum and A. galli, respectively. Given the diversity of isotype patterns among nematodes, it is likely that associations of genetic data with BZ-resistance cannot be generalised from one taxonomic group to another. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved.