Comparison of Internal Transcribed Spacers and Intergenic Spacer Regions of Five Common Iranian Sheep Bursate Nema¬todes

Accurate identification of sheep nematodes is a critical point in epidemiologi­cal studies and monitoring of drug resistance in flocks. However, due to a close morphological similarity between the eggs and larval stages of many of these nema­todes, such identification is not a trivial task. There are a number of studies show­ing that molecular targets in ribosomal DNA (Internal transcribed spacer 1, 2 and Inter­genic spacer) are suitable for accurate identification of sheep bursate nematodes. The objective of present study was to compare the ITS1, ITS2 and IGS regions of Ira­nian common bursate nematodes in order to choose best target for specific identifica­tion methods. The first and second internal transcribed spacers (ITS1and ITS2) and inter­genic spacer (IGS) of the ribosomal DNA (rDNA) of 5 common Iranian bursate nema­todes of sheep were sequenced. The sequences of some non–Iranian isolates were used for comparison in order to evaluate the variation in sequence homology between geographically different nematode populations. Comparison of the ITS1 and ITS2 sequences of Iranian nematodes showed greatest similarity among Teladorsagia circumcincta and Marshallagia marshalli of 94% and 88%, respectively. While Trichostrongylus colubriformis and M. marshalli showed the highest homology (99%) in the IGS sequences. Comparison of the spacer sequences of Iranian with non-Iranian isolates showed significantly higher variation in Haemonchus contortus compared to the other species. Both the ITS1 and ITS2 sequences are convenient targets to have spe­cies-specific identification of Iranian bursate nematodes. On the other hand the IGS region may be a less suitable molecular target.