Abstract
The guanaco (Lama guanicoe) is the major inhabitant and the largest wild artiodactyl in Patagonia. The introduction of invasive species into its ecological niche poses ecological risks, since invasive species may introduce harmful parasites to this native species. In this work, filariform larvae of the Nematodirus genus were found in feces of guanacos from the Perito Moreno National Park in Argentina. All species were characterized according to morphological features and molecular analyses using ribosomal DNA (rDNA). For the molecular analysis, rDNA fragments were amplified by PCR and then sequenced. The results of the BLASTN comparison threw a 99 % of identity with Nematodirus spathiger and 97 % with N. helvetianus, suggesting that N. spathiger is the infecting parasite. Nematodirus spathiger together with N. filicollis and N. battus causes diarrhea and deaths in sheep and, in some cases, in South American camelids. The availability of more accurate diagnostic methods such as PCR could improve the control measures for gastrointestinal helminthiasis.