Identification of Dictyocaulus spp. in ruminants by morphological and molecular analyses

Lungworms of the genus Dictyocaulus from cattle, roe deer, and moose in Sweden were subjected to morphological and molecular analyses. The objectives of the study were to investigate whether mixed or monospecific Dictyocaulus infections occur in Swedish cattle and whether wild cervids may act as reservoirs. The morphological characters examined were thickness and shape of the buccal capsule wall (BCW) and total spicular length (TSL). Morphometry was also done on the total body length, and BCW thickness and length. In the molecular identification, we used a PCR-linked hybridization assay to probe worm DNA with species-specific oligonucleotide probes to the second internal transcribed spacer (1TS2). The results showed that the BCW shape was the most reliable morphological character for identification. Significant differences were observed in this character, but an overlap occurred between lungworms from each of the host species. With the hybridization assay, all lungworms from cattle were identified as D. viviparus, whereas those from roe deer represented a novel Dictyocaulus species demonstrating that each host had a monospecific lungworm infection. In moose, 61 (78.2%) worms belonged to the new species and 17 (21.8%) were D. eckerti. This study shows the usefulness of hybridization assay as an epidemiological tool for the specific identification of lungworms of cattle and wild cervids.