Evidence for the existence of a sheep and a goat line of Teladorsagia circumcincta (Nematoda).

Populations of Teladorsagia circumcincta harbored by sheep and goats were investigated by means of isoenzyme electrophoresis. Genetic characterization of 16 natural goat populations was based on 5 polymorphic enzymes. Malate dehydrogenase (MDH-1) was the most informative; it had three alleles, the electrophoretically fast migrating one being named sR. We distinguished three groups with presence to over 20%, low frequency, and absence of sR, respectively. In four sheep flocks, only the third group was found. Neither of two laboratory-reared lamb populations originating from two geographic origins presented this third allele. When populations of worms with high sR frequency were passaged into lambs, a steep decrease in the sR-allele frequency was recorded, which was no longer demonstrated in lambs after the third passage. We suggest that the worms lacking the third allele belong to the sheep line and that those with the sR allele belong to the goat line. Thus, goats would be infected with worms of both goat and sheep lines, whereas sheep would harbor only the sheep line.