Epidemiology of fascioliasis in Denmark. Studies on the seasonal availability of metacercariae and the parasite stages overwintering on pasture

• Published in: Veterinary parasitology Vol. 5; no. 2; pp. 145 - 154
• Main Authors: Shaka, Stephen, Nansen, Peter
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.01.1979
• Subjects: sheep; Denmark
• ISSN: 0304-4017; 1873-2550
• DOI: 10.1016/0304-4017(79)90006-2

A 3-year experiment was designed to study (by means of tracer lambs) the seasonal fluctuation in the availability of infective metacercariae. Particular attention was paid to the role played by infection overwintering in the field. The results showed that (1) there was a marked onset of metacercarial availability in July or August and relatively high numbers of parasites were acquired during the rest of the grazing season; (2) the majority of parasites ingested from midsummer onwards originated from ‘summer infection’ of snails; (3) the availability of larvae originating from over-wintered field infection followed a characteristic pattern. In spring and early summer no or few metacercariae were acquired, whereas in July or August the number of ingested larvae increased markedly, constituting a minor, though not negligible, proportion of the late summer infection. The late onset of availability of metacercariae from an overwintered source of field infection overlapped the availability of metacercariae originating from eggs deposited in the field during the same season. This finding is compatible with the assumption that one important means of overwintering in the field is in the form of eggs.