Efficacy of fasciolicides available for use in sheep
in the UK against susceptible fluke populations
(adapted from
Fairweather and Boray, 1999).
TCB is
the most widely used fasciolicide because of its activity against immature
fluke. Unfortunately this has led to the development of resistance in several
countries and reports of suspected resistance in the UK. Resistance usually
manifests first as a failure to kill the youngest immatures, with subsequent
re-appearance of fluke eggs in the faeces earlier than would be expected if
the drug retained full efficacy. As resistance develops eventually adult
fluke are able to survive treatment as well. The possibility of other reasons
for fasciolicide failure should always be considered, particularly if animals
are in poor condition or may be suffering from liver damage. Where resistance
is suspected to a particular product, then an alternative fasciolocide should
be considered, taking into account the variations in activity against
immature fluke between products.
See Section 7.5.1
of the text, Sustainable Worm Control in Sheep.
