Call for more research
on liver fluke resistance fluke
MORE research is needed to assess the risk from liver fluke resistance to drugs used to control the parasite, according to researchers.
But resistance problems remain low, says the manufacturer of one of the most widely used treatments.
In a Vet Record report, Bristol University researcher Gerald Coles expresses concern about triclabendazole resistance. "To enable vets to advise on therapy of fluke infections, it is important to know which drugs will kill triclabendazole-resistant fluke," he says.
Dr Coless research shows that several drugs are active against adult triclabendazole-resistant fluke. But triclabendazole, present in Combinex and Fasinex, which are made by Novartis, is the only drug active against early immature fluke, says the companys Lynda Maris.
"From August to October, fluke are present at the early immature stage, so treating with drenches which are only effective against adult fluke during this period is a waste of time," she says.
Mrs Maris believes resistance to triclabendazole is, in any event, low. "We encourage any producer to report cases where the drug has not been effective. Since 1998, there have been only five confirmed and one suspected case of resistance.
"The last two wet years have been bad fluke years, so if there was going to be an explosion in resistance cases, we would have expected to see it."
But Dr Coles is concerned over the lack of research. Unlike anthelmintics, where a policy of rotating wormer families is recommended by vets, there is insufficient research evidence to recommend such a policy for flukicides, he says.
"We have no idea how widespread fluke resistance is, as no one is monitoring it.
"Other fluke drugs, including clorsulon and nitroxynil only kill adult fluke, but where there is heavy infection, treatment of immature fluke is needed, leaving triclabendazole." *