PC Sheep Liver Fluke2020 FINAL

PAGE 6

Understanding Liver Fluke in Sheep Flocks

Weeks post-infection

1 2 3 4 5 6 7 8 9 10 11 12+

Triclabendazole (TCBZ)

-

90-99%

>99%

Rafoxanide Closantel, Nitroxynil

-

50-90%

91-99%

-

50-90%

91-99%

Albendazole, Oxyclozanide *

-

50-70% 80-99%

* Albendazole and oxyclozanide are available but have no effect on liver fluke less than 10 weeks old and are not normally recommended. However, they may be suitable for chronic disease or where triclabendazole resistance occurs.

Table 2: Examples of the effectiveness of drugs used to control liver fluke infection

Timing of treatments In order to protect the efficacy of flukicide drugs it is recommended that different active compounds are used in rotation to avoid over-exposure of a liver fluke population to a single drug treatment. A common rotation regime involves using closantel or nitroxynil in the spring and triclabendazole in the autumn/winter. Treatment plans should be tailored to specific farms. Treatment failure and drug resistant parasites Treatment failure and drug resistance are easily confused but are different concepts. Treatment failure occurs when parasites are exposed to a lower than recommended dose of the drug (or when the wrong drug is used relative to the stage of infection). Drug resistance is present when parasites survive in the presence of a drug at a dose that would usually kill them. Failing to administer drug treatments correctly, or at the right dose, increases the risk of drug resistance in a parasite population. Some tips for successful treatment: • Choose an active compound appropriate to the stage of infection. • Check that scales are accurate to weigh animals (or at least the largest animal in each group of the same age/ condition) and dose according to weight. • Calibrate the dosing gun regularly, and before each period of dosing. • Dose carefully using the correct technique. • Store drugs correctly and only use previously opened products in accordance with manufacturers’ recommendations. • Rotate the drugs used on-farm to avoid developing resistance. • Ensure treatment against early immature fluke is as early as possible based on previous farm experience. Treating animals that are already ill, or where mortality has occurred, can result in diminished treatment success in the remainder of the group. Resistance to anthelmintic drugs, including triclabendazole, has already been reported in many countries, including Ireland. After ruling out inadequate dosing or the incorrect product for the infection stage, if resistance is suspected on farm, faecal egg count reduction testing can help establish treatment efficacy (see Technical box).

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