Victorian winter rainfall
Liver fluke control
Liver fluke (Fasciola hepatica) only occurs where the intermediate host (lymnaeid snails) are present. These snails are found where there are slow-moving creeks, swamps or springs and they can survive in mud when water flow temporarily stops. However, the snail is not necessarily present in all such areas.
Liver fluke may not be present on all paddocks or properties in a ‘flukey’ locality.
Roundworms are often specific to one type of animal, but liver fluke can infect many species including cattle, sheep, goats, alpacas and horses, as well as humans and wild animals.
Grazing management can help prevent liver fluke infection. Unfortunately, there is currently no effective method to breed for host resistance to liver fluke.
If liver fluke is present on a property, infection can be prevented or minimised by:
Testing for liver fluke can be done using the dung samples sent for a WormTest. A fluke test, which uses a different method to that used for roundworms, must be specifically requested.
If you don’t know whether your sheep are infected with liver fluke, test twice a year (late summer and winter) for at least two years (i.e. 4 tests).
Testing will show whether liver fluke is present and to what extent.
You can also determine which paddocks are affected by testing mobs that have only been run in a particular paddock since the last fluke-treatment.
If fluke egg counts for a particular paddock are frequently high (greater than 25–50 eggs per gram), there may be significant production losses. Reconsider your grazing strategies for the affected paddocks and see if fluke-affected areas can be fenced off.
If results at the testing times are not always positive, then continue testing at the specified times to decide whether to drench.
If all tests have been negative and the livers of dead or slaughter sheep have not shown any signs of liver fluke, it is likely that the host snails are not present on your property to transmit liver fluke.
Drenching for fluke will not be required (except to remove fluke from sheep brought onto the property).
A blood test (antibody [ELISA] test) is also available from various laboratories, for example, the NSW Department of Primary Industries State Veterinary Laboratory at Menangle.
Any positive fluke egg count is significant and indicates treatment is needed.
If testing for two years confirms that sheep are infected at all test times, then ongoing testing can be stopped. In this case, routine treatments for liver fluke should be given to sheep that have been grazing the affected paddocks in:
An important alternate strategy, where only a small portion of the farm is affected, is treatment either onto (before grazing) or off (after grazing) the affected paddock(s), or both.
Some treatments for roundworms (scour worms and barber’s pole worm) will control various stages of liver fluke. Check the label as some are only effective against mature fluke (see Table 1).
The most important treatment is carried out in winter and should be based on the flukicide, triclabendazole, which is effective against all stages of the fluke found in the sheep. If treatments are also required in February–March, this treatment should be a flukicide other than triclabendazole (if this was used in winter). This treatment rotation will reduce the rate of development of fluke resistant to triclabendazole.
When bringing in sheep from another property, consider including a fluke treatment in the quarantine drench if their fluke status is unknown. Bear in mind that adult liver fluke can live for several years inside host animals.
Table 1. Fluke treatments and stage of fluke against which they are effective.
|Active||Age of fluke killed|
|Albendazole||From 12 weeks|
|Closantel||From 8 weeks|
|Closantel plus oxfendazole*||From 6 weeks|
|Closantel plus albendazole*||From 8 weeks|
|Oxyclozanide plus levamisole||From 12 weeks|
Source: from Liver fluke disease in sheep and cattle, by J Boray (March 2007) NSW DPI Primefact 446
*No commercial products with this combination are currently available.
The following drench actives do not control liver fluke:
Resistance has developed to various flukicides. Rotate between flukicides from different chemical groups, beginning with triclabendazole for the winter treatment.
More detailed information on liver fluke can be found at the NSW DPI web site by clicking here.