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WormBoss worm control program

Tasmania

 

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.

Prevention

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:

  • isolating the areas that harbour the snail, using fencing
  • conducting earthworks to deepen shallow water, or to improve drainage
  • repairing broken pipes and troughs that have resulted in permanent wet areas
  • avoiding grazing of snail-infested areas by the most susceptible animals (sheep, goats, alpacas and young cattle)

Detection

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 three times a year (autumn, winter and summer) for at least two years (i.e. 6 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 three testing times are not always positive, then continue testing at the specified times to decide whether to drench.

If all six 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 lymnaeid snails are not present on your property to act as a host for 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. Also, a faecal antigen test for fluke is available through Charles Sturt University’s Veterinary Diagnostic Laboratory

Response

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:

  • at the first summer drench (late January/early February)
  • 1 or 2 more drenches may be required in early April and in May
  • August/September

In areas with fluke only in wet years (such as in lower reaches of valleys), give 2 drenches:

  • late autumn
  • late winter

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 worms) 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 April–May 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 August–September and/or February, one or both of these treatments should be a flukicide other than triclabendazole (if this was used in April). 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 the age of fluke from which they are effective

Active Age of fluke killed
Triclabendazole All stages
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:

  • moxidectin, abamectin or ivermectin
  • oxfendazole and fenbendazole
  • levamisole
  • naphthalophos and pyraclofos
  • monepantel
  • derquantel
  • praziquantel

Resistance to flukicides

Resistance has developed to various flukicides. Rotate between flukicides from different chemical groups, beginning with triclabendazole for the April–May treatment.

More detailed information on liver fluke can be found at the NSW DPI web site:
http://www.dpi.nsw.gov.au/agriculture/livestock/sheep/health