By Bruce Watt, Regional Veterinarian, Central Tablelands Local Land Services

October 2015

Technical assistance for this article was also provided by Stephen Love (DPI NSW) and Rob Woodgate (CSU).

Liver fluke infestations (fascioliasis) are common in sheep, cattle and goats in the NSW Central Tablelands. We know from on-farm surveys and abattoir surveillance that at least 80% of Central Tablelands properties have fluke, especially those to the east. Despite this high prevalence, we rarely see clinical liver fluke disease such as that illustrated in the photographs below.

It seems that current fluke programs are reasonably effective at controlling clinical disease, which can range from ill thrift, bottle jaw, anaemia and jaundice through to sudden deaths. Generally, stock are treated in the important April–May (or sometimes later in the winter) window with triclabendazole-based drenches. Less often, stock are treated again in August–September and sometimes in December as well.

Figure 1. Sheep with severe fluke infestation including damaged liver which has adhered to the diaphragm.

However, some questions arise. Despite the rarity of clinical fluke disease, tablelands producers could be sustaining subclinical (undetected) production losses. This is not always easy to determine, but given that abattoirs report a high proportion of livers from sheep originating from the tablelands have evidence of fluke infestation, it is likely that sub-clinical losses are occurring.

So, these are the relevant questions:

• Do you have liver fluke?
• If so, is your current program effective?
• Are the flukicides you use, including triclabendazole, effective?

Testing for liver fluke

Clearly, livestock producers in the Central Tablelands and other ‘flukey’ areas—need to monitor for fluke. Most of your neighbours probably have liver fluke; do you?

How do you test for liver fluke?

There are three tests available:

• The liver fluke egg count. This requires faecal samples and is the most commonly used test. This test is different from the egg count for roundworms, so you need to specifically request a liver fluke egg count. Be aware that it takes 8–10 weeks from the time of infection for fluke eggs to appear in the faeces. In the meantime there could be significant liver damage and blood loss if infections are heavy.
• The liver fluke antibody ELISA. This is available from various laboratories, for example, the NSW Department of Primary Industries State Veterinary Laboratory at Menangle. It measures antibodies in the blood, which animals produce in response to fluke infections. Blood tests of particular mobs will pick up exposure to fluke over the previous three months even if eggs are not present in the manure. However it takes 6–8 weeks after infection for the test to go positive and, after fluke are removed by a flukicide, it takes another 6–8 weeks or so for antibody levels to go down.
• The fluke faecal antigen test. This is a newer test, and is offered by the Veterinary Diagnostic Laboratory at CSU at Wagga Wagga. It detects parts (antigens) of the fluke shed in the faeces. It may be a useful option to determine the fluke status of your mob or property. Australian research on the best use of this test is nearing completion. The findings will be reported soon in a WormBoss article.
• Post-mortem examination of livers of a number of animals for damage, including scarring, and thickened bile ducts, which may also contain adult flukes.

Consult with your adviser, but you will probably start monitoring by using fluke egg counts. Begin by requesting a fluke as well as a roundworm egg count when you next send samples to the lab.

When are good times to test?

April-May, August (remember the months starting with A) and summer are good times to test the mob, in addition to testing animals you think could have fluke disease (i.e. sheep with anaemia or jaundice or not doing as well as expected). To determine whether fluke occurs on your property, do not rely on a single test, but do repeated testing over a number of seasons. Numbers of fluke can vary enormously from paddock to paddock and season to season.

Check your fluke drenches

Monitoring can also be used to test whether the most recently used treatment has been effective. With nematodes (e.g. scour worms and barber’s pole worm) do a worm egg count before and 10–14 days after drenching to test the effectiveness of an anthelmintic.

With liver fluke, test before and 21–28 days after treatment. Fluke egg counts may not be high enough to give a precise estimate of flukicide efficacy, but  they are still worth doing. If your flukicide is effective, the fluke egg count will normally go down by at least 90% by 21–28 days post-treatment. 

As to the antibody ELISA test, remember that antibodies may be detected for three months even if all the fluke have been killed.

The fluke faecal antigen test can have an important role here, with overseas research suggesting faecal samples collected 21–28 days after a fully effective treatment should test negative for antigen.  Final recommendations on when to use this test under Australian conditions will be published later this year.

Rotate between unrelated flukicides

Triclabendazole resistance has been reported in parts of NSW, although our recent and limited testing has not found it on the Central Tablelands.

Producers should rotate between unrelated flukicides, reserving the most effective drenches (triclabendazole-based drenches, and Nitromec^®(cattle)) for the April–May treatment. In addition to triclabendazole-based drenches, the other options are (a) various products with closantel (not for cattle), (b) a combination of levamisole and oxyclozanide (Nilzan^®), and (c) various products with albendazole (which aids in the control of adults, but does not kill immatures). In cattle, as mentioned, there is also the nitroxynil/clorsulon/ivermectin combination (Nitromec^®).

The WormBoss Drenches section allows you to search for products, including those effective against liver fluke.