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Testing for liver fluke in sheep

There are a number of diagnostic tests available to use when looking for liver fluke. Unfortunately, none of them on their own will give us all the information we need at all times of year, so we need to use a combination of different tests and information from other sources to fully understand where and when the fluke challenge is likely to happen on any farm.

The table below shows the best times to use each test:

Test for liver fluke Spring Summer Autumn Winter
Fallen stock liver check right-sign right-sign right-sign right-sign right-sign right-sign
Abattoir returns right-sign right-sign right-sign right-sign
Fluke antibody test cross-sign ? right-sign right-sign right-sign
Coproantigen test right-sign ? right-sign right-sign right-sign
Fluke egg detection right-sign ? cross-sign right-sign

Key:

right-sign right-sign

very good time to use this test

right-sign

good time to use this test

?

maybe a good time to use this test

cross-sign

not a good time to use this test

Test Why this test? Which test when and why?
Post mortem examination of fallen stock Never waste a dead sheep! Even if you are certain the animal died for another reason, it is worth checking the condition of the liver to see if there is any damage or liver fluke present. This is especially important in the early autumn. Every time
Abbatoir feedback If you are sending animals (cattle or sheep) direct to slaughter, any livers condemned, and the reason they were condemned, will be detailed on the kill sheet. Every time
Liver fluke antibody test (blood sample)

Cattle and sheep develop antibodies to liver fluke within a few weeks of being infected for the first time. Although these antibodies give no protection to the animal, we can use them to show that an animal has been infected.

This is the test that will detect liver fluke earliest after infection, but as the antibodies last for months, they will still be present after successful treatment.

Best used at the beginning of the fluke season.

As this test detects the presence of liver fluke the soonest after infection (i.e it can detect fluke at the early immature stage), it is best used at the beginning of the fluke season to detect when the infectious stages (metacercaria) are starting to appear, and therefore, the risk of infection for cattle and sheep is starting.

As antibodies can last from the previous fluke season in adult animals, this test should be targeted at first grazing season animals (lambs are easiest) grazing known fluke risk areas.

Once they test positive for fluke antibodies

a) there is a risk to all animals grazing those areas
b) there is no point in repeating this test in the same animals, as they will remain positive for a long time.

The results will not tell us how many liver fluke are there, only that the animal has met a fluke.

Coproantigen test (dung sample)

This test is absolutely specific to Fasciola hepatica (the liver fluke) as it looks for secretions from the liver fluke in the faeces of the host animal. In field situations it can detect fluke infections from around 5 - 6 weeks after infection. Coproantigen levels drop off quickly once the liver fluke are removed, so a positive result means there is active infection.

Routine sampling, at any time during the season. As this test is via a dung sample it is easy to use. The test detects active fluke infections from 5-6 weeks after infection, with an increasing “score” as the number and size of fluke present increase.

NB As the test measure secretions from the fluke, a large number of smaller fluke will give a similar result to a smaller number of larger fluke.

This test can be used any time during the season, preferably after a positive antibody test has shown the fluke challenge has started. Ideally 10 samples should be collected from the group and tested individually (pooling samples for coproantigen testing can give misleading results). This will give us an indication of

a) how many animals in the group might be infected
b) the level of infection in the individual animal.

Fluke egg detection (dung sample)

This detects the presence of egg laying adult fluke. These will already have been present in the liver for 8-10 weeks before they mature and start producing eggs.

Although the fluke will produce thousands of eggs, they are released from the gall bladder into the gut intermittently, so not every faeces sample from an infected animal will have eggs in.

As the eggs are held in the gall bladder, they can continue to be found in dung samples for up to 3 weeks after the fluke have been removed.

Best used as a pooled test, where multiple samples from a group are mixed together and analysed once, but not in the early part of the fluke season as it detects the presence of adult, egg-laying fluke. A negative result does not mean there are no fluke present, just that there are no adult fluke present.

As a dung sample is used for the test, it is easy to use, but it does rely on a lab technician correctly identifying liver fluke eggs. Rumen fluke eggs are very similar to liver fluke eggs, and both types of eggs can be easily confused for one another.