PC Sheep Liver Fluke2020 FINAL

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Understanding Liver Fluke in Sheep Flocks

Detecting liver fluke in sheep flocks A faecal egg count (FEC) can test for the presence of adult fluke in sheep*. This test cannot detect if there are immature liver fluke infections in animals, and the number of eggs produced by adult fluke fluctuate, so a negative FEC does not guarantee the absence of liver fluke. The season, history of liver fluke infection on farm and clinical signs should be considered before a diagnosis of liver fluke infection is ruled out when the FEC is negative. This is especially important during seasons when the FEC test becomes unreliable (Table 1) . For good quality faecal egg counts, it is essential to obtain fresh faecal samples and ideally the samples should reach the laboratory within 24 hours. Pooled samples can be more cost effective but are less sensitive at detecting low levels of infection. For pooled samples, equal quantities of faeces should be taken from 5-15 animals per management group.

Winter to spring

Summer to autumn Late autumn to winter

Fluke life stage likely to be present Faecal egg counts expected (given as eggs per gram [epg])

Mixed immature and adults likely

Adult flukes likely

Immature flukes likely

Higher FEC >100 epg

Low FEC Eggs unlikely

Lower FEC <100 epg

Subacute to chronic disease risk

Sheep clinical signs

Chronic disease risk

Acute disease risk

Table 1: Liver fluke life stage and expected FEC

A coproantigen ELISA or serum ELISA can also be performed and may detect immature fluke infections before eggs are seen in a FEC test. The coproantigen ELISA is a test which detects evidence of early liver fluke infection in faecal samples before the parasites are mature enough to produce eggs. A serum ELISA can determine if the animal has developed antibodies to liver fluke infection. However, this test cannot distinguish between a current or a previous infection. Treating animals at risk of acute/subacute liver fluke infection on farms with a history of fluke infection is advisable. The ideal time to treat can vary depending on the weather conditions from year-to-year. The annual DAFM liver fluke forecast, issued in autumn each year (http://www.agriculture.gov.ie) can help identify an emerging high-risk period when treatment is indicated. Years with mild temperatures and high rainfall during summer can result in a high risk of liver fluke infection. Taking FECs across the year can help identify the best time to use drug treatments on farm. *A liver fluke FEC may also detect rumen fluke eggs. Rumen fluke infections in sheep do not always require treatment, but it is important to note that the treatment for rumen fluke infection differs to that required for liver fluke. Controlling liver fluke on farm Most control programmes rely heavily on flukicidal drenches to kill fluke once animals are infected and ideally before they can cause serious disease. Different drugs are effective against differing stages of liver fluke infection (Table 2). It is important to select a product with the appropriate active compound given the time of year and stage of infection that requires treatment. In all cases meat withdrawal periods must be strictly observed.

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