Extended fluke challenge

Set up by Elanco in response to issues identified by FALF in 2015's wider liver fluke awareness campaign, the surveillance farms see industry experts and the farms' own vets working closely together to test, monitor and help manage a sustainable approach to liver fluke control on each farm.

"The liver fluke lifecycle is dependant to a large extent on the weather," said Matt Colston, veterinary surgeon at Elanco. "The mild wet autumn and winter weather allowed the mud snails to remain active well into and through the winter.

"As long as the snails are active, more cercaria are released, increasing the metacerarial numbers on pasture, so increasing the risk of disease in grazing animals. This varies from farm to farm, and also depends on there being suitable habitats for the mud snail (Galba truncatula) which is the intermediate host for the liver fluke. Understanding this link between weather and the fluke challenge - and the need to act accordingly - is vital."

"For our five farms, where there is a fluke challenge, the level of challenge has been maintained or is increasing, with the risk of acute or sub-acute disease still present," confirms Matt Colston.

"In these circumstances treatment with an active effective against early immature fluke is advisable. This would normally be triclabendazole, or closantel where triclabendazole resistance has been established."

Surveillance Farm results update

Farm 1: George Milne - Kinaldy Farm, Fife

In November 2015, lambs had shown evidence of early infection (6 testing positive to Copro-antigen, no fluke eggs present) so some were treated with Closantel. January samples therefore looked at treated and untreated lambs but also ewes:

Treated lambs:

• Copro-antigen - 3 positive, 7 negative

• Fluke egg detection - all samples negative

Untreated lambs:

• Copro-antigen - 4 positive, 6 negative

• Fluke egg detection - 2 positive, 8 negative

Ewes

• Copro-antigen -positive bulk sample

• Fluke egg detection - large numbers in bulk sample

What next? With treated lambs showing signs of early infection, untreated lambs chronic infection, and large numbers of fluke eggs in the ewe's bulk sample this suggests animals are still acquiring new infections, with untreated animals potentially having well established infections. All groups would benefit from treatment.

Farm 2: John Harrison - Croftheads, Dumfries & Galloway

Lambs

• November - Copro-antigen - 1 positive, 9 negative

• December - Copro-antigen - 7 positive, 3 negative

• January- Copro-antigen - 10 positive

Ewes (December)

• Copro-antigen -positive bulk sample

• Fluke egg detection - large numbers in bulk sample

What next? Mr Harrison's lambs had been showing an increasing level of infection from November 2015 to January 2016 and these samples were part of a Triclabendazole efficacy test. The Copro-antigen average increased after treatment suggesting, despite animals looking well due to the low/moderate challenge, that the treatment had not been effective. This shows the benefit of pro-active testing and all groups were then treated with Closantel.

Farm 3: Paul Capstick, Parkhouse Farm, Heversham, Cumbria

Lambs (December)

• Copro-antigen - 3 positive, 7 negative

• Fluke egg detection - 2 positive, 8 negative

Ewes

• Copro-antigen - positive bulk sample for the first time

• Fluke egg detection - large numbers in bulk sample for the first time

What next? With December lamb samples showing continued low/medium challenge and ewe bulk samples testing positive for the first time, January samples are being analysed to determine treatment options.

Farm 4: Carwyn Roberts, Garn Fach, Llanelli

Lambs were treated with Closantel in early November, subsequent samples taken were all negative.

December

• Copro-antigen - 5 positive, 5 negative

• Fluke egg detection - 10 negative

January

• Copro-antigen - 10 positive

• Fluke egg detection - 9 positive, 1 negative

What next? With December and January samples showing evidence of growing exposure and infection, and continued medium to high challenge, all groups would benefit from treatment.

Farm 5: Mr Peter Derryman, Peterhayes Farm, Honiton, Devon

Ewes (Nov & Dec)

• Copro-antigen - negative

• Fluke egg detection - negative

What next? Lambs are kept on low risk dairy pasture and all samples are Copro-antigen negative with no fluke eggs either which suggest no fluke challenge yet and no treatment needed.

"These results show the impact that weather can have on liver fluke levels and the need to stay alert to the challenge", advises Matt Colston. "I urge famers, including those in areas previously thought of as fluke-free, to learn from these surveillance farms and to consult with their vets and animal health advisers to establish similar control measures for sustainable liver fluke control if they have not done so already."

"The campaign has highlighted the need for better awareness of sustainable liver fluke management and for this to be translated into practical action, using the right product, at the right time on the right stage of fluke.

Understanding the tests available

With liver fluke growing through three development stages within the animal, and treatment needed for lambs and ewes, it is important to choose the right set of tests. Infection also depends upon the areas sheep have been grazing, so one group could have no challenge, whilst others are still at risk.

Fluke Antibody test - blood samples for anti-fluke antibodies will show the first signs of exposure to fluke.

Positive - indicates that lambs have already met a liver fluke challenge. However it does not tell us the level of that challenge, or whether it is likely to cause clinical disease, or decreased growth rates.

Negative - no exposure to liver fluke yet and no treatment necessary . Other groups on the farm could still be at risk, depending on the areas they have been grazing.

Copro-antigen - Specific for Fasciola hepatica, this test detects the presence of active liver fluke when the volume of "excretions" from the fluke pass a certain threshold.

Positive - indicates active liver fluke infection

Negative - No fluke, very low numbers, or fluke so small that their secretions do not exceed the threshold.

Fluke egg detection - Faecal Egg Count

Positive - egg laying adult fluke present. False positives can occur if rumen fluke eggs are mistaken for liver fluke eggs, or if all fluke have been removed but eggs are still being released from bile ducts and gall bladder.

Negative - no egg laying adult fluke present. (There could still be large numbers of immature fluke present) False negatives can occur because fluke eggs are shed intermittently, and the sample size/dilution factor may mean egg numbers are below the level of detection.