Warning as parasite spreads due to changing weather

Testing suggests Haemonchus contortus, or Barber’s pole worm, is becoming more prevalent in the UK as weather patterns change, vets have warned.

The Sustainable Control of Parasites in Sheep (SCOPS) group said recent testing suggests an increase in cases of Haemonchus infection, with the parasite appearing further north.

Farmers are being encouraged to familiarise themselves with signs of infection and regularly check their sheep.

Vet Gina Rigby from Cross Counties Farm Vets in Northamptonshire, part of the VetPartners group, said:

“Historically, if we had very cold, harsh winters, a lot of the Haemonchus larvae would be killed off, but now we’re finding that they’re overwintering – both on pasture and in the ewes – which means we’re seeing infection earlier in the year than we were before.”

What are the symptoms? 

Haemonchus is different from other gastrointestinal worms and, as such, it causes different symptoms.

“Haemonchus is a blood-sucking worm which can cause anaemia, and unless a sheep has a mixed infection with other gastrointestinal worms, it doesn’t cause scour,” Gina adds.

“This means sheep farmers are often caught out by it because they’re not seeing the classic signs of worms, like mucky back-ends, on their sheep.”

Symptoms of infection depend on whether the sheep is suffering from acute, sub-acute, or chronic infection.

“Acute infection is caused by an animal ingesting a lot of infective larvae in a very short period of time, and the signs include sudden death, rapid breathing, and pale mucus membranes which can be seen by looking at the inside of the lower eyelid,” she explains.

“Sub-acute infection isn’t always as obvious, and often farmers get this confused with liver fluke, because it causes bottle jaw (swelling under the jaw), while chronic infection presents as more of a failure to thrive with weight loss, poor body condition, and lethargy – along with the signs of anaemia.”

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Monitoring for Haemonchus

To monitor for Haemonchus, Gina recommends looking out for clinical signs of infection, FAMACHA scoring, worm egg counting, and carrying out a post-mortem examination on any dead animals.

“FAMACHA scoring is a colour chart to compare with the colour of the membranes of the lower eyelid to assess for anaemia caused by Haemonchus; it’s relatively easy to do when you’re already running animals through the race for other reasons,” she adds.

“Worm egg counts are also useful to identify the presence of worms, however ‘in house’ counts can’t easily differentiate Haemonchus from other worm species, so if you suspect you’ve got a problem, you can send a sample off to the lab for worm species identification.”

If Haemonchus is identified, speak to your vet to discuss an appropriate treatment plan.

“Finding Haemonchus in a sample doesn’t necessarily mean clinical disease is present on your farm,” she adds.

“Speak to your vet about treatment – both in terms of product choice and which animals need it, or whether vaccination might be an option on your farm.”

Perfect storm for worms

A SCOPS update also warned that the combination of earlier dry conditions and recent rainfall could create a perfect storm for increased worm challenges on pasture.

Nerys Wright, technical adviser for SCOPS, urged farmers to be extra vigilant in monitoring parasite burdens and lamb performance, including carrying out regular faecal egg counts (FECs).

However, she stresses that FECs should be interpreted alongside lamb condition and performance. 

After a prolonged dry spell, large numbers of immature worms may be present and cause clinical disease before a high FEC is detected. 

This makes visual assessment and consideration of nutritional status equally important in decision-making.

Poor grass growth

The earlier dry weather also limited grass growth on many farms, adding nutritional stress to lambs. 

“A lamb’s immune system is closely linked to its nutritional status,” explains Nerys. “Lambs under nutritional stress are less able to withstand a parasite challenge.”

Rebecca Mearns, parasitology vet lead at the APHA, adds that while some areas are now seeing high FECs following the rain, others remain low – highlighting the importance of testing and monitoring rather than assuming worms are the cause of poor performance.

“It’s essential to consider other factors like grass quality and availability,” says Rebecca. “Not all poor performance is due to worms, and blanket treatments can do more harm than good in the long term.

Funded testing 

SCOPS is also reminding farmers in England to take advantage of the DEFRA-funded Worming Treatment Check (WTC) scheme, available through the Animal Health and Welfare Pathway Review. 

In Scotland, a similar scheme supports farmers in preparing for sustainable farming, while Wales currently does not have a comparable programme.To benefit from funded testing, worm egg counts must be high enough to justify treatment. 

“The key message remains: check your FECs before undertaking the WTC to ensure the timing is right and the results are meaningful,” concludes Rebecca.

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