Sheep farmers urged to be alert as worm infections rise

Sheep farmers are being encouraged to watch out for Haemonchus contortus infections – commonly known as Barber’s Pole worm –.after a rise in incidence.

The Sustainable Control of Parasites in Sheep (Scops) group says recent testing has indicated increased activity and possible cases of haemonchosis (the disease associated with haemonchus infections) appearing further north in the country.

While the reasons aren’t fully understood yet, climate change and warmer weather conditions allow the parasite to survive even in winter.

See also: Haemonchus vaccine given UK funding aid

Haemonchus can have devastating consequences for flocks. To help with effective parasite control, Scops stresses the importance of accurate diagnosis and calm, evidence-based decision-making. 

What is Haemonchus contortus? 

Haemonchus contortus is an abomasal bloodsucking roundworm.

Adult haemonchus worms, and worms approaching adulthood (L5), have the ability to remove large quantities of blood (0.05ml/day) from their host.

A sheep carrying 5,000 H contortus may lose 250ml of blood a day.

This, Scops highlights, combined with blood loss from the mucosa, produces acute disease caused by rapid anaemia (pale gums and eyelids).

It can also lead to bottle jaw (swelling under the jaw), lethargy, weight loss, and in advanced cases, sudden death. 

As few as 500 adult worms can cause disease, though the presence of haemonchus eggs in a faecal egg count (FEC) does not always indicate haemonchosis (clinical disease). 

Nerys Wright, Scops technical adviser, said: “We’re seeing more interest and investigation into this parasite, which is positive, but we must avoid jumping to conclusions or reverting to blanket treatments, especially in adult ewes that could undermine responsible and sustainable parasite control.”

Diagnosing haemonchus

Farmers are encouraged to work closely with their vets and advisers and to take a test-first approach, including carrying out an FEC to determine the strongyle count. 

A high strongyle count (several thousand eggs a gram – EPG) is indicative, but cannot confirm the presence of haemonchus.

Species testing, such as peanut agglutinin (PNA) staining must be submitted via your vet and identifies the proportion of strongyle eggs that are haemonchus.

This test is available through the Animal and Plant Health Agency and is currently discounted at £20 a sample. 

Famacha scoring is a useful tool for assessing anaemia in potentially affected animals, and farmers can evaluate the colour of the lower eyelid (conjunctiva) using a scale from 1 (red, not anaemic) to 5 (white, severely anaemic).

Post-mortems can identify a range of health issues. Unlike other roundworms, adult haemonchus worms can be easily seen by eye in the stomach.

Combined with signs such as pale carcases and weight loss, this can confirm the presence of disease.  

Treatment

When it comes to treating infections, Ms Wright explained product choice is crucial.

“We have limited resistance data for haemonchus in the UK, so using newer or narrow-spectrum actives without confirmed need could lead to problems in the future,” she added.

Treatment decisions should be based on diagnostics and tailored to the farm’s history of product use, as well as other parasite burdens and treatments.