Potential new threat in sheep worms

Haemonchus contortus or barber’s pole worm has been diagnosed as the cause of death of a four-year-old ewe in Kilkenny Regional Veterinary Laboratory, which is operated by the Department of Agriculture, Food and the Marine (DAFM).

The ewe was submitted from a farm in county Kilkenny, with a history of pale gums and conjunctivae (potentially indicating significant blood loss). Numerous Haemonchus contortus worms were found in the abomasum (fourth stomach) of the ewe. A faecal sample from the ewe contained an estimated 50,000 Haemonchus contortus eggs per gram of faeces.

Haemonchus contortus most commonly affects sheep and goats, but can also affect cattle. It is often called the barber’s pole worm, due to its resemblance to a red and white barber’s pole when the intestine is full, following a blood meal.

Even much lower worm burdens can cause enough blood loss to cause disease

The red intestine spirals round the pale uterus of the female giving the barber’s pole effect. The adult worms have a piercing lancet which facilitates extraction of blood from the blood vessels of the abomasum.

The host becomes ill due to the blood feeding activities of the adult and developing larvae. Each worm can remove about 0.05ml of blood per day, so sheep and goats with 5,000 worms may lose about 250ml daily.

Even much lower worm burdens can cause enough blood loss to cause disease. Typical signs of infestation include paleness of gums and conjunctivae, swelling under the jaw (bottle-jaw), increased rate and depth of breathing, and an increased heart rate.

Clinical signs can also include sudden death in very acute cases, and ill-thrift in chronic cases. It is important to note diarrhoea is not a typical feature of the disease.

There is little effective immunity to Haemonchus contortus worms. Unlike the case with other parasitic diseases, adults are also at risk of haemonchosis.

Control and prevention relies on regular faecal egg counts, pasture management and strategic anthelmintic use.

The larvae develop more rapidly and successfully, and have better survivability over winter, at warm temperatures

In temperate climates like Ireland has, Haemonchus contortus does not tend to survive the winter in large numbers on pasture. The principal way in which it survives in flocks over winter is through the persistence of larvae in a hypobiotic (dormant) state in the gut of the host. This feature lends itself to the development of anthelmintic resistance in Haemonchus contortus worms, and so resistance is a common feature in flocks affected by the parasite.

The larvae develop more rapidly and successfully, and have better survivability over winter, at warm temperatures. Accordingly, the disease is much more prevalent and causes greater losses in tropical and subtropical areas than in temperate climates.

With the prospect of warmer temperatures and milder winters in Ireland due to climate change, it is to be expected that the prevalence of haemonchosis will increase in the years ahead, and that outbreaks causing substantial losses will become more common.

Farmers are advised to contact their private veterinary practitioner to discuss diagnosis, treatment and control in greater detail if they suspect haemonchosis in their flocks or herds. Regular updates on animal health issues and information on animal health can be found on the Animal Health Surveillance website here.