Watch Out For Summer Worms

Sheep producers in South Australia are well experienced in recognising and treating signs of worm infestations in their sheep, but one particular parasite is becoming more common that may trip you up!

Barber’s Pole Worm (Haemonchus contortus) (BPW) is a very nasty worm that does not behave as the others do! The most common sign of a problem with Barber’s Pole worm is when lambs in good condition start dying in mid-summer, with no signs of scours, usually about 2- 3 weeks following summer rain.

Deaths in ewes, rams or wethers can occur, but these are rare in my experience in SA - unfortunately it is usually the best lambs, and especially if they have been in a confinement feeding situation over summer, as will be the case for many sheep in SA in the 2018/19 season in semi-arid (Mallee, Yorke Peninsula & West coast) regions.

Although deaths may appear to commence suddenly, lambs may have appeared to have been weaker or lacking energy prior to this. This is because the parasite sucks blood from the sheep and causes profound anaemia (blood loss). If the membranes in the eyelids of sick lambs or ewes is done they will appear to be white, rather than the usual pink colour. Another sign (more visible in ewes) is the development of “bottle jaw” (fluid swelling under the throat) –again caused by blood loss.  

This parasite is one of the most prolific egg layers known, with a single adult worm able to produce 10,000 eggs per day. Total worm egg counts in affected mobs of sheep can be 20-30,000 eggs per gram. Beware though – immature worms can kill sheep and the worm egg count could still be lower at that time. This parasite also lives in the 4th stomach (abomasum) of the sheep, so it will not be visible in the intestines. Adult worms are about 1- 2 cm long and have a red and white striped appearance; immature worms are shorter and red coloured.

Signs of barber’s pole worm 

  • Sporadic (occasional) losses of lambs with numbers rising – usually late January to March , 3 weeks after significant summer rain
  • No scours, sheep seem “weak, lethargic”
  • No obvious abnormalities if you open up a freshly dead sheep - unless you look in the 4th stomach, where BPW are easily visible, usually in large numbers.

What to do?

If you suspect Barber’s Pole Worm in your flock you should immediately get a worm egg count done on a manure sample from that mob. If any freshly dead sheep are available an autopsy is highly recommended. You can even do a basic autopsy yourself and send photos to your vet or PIRSA Veterinary Officer.

Once BPW has been diagnosed you should drench all affected mobs immediately to avoid further losses and loss of production. Fortunately worm drench resistance has not been reported in the semi-arid parts of SA very often, although some drenches are more specific and will have longer duration for this parasite than others - contact your livestock consultant, vet or PIRSA District Veterinary Officer for further advice.

By Jeremy Rogers, Senior Veterinary Officer, PIRSA