Ostertagia In Cattle

Barber's Pole Worm In Sheep

Barber’s Pole worm is considered an important internal parasite of sheep and goats worldwide, causing significant production losses in many countries. It is a major problem in certain sheep areas of Australia, especially Northern NSW and in Queensland, but it also occurs in higher-rainfall and coastal zones in all states.

Populations can build quickly because of the worms' huge egg output and because they are large, blood-sucking worms, the clinical signs, including severe anaemia and death, can occur rapidly. Regular monitoring using worm egg counts (WECs) when conditions are favourable (particularly wet summers) and strategic use of effective drenches is essential to prevent major production losses.

Haemonchus contortus 

The Barber's Pole worm (BPW), Haemonchus contortus, is quite long (20 to 30 mm) and clearly visible. Only the adult female has the characteristic 'barber's pole' appearance due to the pink (blood-filled) intestinal tract of the worm twisted around the paler reproductive tract. The male worm is smaller (around 15 mm) and pale pink.

Females are prolific egg layers, laying up to 10,000 eggs per day. BPW eggs require warm, moist conditions to hatch. Once hatched, however, they develop into tough larvae that can survive for months on pastures before being ingested by grazing sheep, where they then grow into blood-sucking adults.

Adults can become arrested or inhibited inside the sheep for varying periods. They resume activity when environmental conditions become more favourable or when ewes have lowered resistance around lambing time.

Clinical signs   

Because they are blood-sucking worms, clinical signs include:

• Anaemia

• Lethargy

• Failure to gain weight

• Submandibular oedema (bottle jaw)

• Collapse

• Death

Diagnosis  

The only accurate way to diagnose worm infections before productivity losses have occurred is to conduct a WormTest (worm faecal egg count). A larval culture is usually recommended in areas where barber's pole worm is common and in other areas, under wetter than normal conditions, when barber's pole worm can become a problem.

A Haemonchus Dipstick test measures blood in the dung, usually the result of the Barber's Pole Worm that excretes blood and causes the bowel to bleed. If sheep have recently picked up a large burden of immature worms then eggs won't have been laid yet and therefore won't be detected by the Worm Egg Count.

Treatment   

Drench resistance is a major issue for BPW control due to over frequent drenching programs in the past. There is now widespread resistance to almost all drench groups. For example, in Northern NSW resistance to moxidectin is reported from well over half of recent drench resistance tests.

The choice of treatment will depend on:

• the size of the worm burden as determined (worm egg count)

• what other worms are also present and in what proportion

• the drench-resistance status and which drenches are effective on your property (drench test)

• the likely worm-risk over the next few months and the length of protection you are seeking

• the likely level of worm contamination on your pastures

• the class of sheep and their susceptibility to worms

• the last drench group/s you used on this (and other) mobs

• the withholding period and export slaughter interval of drenches you might use

Combination drenches, such as Zolvix, may be an effective choice as the first summer drench for many sheep producers, especially those who aim to rotate away from the mectins at this time. While young sheep should be drenched in summer, it is more effective to drench adult sheep in autumn when there is some development of worm eggs and hence dilution of resistant worms present in sheep.

Prevention  

The negative impact of this worm can also be reduced through grazing management strategies and by using one of the integrated worm control programs, which have been developed for different regions across Australia. See the WormBoss website for more details on your region.

Grazing strategies include moving sheep onto a clean pasture after drenching, spelling pastures, rotational grazing, and alternating sheep with cattle on pastures. Breeding sheep that have more immunity to worms and improving nutrition so that sheep are better able to handle worms are other useful control measures.

The good news is that a vaccine against Barber's Pole Worm has been developed and was registered for use in sheep of all ages in December 2015. As its availability increases, the vaccine will be very useful for areas where BPW occurs most seasons and where drench resistance is a problem.

Contributors: Dr Julia Adams BVSc

By Provet Resident Vet - Last updated 1 February 2015