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Barber’s pole worm in winter, non-seasonal and Mediterranean rainfall areas

Bottle jaw in a sheep with a severe barber's pole worm infection.
Bottle jaw in a sheep with a severe barber's pole worm infection.

By Deb Maxwell, ParaBoss Operations Manager

September 2015

 

Barber’s pole worm (Haemonchus contortus) occurs in all sheep production areas of Australia, even in arid areas. With the introduction of the Barbervax® vaccine it is timely to clarify the areas of Australia in which it is recommended for use.

In the higher rainfall sheep-production areas of northern NSW through to north Queensland, barber’s pole worm can be relied upon to present the risk of haemonchosis (the clinical disease caused by barber’s pole worm) for at least four months every year.

In high summer-rainfall regions, the Barbervax vaccine, released in 2014, provides a new and effective method of control.

Barber’s pole worm also occurs in winter, non-seasonal and Mediterranean rainfall areas, but disease (‘haemonchosis’) is generally sporadic and short-lived. On most properties, it does not occur every year, and generally, one effective treatment will sort it out. However, when it does occur, producers can be caught out with unexpected deaths in their flock.

In winter, non-seasonal and Mediterranean rainfall areas, the need for the Barbervax vaccine is low and infrequent; it is unlikely to be a cost-effective option on most properties.

On any property where the Barbervax vaccine is being considered, be aware that it is not a ‘treatment’ for sheep with haemonchosis. It should be used in a preventative program.

How can producers in southern Australia be prepared for barber's pole worm?

The vaccine suits areas where there is a high risk for many months each year. In those areas, the initial priming doses given over 2–3 months pay off over successive months and years of an animal’s life (as immunity to barber’s pole is generated with the first dose in each of the following years).

In most of southern Australia (winter, non-seasonal and Mediterranean rainfall areas) where barber's pole worm is not a problem every year, sheep producers can best be prepared by understanding the conditions that lead to unusual increases in barber’s pole worm and by regularly monitoring the worm egg counts of their sheep in high risk periods.

In southern NSW, Victoria, Tasmania and South Australia, haemonchosis generally occurs in mid-summer to late-autumn, and occasionally into winter, after wetter than usual conditions. In Western Australia, the main risk periods are early to mid-summer (weaners), and late autumn into winter (lambing ewes). In all locations, irrigated pastures and coastal areas also present a higher risk due to the combination of warmth and moisture.

The first sign of haemonchosis that an unprepared sheep producer usually sees is dead sheep. However, barber’s pole worms don’t kill sheep suddenly, it usually takes at least 2–3 weeks, and generally a lot longer.

Why are dead sheep often the first sign of haemonchosis?

Unlike scour worms, the signs of barber’s pole worms are not easily visible from a distance. There is no scouring and obvious weight loss, so the signs are not apparent on routine in-paddock checks of the flock.

Instead, barber’s pole worms suck blood; this causes anaemia. When the worm population is high enough for long enough, the sheep can’t replace the red blood cells as fast as they are being removed. Eventually, there are not enough red blood cells to transport oxygen around the body and the sheep collapses and dies. Surprisingly, many sheep are eating and often appear quite well until just before they die.

How can haemonchosis be diagnosed at the right time?

The aim is to diagnose haemonchosis before it becomes advanced and is causing production loss and death. When the season is wetter than normal, conduct regular worm egg counts each 4–6 weeks during risk periods. Counts above 1000 epg indicate that sheep should be drenched for barber’s pole worm, to prevent the build-up of massive numbers of barber’s pole worm larvae on the pasture.

In advanced cases (typically where monitoring has not been in place), sheep can be noticeably anaemic—the inside of the lower eyelids are pale. They can have ‘bottle jaw’ where there is swelling under the jaw (but not all affected sheep will have this), and sheep can collapse (and die) when being mustered.

Note that similar signs can occur with a liver fluke infection and with Mycoplasma ovis (formerly called Eperythrozoon ovis), a blood parasite that also occurs during wetter than normal summers. However, these don’t result in a high worm egg count.

How should barber’s pole worm be treated?

An effective short-acting drench is usually all that is needed, though on highly contaminated pastures and where green pastures persist during warm conditions (perennial pasture or irrigation), a persistent product may be warranted. Follow up with a worm egg count in a further 4–5 weeks after a short-acting drench (or 9 weeks after closantel). If barber’s pole is a significant problem every year, long acting drenches may be necessary at particular times, and this should be planned as part of the annual worm control program.

Knowing which drench actives are effective may be difficult, as even properties where Drench Resistance Tests have been conducted may not have results specific to barber's pole worm. The narrow spectrum active, closantel, which can provide at least 4 weeks protection, is still highly likely to be effective in southern Australia. In contrast, most barber’s pole worm populations in northern Australia have some resistance to closantel. Moxidectin also has a protective period against barber’s pole worm, and may be an option where both barber’s pole worm and scour worms are present. However, it is important to check for resistance before moxidectin is used.

If severely affected sheep collapse during a muster, leave them behind, but go back and drench them. Don’t use an organophosphate drench (i.e. Rametin® or Combat®) on severely affected sheep.

Summary

In the non-summer rainfall areas, sheep producers should be alert to the seasonal conditions where there is a barber’s pole worm risk, and when these occur (such as when summers are wetter than normal), test worm egg counts each 4–6 weeks. If counts rise above 1000 epg, sheep should be drenched with an effective product against barber’s pole worm, with a follow up worm egg count. As always, consult a local animal health advisor if more specific information is required.