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Turning the Worm

Stephen Love, NSW Department of Primary Industries, Armidale NSW 2350

Posted Flock & Herd May 2015


There is no breaking news in this paper. Rather it is an overview of items relating to livestock parasitology that I think is worth repeating. Those who have been District Veterinarians for some time - and have their memories intact - will be au fait with much of this; those newer to the ranks may not.


Turning the Worm (TTW) was the name I gave to a newsletter, a more formal version of the more or less weekly WormMail, both of which I started up a little over 15 years ago. TTW has been incorporated into WormMail (WRML).

Turning the Worm is a twist on 'the worm turns' which refers to people, groups or things that, after being badly treated for a long time, suddenly and forcefully resist.

The worms we deal with can be a bit like that.


WormMail is a more or less weekly newsletter mostly on livestock parasitology. It has about 400 subscribers.

It also includes WormFax, a monthly summary of sheep WormTest (worm egg counting (WEC)) results from around New South Wales.

To subscribe to WormMail, email me or go to www.dpi.nsw.gov.au

Back issues can be found on the web at WormMailintheCloud wormmailinthecloud.wordpress.com


Another useful source of information is WormBoss.com.au. It is part of the ParaBoss suite which also includes FlyBoss and LiceBoss.

As a founding member of the WormBoss technical team, I am biased, but I think WormBoss is an excellent resource and deserves the description of 'Australia's national repository of information on best-practice sheep worm control'.

Farmers and those new to sheep parasitology should go first to the 'Your Program' section. There is also provision for on-line learning within all the 'Boss' websites.

Consider subscribing to the monthly ParaBoss News. Many District Veterinarians (DVs) contribute to this and indeed quite a few DVs directly or indirectly have contributed to the content on WormBoss. This is acknowledged in the foreword for each 'Your Program' that relates to NSW.


Playford and others (2014) published the results of a recent study of drench resistance in Australia. Data were analyzed from 390 worm egg count reduction tests conducted from 2009 to 2012.

Here, in the following graph, is a partial summary.

Graph of drench resistance
Figure 1. Percentage of tested sheep farms with drench resistance (Australia, 2009-2012)

Notes: BZ=benzimidazole, 'white'. LEV=levamisole, 'clear.' MPL=monepantel ('Zolvix', an 'AAD'. No resistance detected).The macrocyclic lactone (ML, 'mectin') drenches are: IVM=ivermectin, ABA=abamectin, MOX=moxidectin. BZ/LEV etc. are combination drenches. CLOS=closantel. *Less than 50 usable drench tests for this drench. 'Resistance' here means the worm egg count reduction after treatment was <95% for one or more of Haemonchus, Trichostrongylus or Teladorsagia species.


Novel actives monepantel (in Zolvix®, Novartis) and derquantel (in Startect® = derquantel + abamectin, Zoetis) were released in Australia in 2010 and 2014 respectively. New Zealand was the first country in which monepantel was released, in 2009.

Resistance to monepantel was confirmed in goats in New Zealand by Scott and others (2013). The first confirmed case in goats in Australia occurred in central western NSW (Love, 2014).

Resistance of Haemonchus in sheep was reported in Uruguay in 2015 (Mederos and others).

As derquantel on its own does not have innately high efficacy against all stages of all the important sheep worms, it is classed as a mid-spectrum drench, although it generally has higher efficacy than naphthalophos, for example, which is also classed as 'mid spectrum'. According to Little (2010), derquantel is 'less than 95% effective against Teladorsagia (=Ostertagia) circumcincta (adults and L4), L4 of H. contortus, and some large intestinal nematodes (Little and Maeder, unpubl. data). This being the case, derquantel in Startect relies on abamectin to an extent to achieve high efficacy. However, resistance to abamectin is now common, and sometimes this resistance is severe. In such cases Startect may not always achieve high efficacy.

All things considered, producers should regularly conduct DrenchChecks after using drenches, new or old, as well as DrenchTests (worm egg count reduction test) every 2-3 years.


This has received greater attention in Australia in recent years. Results of surveys from Victoria and Western Australia are summarized in the graph below.

Graph of resistance WA and Vic
Figure 2. Resistance of cattle roundworms to drenches in Victorian and Western Australian trials: percentage of farms with efficacy less than 95%

Notes: 'Efficacy'= % worm egg count reduction (WECR) after drenching. Victorian trial: Rendell D, 2010.Western Australia trial, 2010-2011, reported by Cotter J and others, 2015. Ost=Ostertagia Coo=Cooperia sp. BZ=benzimidazole, LEV=levamisole, ML=macrocyclic lactone. Oral formulations were used, except injectable ivermectin in WA trials. WECR less than 95% indicates possible resistance. In the WA study, there were indications that ivermectin pour-on (not shown in graph) was less efficacious than ivermectin injectable.


Leathwick and Miller (2013) reported results of a trial conducted in cattle on 14 farms in New Zealand in which they studied the effect of route of administration on efficacy. The worm populations were comprised mainly of Cooperia, with variable degrees of macrocyclic lactone resistance. Moxidectin oral was more effective than moxidectin given by either the topical (pour-on) or injectable routes. See figure 3.

Also, efficacy of the oral drench was less variable than the others. Low drench efficacies were invariably against Cooperia (C. oncophora). All treatments in this study were effective against Ostertagia.

Graph of average drench efficacy
Figure 3. Route of administration and drench efficacy.


In October 2014 'Barbervax' vaccine had a restricted release in the New England region of NSW providing an alternative to drench-based control. It is the world's first sheep worm vaccine, and the first vaccine for a gut-dwelling worm parasite of livestock. Barbervax is the result of research in Scotland by the Moredun Research Institute and, more recently, collaboration with the Department of Agriculture and Food in Western Australia (Besier and others, 2014).

Barbervax is currently registered for use in lambs. It is given as a series of 5 subcutaneous injections of 1 ml, at approximately 6-week intervals to cover the season with a significant risk of haemonchosis; generally December to April in the NSW Northern Tablelands.

For more information see Besier and others (2014), and the Barbervax website: http://barbervax.com.au/ .


  1. Besier RB, Smith D, Dobson R and Kahn L, 2014. Barbervax® a new approach to barber's pole worm control. In WormBoss.com.au. Retrieved 9 March 2015 from www.wormboss.com.au
  2. Cotter JL, Van Burgel A, Besier RB. Anthelmintic resistance in nematodes of beef cattle in south-west Western Australia. Vet Parasitol 2015:207(3-4):276-84
  3. Leathwick DM and Miller CM. Efficacy of oral, injectable and pour-on formulations of moxidectin against gastrointestinal nematodes in cattle in New Zealand. Vet Parasitol 2013:19(3-4):293-300
  4. Little PR, Hodge A, Watson TG, Seed JA, Maeder SJ. Field efficacy and safety of an oral formulation of the novel combination anthelmintic, derquantel-abamectin, in sheep in New Zealand. NZ Vet J 2010 58(3),121-129
  5. Love S, 2014. Monepantel (Zolvix®) resistance confirmed in goats in NSW Australia. WormMail newsletter, June 11, 2014. Retrieved March 2015 from wormmailinthecloud.wordpress.com
  6. Mederos AE, Banchero GE, Ramos Z. First report of monepantel Haemonchus contortus resistance on sheep farms in Uruguay. Parasit Vectors 2014 7(1):598. Retrieved January 2015 from www.ncbi.nlm.nih.gov
  7. ParaBoss paraboss.com.au
  8. Playford MC, Smith AN, Love S, Besier RB, Kluver P and Bailey JN, 2014. Prevalence and severity of anthelmintic resistance in ovine gastrointestinal nematodes in Australia (2009-2012). Aust Vet J 2014; 92: 64-71
  9. Rendell DK. Anthelmintic resistance in cattle nematodes on 13 south-west Victorian properties. Aust Vet J 2010; 88: 504-509
  10. Scott I, Pomroy WE, Kenyon PR, Smith G, Adlington B, Moss A. Lack of efficacy of monepantel against Teladorsagia circumcincta and Trichostrongylus colubriformis, Vet Parasitol 2013;198(1-2)166-171
  11. WormBoss www.wormboss.com.au
  12. WormFax: www.dpi.nsw.gov.au
  13. WormMail: www.dpi.nsw.gov.au
  14. WormMailintheCloud wormmailinthecloud.wordpress.com


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