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Monepantel (Zolvix®) resistance confirmed in goats in NSW Australia (updated 27.6.14)
Resistance of worms in goats to monepantel (Zolvix®, Novartis) was recently confirmed on a farm in the central west of New South Wales. As far as I know this is the first and only case of confirmed resistance to monepantel in Australia.
Resistance to this drench on goat farms in NZ was reported in 2013, 4 years after the ‘world launch’ of monepantel (MPL) in that country in autumn 2009.
The property in NSW breeds their own goats and sometimes imports goats from other farms.
MPL, which is only registered for use in sheep, had been used on the farm shortly after the drench was available in Australia (spring, 2010). On the first occasion the drench was used at the sheep dose rate. Thereafter a higher rate was used when the farmer learnt more about the way goats metabolise drenches.
The owner resorted to MPL because of apparent control failures when using a variety of other drenches to control worm problems during a particularly wet year.
To his credit, this goat producer does frequent worm egg counts (WECs) to monitor worm burdens and to check the efficacy of drenches. Across Australia, probably less than 10% of sheep and goat producers do this. It was during routine monitoring in 2012 the producer discovered signs of reduced efficacy with MPL
The owner sought advice from Dr Belinda Edmonstone, the District Veterinarian at Forbes NSW (http://centralwest.lls.nsw.gov.au/) regarding the positive WECs in some goats after the quarantine drench. We discussed the case together, and then invited veterinarians from Novartis Animal Health (NAH) to be involved.
Following standard protocols, Belinda and one of the NAH vets set up a faecal worm egg reduction test (WECRT, aka ‘DrenchTest’) on the farm. There was a treatment group that received Zolvix® at 1.5 times the sheep dose rate, and a group of untreated controls. Faecal samples were divided and sent to the NAH research facility in Sydney as well as NSW DPI’s State Vet Lab at Menangle (outer Sydney), for egg counting and larval cultures.
Following are the results of the DrenchTest, conducted in spring 2012:
Haemonchus spp (barber’s pole worm): 100% reduction in WEC post treatment.
Trichostrongylus spp(black scour worm/stomach hair worm): 92 to 97% reduction.
Teladorsagia spp (small brown stomach worm): the WECs in the untreated controls were too low to be conclusive, but the number of eggs left after treatment gave cause for concern.
Confirmation by way of slaughter study was the next step. Goats were monitored on-farm until WECs were high enough, which took some time. This and other issues delayed the study somewhat. When counts were satisfactory, faecal samples were collected and sent to the NAH research facility for culturing and subsequent artificial infection of sheep.
Below are the results of the slaughter study in sheep, comparing total worm counts of those treated with Zolvix – at the recommended dose rate for sheep – with counts for sheep that were left untreated.
Slaughter study results
Haemonchus contortus (barber’s pole worm):susceptible (i.e. MPL was highly effective).
Trichostrongylus colubriformis (black scour worm): emerging resistance.
Teladorsagia circumcincta and trifurcata (small brown stomach worm): severe resistance.
This appears to be the first report in Australia of confirmed* resistance to monepantel. (*WECRT+slaughter study)
A report to be published in a peer-reviewed scientific journal is planned.
The comments I made regarding the NZ report of monepantel resistance are generally relevant. Rather than repeat them here, see:
The point of this WormMail? This post will be worthwhile if it somehow puts producers and their advisors on alert – and results in greater diligence in looking after the drench actives we have.
There are goat farms in NZ and AU with resistance to all broad-spectrum anthelmintic products currently on the market (with the exception of – as far as we know – Startect (the derquantel part of it anyway)).
These include organophosphates (in AU), benzimidazoles, levamisole/morantel drenches, and the macrocyclic lactones. As to the latter, Leathwick (1995) reported a ~ 1993 case in NZ where neither ivermectin, nor moxidectin (the most potent of the MLs in small ruminants), appreciably reduced worm egg counts after treatment. (I understand moxidectin was launched in NZ 1991, ~3-4 years before Australia). No drench is immortal (but we can affect their life span).
For the Australian farm in question here, it seems possible, for example, that the MPL-resistant worms were imported onto the property and/or home-bred.
So, consider this: how good are your/your client’s quarantine / biosecurity practices??
And further, how good are your other practices? (worm egg count monitoring? regular drench efficacy checking? maintaining worms in refugia? grazing management? promoting worm-resistance in animals? nutrition? and so on…..
Its not just about goats. Sheep are not far behind. And in recent years we have been reminded that resistance of cattle worms to drenches is definitely an issue as well.
Leathwick DM (1995). A case of moxidectin failing to control ivermectin resistant Ostertagia species in goats. Veterinary Record (1995) 36, 443-444.
Le Jambre LF et al (2005 ). Characterization of moxidectin resistant Trichostrongylus colubriformis and Haemonchus contortus. Veterinary Parasitology 128 (2005) 83–90. (This paper includes evidence of resistance to naphthalophos).
Scott I, Pomroy WE, Kenyon P, Smith G, Adlington B, and Moss A. Efficacy of monepantel against goat-derived parasite strains: the results of an egg count reduction test in goats and a slaughter study in sheep. International Sheep Veterinary Congress, New Zealand, 2013.
Scott, I., Pomroy, W.E., Kenyon, P.R., Smith, G.,Adlington, B., Moss, A., Lack of efficacy of monepantel against Teladorsagia circumcincta and Trichostrongylus colubriformis, Veterinary Parasitology (2013). ( Regarding the goat farm which is the subject of this paper: I believe the owner, having exhausted all other options, is now using Startect (derquantel+abamectin)).
2010-06-11 (updated 2014-06-27)
Added comments (2014-06-27:
Where to from here?
In Australia first confirmed reports of resistance to new sheep drenches occur about 4 years after coming onto the market. There are exceptions.
We can influence how long drenches ‘live’. Best practice sheep worm management is the way to go. WormBoss – wormboss.com.au – tells you how, and the general principles apply to other grazing livestock.
Following is an outline, in no particular order. Go to WormBoss for more information.
Keep resistant worms out. Current best practice for quarantine drenching (Australia): use Zolvix concurrently with at least three other unrelated broad-spectrum actives.
Rotate drenches and consider combinations. Use Zolvix in a rotation with other unrelated drenches (or combinations of drenches) known to be effective on the property.
Use effective drenches: drenches that have been tested on-farm and shown to be effective.
Drench at the right time
Grazing management: to reduce exposure of sheep to worms, and improve nutrition.
Follow the right program for your region
Improve the resistance and resilience of your sheep to worms: through breeding, and ‘feeding’ (nutrition).
Maintain worms in refugia: don’t expose all or most worms on a property to a drench at the same time.
Summary of managing drench resistance: