Resistance status of drench groups

The notes below are a general overview of the drench-resistance of worms to the drench groups listed at November 2012. They are based on reports from parasitologists, worm testing laboratories, research projects, drench manufacturers, and industry consultants.

However, the actual drench-resistance on your property for each drench is highly likely to be different to the overall state or region figures.

You should conduct a DrenchTest each 2–3 years and DrenchCheck-Day10s in between, to know the level of effectiveness of drenches on your property.

Knowing the resistance status on your property for individual actives will let you choose effective combinations—actives that are not highly effective alone can still be useful in a combination drench. 

Definitions for notes below

Number of properties affected: few = less than 10%; some = 10–50%; many = more than 50% of properties

Mixtures: not all groups in the product have broad spectrum activity against susceptible worms

Combinations: all groups in the product have broad spectrum activity against susceptible worms

Scour worms: black scour worm (Trichostrongylus colubriformis and T. vitrinus) and small brown stomach worm (Teladorsagia circumcincta)

Benzimidazole (BZ)

Many properties in Australia will have scour worms resistant to this group. Resistance by barber’s pole worm in summer rainfall regions is likely to occur on many properties. In other regions of Australia, resistance by barber’s pole worm is likely to occur on some properties. There is no reliable information on the resistance status of nodule worm. Resistance of liver fluke is likely to occur on very few properties in Australia. Resistance of Moniezia tapeworms has been reported in New Zealand, but there is no information for Australia. Unless resistance is severe, BZs may still be useful against roundworms when administered with unrelated actives in combination products or in a long-acting product (capsule) when given with an effective primer (see notes in Drench Decision Guide on the use of long-acting products).

Levamisole / morantel (LEV)

Many properties in Australia will have scour worms resistant to this group. Resistance by barber’s pole worm is largely restricted to summer rainfall regions where it is likely to occur on some properties. There is no reliable information on the resistance status of nodule worm. Unless resistance is severe, levamisole may still be useful when administered with unrelated actives in combination products.

Organophosphate (OP)

Few properties in Australia have scour worms or adult barber’s pole worm resistant to organophosphates. This group has variable efficacy (e.g. 70-90%) against scour worms and immature barber’s pole worm, and no activity against large bowel worms including nodule worm.

Salicylanilides/Phenols (SAL-P)

The activity of this group is restricted to barber’s pole worm and older stages of liver fluke. It has no activity against nodule worm and scour worms. Many properties in summer rainfall regions (but generally few properties in other regions of Australia) have barber’s pole worm resistant to this group. Few cases of resistance of liver fluke to closantel have been reported.

Macrocyclic lactone (ML)

Generally moxidectin is more potent than abamectin, which in turn is more potent than ivermectin. Moxidectin also has persistent activity. Resistance of black scour worm to this group has been reported in Australia, but confirmed cases are still uncommon and likely to exist on few properties. However, some properties in Australia have resistant small brown stomach worm. Resistance by barber’s pole worm to this group occurs on many properties in summer rainfall regions and on some properties in other regions. There is no reliable information on the resistance status of nodule worm. Unless resistance is severe, MLs may still be useful when administered with unrelated actives in combination products. Moxidectin-based long-acting products may still be useful when given with an effective primer (see notes in Drench Decision Guide on the use of long-acting products).

Amino-acetonitrile derivative (AAD)

Resistance to this group is still unknown in Australia. So far, there is no claim for nodule worm control.

Triclabendazole (BZ Flukicide)

Resistance of liver fluke to triclabendazole is emerging, but it appears that few properties in Australia have resistance to this active.

Isoquinolone (ISO)

Reports of resistance of Moniezia tapeworms are still uncommon.

Benzimidazole and levamisole (BZ and LEV)

Many properties in Australia have scour worms resistant to these combinations. Resistance by barber’s pole worm is largely restricted to summer rainfall regions where it is likely to occur on some properties. There is no reliable information on the resistance status of nodule worm. Unless resistance is severe, these combinations may still be useful when administered with unrelated actives in triple or quadruple combination products. Activity of the BZ group also aids in control of adult liver fluke. Resistance by liver fluke is likely to occur on very few properties in Australia.

Benzimidazole and salicylanilide (BZ and SAL-P)

This is a combination product for barber’s pole worm. Only the BZ ingredient has activity against susceptible scour worms. However many properties in Australia have scour worms resistant to this mixture. Resistance by barber’s pole worm is mostly restricted to summer rainfall regions where it is likely to occur on many properties (see benzimidazole and salicylanilides for resistance notes). There is no reliable information on the resistance status of nodule worm or liver fluke to this mixture/combination.

Benzimidazole and triclabendazole (BZ and BZ Flukicide)

Resistance by liver fluke to this combination is unknown. Many properties in Australia have scour worms resistant to this mixture. Resistance by barber’s pole worm mostly occurs in summer rainfall regions where it is found on many properties (see benzimidazole and triclabendazole for resistance notes). There is no reliable information on the resistance status of nodule worm.

Macrocyclic lactone and salicylanilide (ML and SAL-P)

This is a combination product for barber’s pole worm. Only the ML active has activity against scour worms. Few properties in Australia have black scour worms resistant to this mixture. However some properties have resistant small brown stomach worm. Resistance by barber’s pole worm occurs mostly in summer rainfall regions where it is found on many properties (see macrocyclic lactone and salicylanilides for resistance notes). There is no reliable information on the resistance status of nodule worm.

Macrocyclic lactone and triclabendazole (ML and BZ Flukicide)

This is a combination product for liver fluke and roundworms. Only the ML has activity against roundworms. Resistance of liver fluke to triclabendazole is emerging, but seems to be restricted to few properties. Resistance of black scour worm to this group has been reported, but confirmed cases are still few. However, some properties in Australia have resistant small brown stomach worm. Resistance by barber’s pole worm to this group occurs on many properties in summer rainfall regions and some properties in other regions of Australia (see triclabendazole and macro cyclic lactone for resistance notes). There is no reliable information on the resistance status of nodule worm.

Macrocyclic lactone and isoquinolone (ML and ISO)

See isoquinolone and macrocyclic lactone for resistance notes.

Benzimidazole and macrocyclic lactone and levamisole (BZ and ML and LEV)

Few to some properties in Australia have small brown stomach worm resistant to these combinations. Resistance of black scour worm to this group has been reported, but confirmed cases are still few. Resistance by barber’s pole worm is mostly restricted to summer rainfall regions where it is likely to occur on few to some properties. There is no reliable information on the resistance status of nodule worm. Resistance of liver fluke (to the BZ) is likely to occur on very few properties in Australia.

Benzimidazole and organophosphate and (BZ and OP)

Few properties have adult barber’s pole worm resistant to this combination. Because OPs have variable activity against scour worms and immature barber’s pole worm, the efficacy of this combination against these worms also depends on the resistance status of benzimidazole (see benzimidazole for resistance note). There is no reliable information on the resistance status of nodule worm.

Benzimidazole and levamisole and organophosphate (BZ and LEV and OP)

Few properties in Australia have adult barber’s pole worm resistant to this combination. Because OPs have variable activity against scour worms and immature barber’s pole worm the efficacy of this combination also depends on the resistance status of benzimidazole and levamisole (see benzimidazole and levamisole for resistance note). There is no reliable information on the resistance status of nodule worm.

Macrocyclic lactone and benzimidazole and and salicylanilide and levamisole (ML and BZ and SAL-P and LEV)

Few to some properties in Australia have small brown stomach worm resistant to this combination. Resistance of black scour worm to this group has been reported, but confirmed cases are still few. Resistance by barber’s pole worm is restricted to summer rainfall regions where it is likely to occur on few properties. In this product, the salicylanilide active is a short-acting form of closantel. There is no reliable information on the resistance status of nodule worm.

Macrocyclic lactone and benzimidazole (ML and BZ)

Some properties in Australia have small brown stomach worm resistant to this combination. Resistance of black scour worm to this combination has been reported, but confirmed cases are still few. Resistance by barber’s pole worm is likely to occur on many properties in summer rainfall regions and on some properties in other regions. There is no reliable information on the resistance status of nodule worm. Resistance of liver fluke (to the BZ) is likely to occur on very few properties in Australia.

Levamisole and isoquinolone (LEV and ISO)

Many properties in Australia will have scour worms resistant to the levamisole in this mixture. Resistance by barber’s pole worm is largely restricted to summer rainfall regions where it is likely to occur on some properties. There is no reliable information on the resistance status of nodule worm. Reports of resistance of Moniezia tapeworms to the isoquinolone in this mixture are still uncommon.

Levamisole and salicylanilide (LEV and SAL-P)

Many properties in Australia will have scour worms resistant to the levamisole in this mixture. Resistance by barber’s pole worm to this combination is largely restricted to summer rainfall regions where it is likely to occur on many properties (but generally few properties in other regions of Australia). There is no reliable information on the resistance status of nodule worm to the levamisole in this mixture.

Macrocyclic lactone and spiroindole (ML and SPIRO)

This combination is not available in drenches in Australia (Nov 2012). Resistance of small brown stomach worm, barber’s pole worm or black scour worm to this combination is not expected on release.

Benzimidazole and levamisole and isoquinolone (BZ and LEV and ISO)

Many properties in Australia have scour worms resistant to this combination. Resistance by barber’s pole worm is largely restricted to summer rainfall regions where it is likely to occur on some properties. There is no reliable information on the resistance status of nodule worm. Activity of the BZ group also aids in control of adult liver fluke. Resistance by liver fluke is likely to occur on very few properties in Australia. Reports of resistance of Moniezia tapeworms to the isoquinolone in this mixture are still uncommon.

Spiroindole (SPIRO)

This is not expected to be available as a single active ingredient drench.