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Targeting tricky resistant ticks


Figure 1. Engorged adult female cattle tick (upper left) and adult male cattle tick (lower right). Image courtesy of Ralph Stutchbury.
Figure 1. Engorged adult female cattle tick (upper left) and adult male cattle tick (lower right). Image courtesy of Ralph Stutchbury.

Cattle ticks (Rhipicephalus australis) might be tiny, but these eight-legged parasites pack a punch, spreading tick fever – which can be fatal – as well as causing hide damage and slowing down growth rates of cattle.

Although chemicals are available to keep tick numbers under control, ticks adapt genetically and rapidly develop ways of living with our chemical treatments, so resistant cattle ticks are common across northern Australia. Here, NSW vet Matt Playford, Dawbuts Animal Health, gives an insight into ticks and how resistance can be diagnosed by submitting ticks to a laboratory.

 

History of resistance

Chemical-resistant cattle ticks were first identified in Queensland in 1937, 40 years after the introduction of arsenic dips.

Since then, organochlorines (DDT), organophosphates, carbamates, amidines (amitraz) and synthetic pyrethroids have all been used in dips and sprays, and fluazuron in a pour-on application. All these chemicals have developed some level of resistance, on average 10 years after the release of the chemical class. Overseas, resistance in cattle ticks has also been detected to fipronil and spinosad, chemicals that have not been registered for use against cattle ticks in Australia.

More concerning, cattle ticks in Central and South America have developed resistance to the mectins (macrocyclic lactones or MLs), a class of chemical used widely in Australia to control ticks and seen by many as ‘the last bastion’ in our chemical armoury.

 

Know your chemicals

Here’s a closer look at the different chemical groups for treating cattle ticks:

Chemical group

Application

Notes

Amitraz (amidine)

Dips and sprays, including spray races

Knockdown

Organophosphates (OPs)

Ear tags* , back-rubbers* , dips and sprays

Knockdown. Also effective against buffalo fly

Synthetic pyrethroids (SPs)

Ear tags* , dips and sprays (sometimes in combination with OPs)

Knockdown. Also effective against buffalo fly

                   

Macrocyclic lactones (MLs, mectins)

Pour-on, injectable or ear tags* (injectable gives prolonged period of tick control)

Knockdown. Also effective against buffalo fly, lice, mites and internal parasites.

Fluazuron (tick development inhibitor)

Pour-on

Preferably used in combination products (with ivermectin), or concurrently with another product for knockdown effect.

 

The silver lining for resistant ticks

Research has shown that if amitraz is not used for three years, populations of cattle ticks will lose their resistance and revert back to susceptibility. This is because amitraz-resistant ticks are less ‘fit’ and don’t survive or breed as well as susceptible (non-resistant) ticks.

 

Preventing resistant ticks

Decreasing the number of treatments is the most effective way to avoid selecting for resistant ticks. Each time a chemical is used for tick control, ticks can survive treatment and lay resistant eggs. As the number of resistant ticks increases, they make up a greater proportion of the tick population, until only resistant ticks remain.

However, this strategy leads to higher risk of tick fever and tickrelated production losses.

The solution? Vaccinate for tick fever and use a range of methods (integrated pest management) to keep tick numbers down below the economic threshold.

The right combination of methods is different for each property, and includes:

■ selecting appropriate cattle genetics

■ timing treatments to spring and summer to suppress build-up of tick numbers

■ spelling paddocks and controlling feral tick hosts to allow larval ticks to die out

■ rotating chemical groups and using combination products

■ ensure correct dose for pour-on or injectable products and complete coverage of chemical when dipping or spraying cattle (see product label for directions).

 

Testing for resistance

Ticks can be tested for resistance to the chemical groups listed above.

Queensland Biosecurity Sciences Laboratory carries out two different types of resistance tests (bio-assays) for cattle ticks:

■ Adult Tick Immersion Test (fluazuron test): this requires female ticks that are engorged but not yet laying eggs.

■ Larval Packet Test: this tests knockdown chemicals.

Results are generally available in seven to eight weeks. Producers across northern Australia are encouraged to contact their local Biosecurity Officer or private veterinarian prior to submitting samples.

 

What about the tick vaccine?

Many producers will remember TickguardTM, a vaccine which, when used every six to eight weeks, would reduce cattle tick numbers by half and reduce infestations on paddocks by up to 70%.

This product stopped being sold in Australia in 2002, but research continues (supported by MLA) to provide producers with a tick vaccine with higher efficacy and longer protection period that can make a real difference to sustainable tick control. 

 

Seasonal action plan

Test for resistant ticks by talking to your vet or Biosecurity Officer and submitting engorged ticks to the laboratory.

Use integrated pest management to avoid chemical-resistant ticks – this includes vaccination for tick fever, paddock management and genetic selection. Combinations of chemicals and rotating chemicals can be used if frequent treatments are conducted.

Access tools and guides to manage ticks at www.tickboss.com. au/cattle