Article supplied by Afrivet.
Resistance entails the ability of a population (in this case, ticks) to survive a dose of acaricide that would normally prove lethal to a susceptible population of the same species. It results from genetic mutations that are then selected and passed on to future generations after regular exposure to a certain acaricide.
Because blue ticks, Ripicephalus (Boophilus) decoloratus and R. (B) microplus, are single-host ticks, they tend to be exposed to acaricides more frequently when dipping takes place regularly, and they are more likely to develop resistance to the acaricide product in use. Some tick populations are already showing resistance to all three classes of commercially available topical products.
Certain management practices encourage the development of resistance on a farm.
- Poor biosecurity. A population of resistant ticks can easily be introduced to the farm when buying animals. Quarantine new cattle and ensure the effective removal of all ticks before introducing them to the herd.
- Using the same product consistently for a long period of time. This puts pressure on the tick population to genetically select the resistance genes. The population of resistant ticks will not be effectively controlled.
- The use of high-concentration pour-ons. The resistance to pyrethroid acaricides is developing rapidly and may be as a result of the use of high concentration pour-ons.
- Using combination products. In some cases, the use of combination products can promote the development of resistance to both ingredients. However, there are certain products that, when used in combination, can have a synergistic effect and increase efficacy results.
What should one do?
Send a sample of dip wash to a laboratory to establish that the acaricide is being used correctly and that it is being mixed to the concentration recommended by the supplier. The lab can then make a recommendation for replenishment rates if necessary.
A sample of ticks can also be sent to a laboratory for resistance testing. The ticks will be tested against the three most commonly used active ingredients namely, amitraz, cypermethrin and chlorfenvinphos.
So now what?
If resistance to one or more acaricide has been established, the following can be done:
- If resistance to one or two products is present, change to a different (or the remaining) class of active ingredient immediately and monitor the efficacy closely.
- Use the new product meticulously and for as long as possible and continue to monitor the product strength and the tick population for resistance.
- The macrocyclic lactones (MLs), such as Ivermectin (eg Afrivet Ecomectin 1% G2275) and insect growth regulators (IGRs), like Fluazuron, are available for use in multi-resistant blue tick populations, but their use should be strategic and careful.
Biosecurity measures that ensure that resistant ticks are not introduced to the herd, are essential. New cattle should be quarantined and treated twice with two different products (preferably not the product used by the seller) before mixing the new cattle with the farm herd. Correct use of the acaricide and monitoring the strength of the mixed product is a good way to ensure that resistance is not encouraged through under or over-strength dipping.
Certain ticks prefer certain parts of the host’s body as sites of attachment. Careful hand-dressing of these areas with the acaricide solution will help tick control efforts and slow down the development of resistance. Blue ticks prefer the neck, shoulders, sides of the body and dewlap. Also remember that nature has provided effective tick control partners in the oxpecker birds. Use products that are oxpecker friendly.
Knowing the status of resistance of the tick populations on the farm is the first step in tackling this challenge. Afrivet Laboratory Services in Pietermaritzburg conducts resistance tests on ticks and also tests the strength of dip wash or spray race product samples.
For more information, phone Afrivet on 012 817 9060 or visit www.afrivet.co.za.