Question: I suspect that the dip I use is no longer effective against ticks. Is this possible?
By Drs Arthur Spickett, Tom Strydom and Faffa Malan
Answer:
Controlling blue ticks is becoming more and more difficult in many areas in South Africa. It seems, at times, as if acaricides are no longer active. This is responsible for great economic losses to cattle farmers.
Apart from the direct cost of dip, there are also livestock deaths from diseases such as redwater (babesiosis) and gall sickness (anaplasmosis), which are transmitted by ticks.
Consequently, ticks cost the farmer a lot of money and livestock losses make a big dent in his profits. Africa’s bill for controlling ticks is probably greater than that of all other continents put together. As recently as 2006, South African farmers spent more than R250 million on controlling ticks.
Added to this are the costs and losses resulting from tick resistance. Resistance means, essentially, that there are individuals in any parasite population that are genetically resistant to a specific remedy or active ingredient even before the remedy is used for the first time to control those specific parasites. The majority, in such a population, are, in fact, initially killed by the ingredient. Put differently, the target species (ticks) can withstand the effect of the chemical remedy (acaricide) and to survive.
Although resistance has risen sharply, especially during the last decade, it is nothing new. The first published report on ticks resistance appeared in 1941, after the blue tick’s resistance to arsenic was discovered.
Two blue tick species occur in Southern Africa – the African blue tick (Rhipicephalus (Boophilus) decoloratus). which is the host of African redwater, and the Asiatic blue tick (Rhipicephalus (Boophilus) microplus), host of Asiatic and African redwater.
Their life cycles and treatment are virtually identical.
The blue tick occurs mainly on cattle. Its life cycle is as follows: An animal is parasitised by tick larvae, which occur on the grazing. The larvae feed (suck blood) for about seven days on the animal. They then moult, harden and develop into adults.
The adult female ticks start to feed, and when engorged, after about seven days, they fall off the animal and start to lay eggs within a week. The male ticks remain for a while on the animal and wait for the next adult female with which they mate.
Usually, it is only the engorged adult females that are visible to the farmer. The eggs hatch after about three weeks and the larvae wait for the next host to come along. It takes about three weeks from the time a larva gets onto the animal until she is an engorged female.
Factors that contribute to blue tick resistance are repeated use of the same active ingredient in the dipping fluid year after year to control ticks, short dip intervals, the relatively short life cycle of the blue tick (which means that more than one generation occurs during the year), ideal environment conditions and farmers’ misuse of dipping materials.
When the same remedy or active ingredient is constantly used, all the individual ticks that are susceptible to the remedy are eradicated, but the number of ticks that are resistant continues to grow exponentially. Consequently, it is possible that the entire blue tick population on the farm can become completely resistant to the active ingredient in the remedy.
Short dip intervals cause the susceptible ticks to be eradicated more quickly and the number of resistant ticks to grow more rapidly than the susceptible ticks.
The resistance of parasites is passed on to their progeny. The shorter the life cycle of the parasite, the more generations will occur throughout the year and the quicker the resistant individuals in a population will increase, in relation to the susceptible individuals.
The relatively short life cycle of the blue tick compared of the life cycle of two- and three-host ticks (of which, at most, a single generation occurs per year) explains why blue tick develop resistance to remedies more quickly.
The ideal environmental conditions for ticks to survive and increase would be about 27 degrees Celsius and 80% relative humidity. In such hot, humid conditions, ticks procreate optimally and numbers increase rapidly. If such conditions persist throughout the year, there will be more generations of ticks. This is why tick resistance is a greater problem in the warmer and temperate areas than in the drier, colder areas.
If ticks are exposed to lower concentrations of dips (whether plunge dip or spray dip) over a period of time, or if pour-on is not applied according to the correct dosage, ticks will develop a resistance to the remedy or to its active ingredient. The misuse of remedies, pour-ons in particular, contributes to the development of tick resistance.
Many farmers “formulate” their own pour-ons. Apart from a fact that doing so is illegal, ticks are exposed to lower concentrations of active ingredient, which leads to resistance. In addition, it cannot be said with any degree of certainty that the active ingredients will not be absorbed into the animal’s tissues and thus pose a threat to humans who consume the animal’s meat and other tissues.
If the farmer sees female ticks on his animals within one day after they have been dipped, it could indicate resistance. The Malelane experimental farm also tests ticks collected on farms, for resistance.
Unfortunately, there is no quick fix for resistance.
Also read: Ticks in South Africa are becoming resistant to pesticides – and may become uncontrollable
The most commonly used method for controlling ticks remains chemical control. Only three groups of active ingredients are available for conventional tick control, namely organophosphates, pyrethroids and formamidines (amidines for short). They are used in plunge and spray dips and also pour-ons.
If a farmer does not achieve the desired result with one of the groups, he should switch to another.
It makes no sense to switch from one remedy that has, for example, pyrethroid as an active ingredient to another containing the same active ingredient.
If there is multiple tick resistance, to two or three groups, the situation becomes more complex. Then the farmer will have to use alternative control measures, such as systematic remedies. These groups are macrocyclic lactones (remedies that contain ivermectin, doramectin and moxidectin) and the tick growth inhibitor, fluazuron.
The farmer should consult an expert, as incorrect use could have catastrophic results.
The conclusion is that cattle farmers, and consequently the pharmaceutical industry as well, should pay particular attention to the most cost-effective method for controlling ticks. Nobody can afford the luxury of inefficient tick killers, least of all the farmer who has to produce food.
The big companies will no doubt continue their search for new chemical groups that can control ticks, and for effective, labour-saving application techniques.
The farmer cannot, however, allow the cost of chemical control to exceed production profit. For this reason, integrated control of ticks is essential, in other words, the control of ticks to keep damage at economically acceptable levels. This requires a combination of host resistance, inoculation and the control of animal pregnancy, along with strategic and/or opportunistic chemical treatment to reduce the effect of ticks, but definitely not intensive control.
Oxpeckers and certain types of fowl can also play a role in helping to fight ticks biologically. In such cases, acaricides such as pyrethroid, amidine and fluazuron, which are not detrimental to oxpeckers, should be used.
How To Prevent Resistance
The farmer’s most important goal in his programme to control ticks has to be to prevent resistance. Here are four useful hints:
- Use a remedy only for as long as it is effective. When resistance appears, switch to another group. The farmer can return to the first group again later, as the ticks will have, in the meantime, lost their resistance to that group. Alternating between the various groups is not recommended, because the ticks will develop resistance to more than one active ingredient.
- Dip less frequently when ticks are inactive, such as in winter, because short intervals between dips contribute to the development of resistance.
- Use registered dip remedies strictly according to the instructions. Make sure that the correct dose of a pour-on is used, and that the dip concentration in plunge or spray is correct. Do not use homemade mixtures.
- Avoid the inadvertent purchasing of “stud” ticks. Blue tick resistance is common, and many farmers have fallen into the trap of buying, at auctions or directly from farmers, animals that come from farms where there is resistance to one or more active ingredients. If these animals are immediately sent out to the veld, resistant ticks will land in the veld (and on his cattle).
