Ticks are bloodsucking parasites of domestic and wild animals. They are not insects but belong to the group called Acarina, together with scab and mange mites.
They are obligate parasites, i.e. they can neither survive nor complete their life cycle without parasitizing their hosts.
Among the external parasites of horses and other equids, ticks belong to the most harmful ones because they can transmit numerous microbial diseases.
Ticks occur worldwide, but the species prevailing in each region are different. As a general rule, ticks are substantially more abundant in tropical and subtropical regions than in regions with a cold to moderate climate. And tick species found in tropical and subtropical countries are mostly different from those that are common in countries with a cold winter (e.g. Canada, Northern USA, Europe, etc.).
In tropical and subtropical regions ticks are more frequent in rural zones with abundant livestock than in dense forests, and are active year round. In regions with a cold winter, ticks are more abundant in and around forests than in pastureland, and are active only from late spring to early autumn.
Horses and other equids are important hosts for ticks, and almost all tick species that infect livestock can infect horses as well.
Before taking their blood meals, ticks that infest pets are rather small: larvae are smaller than 1 mm, nymphs are 1-2 mm long, and adults are 3-5 mm long, depending on the species. But engorged adult females of certain species can be up 2 cm long (like a large bean or a hazelnut) and more, 50 to 100 times larger in volume than unfed.
Click here to learn more about the general biology of ticks.
Which tick species are important for horses?
Most hard tick species can infect horses and other equids. The belong to the following genera (for more specific information click the corresponding links):
- Amblyomma: mainly in America and Africa. Species-specific distribution. Amblyomma americanum and Amblyomma cajennense in America; Amblyomma hebraeum in Africa, Amblyomma variegatum in Africa and a few Caribbean islands.
- Boophilus (nowadays included in the genus Rhipicephalus): In most tropical and subtropical regions of the world.
- Dermacentor: worldwide. Species-specific distribution. Dermacentor nitens (= Anocentor nitens), the tropical horse tick is particularly important for horses in tropical America.
- Haemaphysalis: worldwide, excepting the Americas. Species-specific distribution.
- Hyalomma: mainly in Europe and Asia. Species-specific distribution.
- Ixodes: worldwide. Species-specific distribution. In Australia Ixodes holocyclus, the paralysis tick of Australia, the scrub tick, is important for horses.
- Rhipicephalus: worldwide. Species-specific distribution. Rhipicephalus sanguineus worldwide. Rhipicephalus appendiculatus and Rhipicephalus evertsi in Africa.
Among the soft ticks, Otobius megnini, which is often found in the ears of horses, can be a local problem in Latin America and Africa.
The significance of ticks for horses is completely different for stock horses than for pet or sport horses. Whereas in most of Europe and North America pet or sport horses may get a few ticks during a ride, stock horses, particularly those for working with cattle in tropical and subtropical regions may pick hundreds if not thousands of ticks. Obviously, both the harm caused by ticks to horses as well as the methods for their control are not the same for stock horses in the tropics than for pet of sport horses in Europe and North America.
For a sport horse owner that finds ticks on its horse it is not very important to know the particular species. However, knowing the species is important for the veterinary doctor, because not all tick species transmit all tick-borne diseases. Therefore, if possible, the concerned tick(s) should be picked off (see below) and brought to the veterinary clinic to be determined. If a horse has got many ticks, most of them are likely to be of the same species.
With very few exceptions all species that affect horses affect livestock, pets, wildlife and humans as well.
Where do ticks live and how can a horses get infested with ticks?
The vast majority of ticks species live outdoors, especially in places used by livestock (cattle, sheep, goats) and/or wildlife for grazing and resting, whereby small mammals (e.g. rodents, rabbits, hedgehogs, etc.) and birds are often important hosts as well, especially of immature tick stages (i.e. larvae and nymphs) that can also infest pets and humans. In regions with moderate or cold climate (Europe, North America) ticks are rather found in forests and woods or close to them. They can also be abundant in peri-urban parks, recreational and residential areas, especially if they are also visited by wildlife. Ticks are usually not present in cropland, but can be found on its borders.
Therefore it is unlikely that a horse (or its owner) gets ticks while kept indoors. However, if a horse gets ticks, brings them home and engorged adult females drop to the ground somewhere in or around the stable, such females will lay eggs by the thousands. And microscopic larvae that hatch out of the eggs can indeed re-infest horses, pets or humans.
Ticks (either larvae, nymphs or adults) do not actively search for a host, but instinctively climb to the tip of grasses or on leaves of shrubs and bushes in the vegetation, where they wait for a suitable host to pass by. This behavior is called questing. When a suitable host passes by and touches the grass or the leaves, the questing ticks just hang on to it. They recognize a suitable host by its body heat and exhaled CO2 (carbon dioxide), which they can perceive with sensory organs, e.g. the so-called Haller's organ in their legs.
After getting onto a host, hard ticks (either larvae, nymphs or adults) will crawl around in its hair coat for 1 to 2 hours searching a good place to bite (which can be species-specific, e.g. the ears). Once they feel comfortable they will attach and start their blood meal, which can last for days. After the blood meal they drop to the ground for molting or egg laying. It is extremely unlikely that an undisturbed tick that has found a suitable host abandons it without attaching and feeding.
After dropping they do not move away. Larvae and nymphs molt to the next stage in a few days and start again questing. Engorged females deposit their eggs during several days and die. Larvae that hatch out of the eggs immediately start questing without moving away.
As a consequence of this behavior, the highest number of infesting ticks will be found in and around those places that are most visited by livestock (especially cattle) and/or wildlife: water and feeding points, preferred resting places (e.g. below large trees in the pastures), etc. In tick endemic areas, especially in tropical and subtropical regions, if a horse walks through such a place, it may pick dozens if not hundreds of ticks.
This behavior means that hard ticks neither jump onto their preys, nor drop down from the trees. Australian Ixodes holocyclus seems to be an exception: it does climb trees and falls down onto people or animals staying underneath. As a general rule, hard ticks are not transmitted from one animal to another one, neither within a herd, nor from cattle to horses, nor form horses to humans, etc.
This is different for soft ticks. Their blood meals are shorter and they leave the host repeatedly, to come back again. Between the meals they remain in their nests, which they leave for a new meal on whatever host they can attach to. The good news is that soft ticks are significantly less abundant than hard ticks in most regions of the world.
What harm can cause ticks to horses?
Tick bites are usually not painful for horses and other hosts. The reason is that ticks introduce natural painkillers with their saliva to increase the chance for remaining unnoticed by the host during the daylong blood meal. However, if a horse gets dozens or even hundreds of ticks, it may well be significantly annoyed by the ticks themselves, regardless of whether it becomes infected with a tick-borne disease or not.
Blood loss due to a few ticks is irrelevant for a horse's health. Most pet and sport horses in Europe or North America will usually catch only a few ticks outside. But if a stock horse gets bitten by hundreds of ticks, blood loss can certainly lead to anemia.
In many tropical and sub-tropical regions, the small injuries caused by tick bites can attract parasitic flies that lay their eggs on this wounds (e.g. screwworm flies) and develop into cutaneous myiases. Larvae that hatch out of the eggs feed on the horse's tissues and cause severe injuries. If left untreated fatalities are possible within a few days.
Poisoning (toxicosis) is another possible harm caused by tick bites. Ticks do no inject a strong toxin as snakes, spiders or scorpions. But the tick's saliva contains a complex mix of several substances that strongly affect the host's immune system. For several tick species this can lead to a general toxemia (= poisoning) of the host. Such toxemia can lead to paralysis of the host that can be fatal. Ixodes holocyclus in Australia can cause tick paralysis of horses, humans, dogs, cattle, and other animals; two or even a single tick seem to be enough for causing a serious problem. Fatalities among infected horses are frequent.
A major threat for horses bitten by ticks is transmission of tick-borne diseases. Almost all tick species transmit one or more tick-borne diseases, e.g. babesiosis, borreliosis, theileriosis, etc. But not all species transmit all the diseases. Which tick species transmit which disease is regionally different. Most veterinary doctors know which tick-borne diseases a particular tick species may transmit in a given region. In endemic regions, stock horses regularly exposed to ticks usually develop acquired immunity. Pet and sport horses may develop it as well, but only if they are regularly exposed to tick bites.
Humans may be affected by some of these tick-borne diseases as well, but only if they are also bitten by ticks, not because the disease that affects the horse is contagious for humans. As previously mentioned, it is also extremely unlikely that a tick that has bitten a horse will afterwards bite its rider and transmit the same disease.
The clinical symptoms of tick-borne disease are frequently unspecific and early diagnosis is not always easy. Unfortunately it is not rare that diagnosis is done too late. In the following the most relevant aspects of tick-borne diseases that affect horses are summarized.
- Theileriosis, (also called piroplasmosis) caused by Theileria equi (formerly known as Babesia equi), a unicellular microorganisms (protozoan) the develops in the blood and attack the blood cells. They are microscopic (about 2 mcm in length). It is common in tropical regions in most continents. It causes high fever, anemia and hemoglobinuria (low hemoglobin) together with depression, lack of appetite, small (petechial) hemorrhages, and jaundice of the ocular mucous membranes. An acute outbreak can kill a horse within a few days. Several tick species of the genera Rhipicephalus, Dermacentor and Hyalomma have been reported to transmit Theileria equi. Unfortunately, many of these symptoms are not specific for this disease but are similar to other diseases (e.g. Equine Infectious Anemia, trypanosomiasis, etc.). Diagnosis requires specific microscopic and/or serological tests. Affected horses that survive the infection acquire immunity that lasts for about one year. Particular care is a must for horses coming from a Theileria-free area that are brought into an endemic area, because they have no acquired immunity and are at high risk of suffering an acute severe infection.
- Piroplasmosis (also called babesiosis) caused by Babesia caballi, common in Europe, America and Asia. It is closely related to Theileria equi but less pathogenic. Clinical signs show a large variation. It can cause anemia and jaundice, but hemoglubinuria (low hemoglobin) is unusual. Lack or coordination and restlessness may occur as well. Paralysis due to harm to the central nervous system is common. Walking in circles may also happen. Fatalities are possible. Diagnosis requires specific microscopic and/or serological tests.
- Borreliosis (also called spirochaetosis) caused by Borrelia theileri (spirochaetosis), a bacterial micro-organism that affects also cattle, sheep and goats. In East Africa it is transmitted by ticks of the species Boophilus decoloratus and Rhipicephalus appendiculatus. They can cause weight loss, weakness and anemia. Fever attacks are often intermittent. As a general rule, borreliosis in horses is moderately benign.
- Lyme disease caused mainly by Borrelia burgdorferi. This disease affects also humans, dogs and other mammals. It is transmitted mainly by ticks of the genus Ixodes that are common worldwide, also in regions with moderate climate in Europe and America. Clinical signs are quite variable and may include fever, anemia, swelling of the joints, edema, lameness and even encephalitis. As for many other tick-borne diseases these symptoms are not specific and may be confused with other diseases. Diagnosis requires also specific microscopic and/or serological tests.
- Anaplasmosis (also called ehrlichiosis, tick-borne fever, pasture fever) caused by Anaplasma phagocytophilum (formerly known as Ehrlichia phagocytophilum, Ehrlichia equi). It is a ricketssial parasite. In Europe it is transmitted by Ixodes ricinus, in North America mainly by Ixodes scapularis andIxodes pacificus. It affects horses, but also humans, dogs, cattle and other mammals. These bacteria live inside certain blood cells (granulocytes) and in humans the disease is called human granulocytic anaplasmosis. In horses and other animals it can cause anemia, lameness, lethargy, ataxia (uncoordinated movements), lack of appetite and pain in the limbs. As for many other tick-borne diseases these symptoms are not specific and may be caused by other infections as well. Diagnosis requires also specific microscopic and/or serological tests.
A single tick can transmit the disease! But it is important to know that this does not always happen. Successful transmission of the disease occurs several hours after the tick has started biting, depending on the tick species and the disease. The longer the bite, the higher the risk of disease transmission. This is why it is advisable to find the ticks and to remove them as early as possible, particularly for sport and pet horses that are usually not exposed to ticks. Therefore, after a horse has been outdoors in a risky environment it should be thoroughly inspected, if possible not later than 12 hours after the walk. It is not recommended to inspect the horse immediately after the walk because most unfed ticks are rather small and difficult to notice. About 12 hours later they have started to engorge and are easier to find.
For any potential host, whether a horse, a pet or their owners, the risk of becoming infected with a tick-borne disease depends strongly on the region and the season. The number of active ticks in a region varies along the season (winter versus summer, or humid versus dry). And not all ticks are infected with microbial pathogens. The infection rate of ticks varies considerably from one region to another one. By an infection rate of 10% only 1 in 10 ticks are infected with pathogens. But the pathogens can be more or less virulent in certain tick populations than in other ones. If the pathogen is only mildly virulent, many bitten and infected hosts will not develop the disease because it is neutralized by the host's immune system. All this can result in a risk of <1% of developing the disease if bitten. But if the pathogen is highly virulent, most infected animals will develop the disease. This can result in chances of developing a disease of >10%. Unfortunately, it is impossible for a horse owner to estimate these risks. Therefore it is highly recommended to check and follow whatever local warnings and recommendations regarding tick-borne diseases.
For a sport or pet horse owner it is important to be aware and on the alert, particularly in regions at risk. If ticks are found on the horse it is advisable to remove them (see later), preserve a few ones (e.g. in alcohol) and bring them to a veterinary doctor for determining the species. Knowing the tick species indicates which diseases may have been transmitted. Afterwards the horse has to be carefully observed for whatever abnormal behavior: fever, lack of appetite, abnormal movements, etc.
However, most of this is not practicable for stock horses in tropical or subtropical regions, simply because horses may become infested with dozens or even hundreds of ticks, and this not only once, but regularly during the tick season. The good news for these stock horses is that most of them have acquired immunity to the diseases transmitted by ticks.
It is good to know that when inspecting a horse for ticks, what most pet owners will find are more or less engorged adult ticks, which can be between 0.5 and 2 cm long, something between a rice grain and a large bean. Unfed adults reach 0.2 to 1 cm, depending on the species. Engorged larvae are usually 1 to 2 mm, too small to be detected by the naked eye. Engorged nymphs reach 2 to 5 mm, small enough to remain unnoticed by most horse owners. Unfortunately larvae and nymphs are also capable of transmitting diseases. However, larvae and nymphs of many species prefer smaller hosts (rodents, birds, rabbits, etc.) and are less likely to infest horses.
There are so far no vaccines to protect horses against most tick-borne diseases and the best prevention is to avoid visiting tick territory during the tick season, or to thoroughly inspect the horses after such a visit. Horses and other animals becoming infected with tick-borne diseases can be treated with specific antibiotics and other supportive medications. But it is crucial that the disease is correctly diagnosed as fast as possible after infection.
Finding ticks on horses and removing them
Once a tick has found a host, it does not bite and attach immediately but will crawl around the hair coat searching a adequate place to bite, e.g. where the skin is softer, or warmer, etc. They crawl around for up to several hours until they find a suitable place. Many tick species have preferential sites for biting: in or around the face, between the legs, in the ears, on the neck, below the tail, in skin folds, etc. This means that when a horse has got ticks during a walk outdoors and comes home, some ticks may still be crawling around, while other ticks have already attached and started their blood meal.
It is important to know that usually tick bites are not itchy or painful, i.e. if the horse does not scratch or lick itself, it does not mean that it is free of ticks. If they scratch intensively, they are more likely to have fleas, mites or lice.
How to inspect a horse for ticks
To inspect a horse for already attached ticks you have to open the hair coat and patiently look for ticks and/or thoroughly feel the body surface for any lumps under the hair, better against the nap. Pay close attention to the ears, around the face and the eyes, on the legs, between the toes, etc. However, most likely you will not find those ticks that have attached shortly before, but only those that have already engorged a little bit, i.e. that have been sucking blood for a few hours.
Unattached ticks are much more difficult to find because they are unengorged and thus much smaller than attached ticks.
If you find 2 to 3 attached ticks, you can try removing them by hand. If you find dozens of ticks, it's better to treat the horse with a tickicide, because the more ticks you find on your pet, the more ticks you will miss that will remain attached.
Removing the ticks one by one
There are conflicting opinions regarding the easiest and safest way of removing ticks from animals (or humans). Some people recommend to spread oil, butter, petrol, alcohol, nail polish, turpentine, etc. over the tick and wait until it detaches. Others may even approach a burning cigarette to the ticks to frighten them off. The risk of this approach is that the tick may remain attached too long before detaching, or it can be irritated and inject more saliva, or it may die but remain attached.
Others recommend to spread nothing over the tick, but to grasp it directly (perhaps with thin gloves if your are or could be allergic to ticks) as close to the mouthparts (i.e. to the horse's skin) as possible. Then pull very firmly, because the tick mouthparts are often very strongly anchored in the skin. You may use a specific tool such as tick tweezers, scoops, hooks, loops, etc. One risk of this operation is that while firmly grasping the tick, part of its gut content may be injected into the horse. To avoid it pull firmly but gently and straight, without twisting or squeezing the tick. Another risk is that the tick "head" breaks, the mouthparts remain embedded in the skin, and the injury becomes infected. In most cases this is not a problem: the mouthparts will be eventually sloughed like a splinter. After removal the attachment site should be disinfected.
Removed ticks should be brought to a veterinarian for determining the species, either preserved (and killed) in an organic solvent (e.g. alcohol) or in an airtight container. Remember that engorged adult females, if alive, will start laying thousands of eggs a few days later. If you dump living ticks in the backyard or in the stable, these eggs will produce thousands of infective larvae!
There is very little risk of direct harm to the person that removes the ticks, unless he/she is allergic to ticks, which can happen after repeated contact with them. This is why using gloves is advisable, especially for nurses or veterinarians that come often in contact with ticks in endemic regions. Otherwise attached ticks that are removed won't bite back or be otherwise poisonous or contagious.
Non-chemical prevention and control of ticks on horses
Best prevention is to keep away from tick territory during the tick season (late spring and summer in most of Europe and North America). During the tick season, best prevention is to restrict the ride to roads, ways, or paths uncovered by vegetation. Ticks wait for a host mostly on grass, shrubs or bushes, not on a road where they would quickly die when exposed to the sun. Places frequently visited by wildlife or other livestock that can also carry ticks should be avoided.
Tick vaccines for horses?
For the time being there are no vaccines against ticks that affect horses. There are a few tick vaccines against cattle ticks, but they are useless against other tick species. And it is unlikely that this changes in the near future.
Click here to learn more about vaccines against ticks and other veterinary parasites.
Natural tick repellents for horses?
Repellents do not kill the parasites but keep them away from their hosts. Most commercial repellents against insects and/or ticks are for human use. Besides those repellents based on synthetic chemicals (e.g. DEET) with repellent effect, other contain so-called natural products (e.g. pyrethrins, essential oils, plant extracts, etc.). There are such products for horses too. But the repellent effect of most of these products is against mosquitoes and a few fly species. The repellent effect against ticks is much weaker, it will last only a few hours if at all.
Some chemical parasiticides that kill ticks have also a certain repelling effect, e.g. synthetic pyrethroids (cypermethrin, deltamethrin, permethrin). However, the repellent effect is usually insufficient to protect horses against ticks.
Click here to learn more about repellents.
Biological control of ticks?
Biological control means controlling parasites using their natural enemies. There are no biological methods to kill ticks on a horse other than picking them off by hand, if you consider humans as natural enemies of ticks.
In some countries entomopathogenic fungi have been tried for controlling ticks in parks and recreational areas highly infested with ticks because they are visited by wildlife (deer, foxes, rodents, etc.). Practical results have been rather modest so far.
Learn more about biological control of ticks and mites.
Homemade traditional remedies against ticks on horses
There are numerous homemade remedies against ticks, most of them based on traditional recipes using locally available herbs or other natural products. They are the result of centuries of efforts for finding relief against ticks when modern tickicides were not available.
The bottom line is that no such remedies are as effective as modern synthetic pesticides. They may bring partial relief for a few hours, maybe a few days, but certainly not week or month-long protection. Such products are usually substantially less effective against ticks than synthetic tickicides. Besides being less effective, many of them have a very short residual effect, i.e., they protect no more than a few hours to a few days against re-infestation. The reason is that they are easily washed away by water (rain, washing, swimming, etc.) or are broken down by sunlight, or they simply evaporate very quickly.
There are numerous Internet sites with a lot of homemade remedies and recommendations, but almost none of them are supported by reliable investigations. Nevertheless, it may be worth trying them: usually they are not expensive and the risk of serious side effects is usually not too high. Many such remedies are based on do-it-yourself recipes based on plant extracts or products (citronella oil, neem, rosemary, lavender, lemon balm, etc.). Try them. If they work, fine. If they don't, you will never know whether the recipe is useless or whether you did something wrong. But it doesn't matter: just try another one.
It is good to know that in most countries products containing such "natural parasiticides" (e.g. plant extracts) are submitted to much less stringent regulations than veterinary parasiticides. This means that they don't need to proof their efficacy against parasites, or their safety for the horses, users and the environment through such strict and thorough investigations as the products containing synthetic parasiticides. Many regulatory authorities seem to simply assume that being natural they are "safe enough", or at least not harmful, and that users will find out themselves whether they are effective or not... Obviously, the cost and the know-how to develop and market such "natural products" are substantially lower than for veterinary medicines containing synthetic parasiticides. This low cost explains their proliferation. It is not possible to deal with such products here in detail.
BUT: when dealing with plant remedies, especially self-made ones, it is good to know that the active components in herbs are also chemicals, i.e. specific molecules that have a biological effect, in this case a tick killing or repelling effect. They have been naturally synthesized in the plants. But this says nothing about the safety of such chemicals. It is wrong and dangerous to believe that something is safe because it is natural! The most potent poisons known are often natural, i.e. of plant or animal origin. And by the way, many such "natural chemicals" are also manufactured industrially and used in numberless so-called "natural" or "biological" products".
Click here if you are interested in medicinal plants for controlling ticks and other external parasites of livestock, horses and pets.
There are two completely different situations regarding tick control on horses.
- Pet and sport horses that occasionally visit tick territory during a ride
- Stock horses that work in tick territory, mainly in cattle farms.
Most pet and sport horses may catch "a few ticks" during a ride. Tick "control" usually means either preventing this to happen (e.g. avoiding tick territory) and/or killing or removing those few ticks caught by the horse after the ride. Several tickicides approved for use on horses (sprays, pour-ons) provide appropriate curative and preventative efficacy in these situations. Some "soft" products (shampoos, sprays, soaps, etc.) may provide sufficient control as well.
Stock horses in tropical and subtropical regions may catch dozens if not hundreds of ticks regularly. Some tickicides approved for use on horses (dips, sprays, pour-ons) are adequate for killing such ticks and/or for preventing the infestations. "Soft" products (shampoos, soaps, sprays, etc.) are often completely useless in such situations. In many tropical and subtropical regions, stock horses working in cattle farms are mostly treated (dipped, sprayed, etc.) with the same products as cattle, often even together with the cattle.
Nowadays, there are basically two types of veterinary products containing tickicides for horses, all for external use:
- Pour-ons, i.e. ready-to-use liquids that are poured along the backline and are applied about once a month. Most pour-ons for horses are also approved for use on cattle and other livestock and contain synthetic pyrethroids (e.g. cypermethrin, deltamethrin, permethrin, etc.).
- Concentrates for topical administration (dipping, spraying or dusting). Most concentrates are also approved for use on cattle and other livestock and contain organophosphates (e.g. coumaphos, chlorfenvinphos, etc.), synthetic pyrethroids (e.g. cypermethrin, deltamethrin, permethrin, etc.), or mixtures of noth chemical classes.
Modern very effective tickicides for use on cattle contain mainly macrocyclic lactones (e.g. doramectin, ivermectin, eprinomectin, moxidectin) and tick development inhibitor (mainly fluazuron) and are administered either as pour-ons or as injectables. Almost none of these products is approved for use on horses. Macrocyclic lactones approved for use on horses (mainly ivermectin and moxidectin) are all for oral administration and have no claim for tick control.
The main reason for the lack of modern effective tickicides for use on horses is that the horse market is smaller than the pet or the livestock market and thus not attractive enough for most Animal Health companies to invest in such products for use horses.
WARNING. NEVER USE amitraz products ON HORSES because amitraz is toxic to horses. Such products containing amitraz are often used in many countries for tick control on cattle, other livestock and dogs.
|If available, follow more specific national or regional recommendations or regulations for tick control on horses.|
Several tick species have developed resistance to tickicides. Widespread resistance to most chemical classes (organophosphates, synthetic pyrethroids, amitraz, macrocyclic lactones, etc.) has been reported for Rhipicephalus (Boophilus) microplus in Latin America and Australia. A similar situation applies for Rhipicephalus (Boophilus) decoloratus in Southern Africa. There are a few reports on resistance of the brown dog tick, Rhipicephalus sanguineus to amitraz, organophosphates and synthetic pyrethroids, of Rhipicephalus evertsi and Rhipicephalus appendiculatus to organophosphates and synthetic pyrethroids and of Amblyomma cajennense to synthetic pyrethroids.
Summarizing it can be said for Europe, the USA and Canada, that if a particular product has not achieved the expected efficacy, it is most likely because the product is not adequate for tick control on horses or it was not used correctly, not because the ticks have become resistant. In Australia, Latin America and Southern Africa the risk that some ticks that infect horses are already resistant to tickicides is higher.