From spring to fall, they wait, perched on tall grass, brush, or leaves. On the lookout for any animal (or human) passing within reach to cling to it and feed on its blood. Piroplasmosis, hemorrhagic fever are so many little “gifts” that they can carry in their luggage. When the time comes for them to sustain themselves on the backs of our companions (… or ours). Small point on the identity, the way of life. And the means of fight against this not very sympathetic host and definitively undesirable.
Ticks are blood-sucking parasites that regularly infest pastured horses. They are particularly common from spring to fall, but they can remain active in mild winters. If tick bites are not serious in themselves, the fact that they can transmit several diseases. Such as piroplasmosis, equine anaplasmosis or hemorrhagic fevers, is much more worrying. Each tick bite constitutes a significant risk of transmission. It is therefore essential to minimize any contact of ticks with our equines as much as possible.
Ticks are the largest representatives of the order of mites (3 to 6mm on average. Which can reach 2cm once engorged with blood). All are blood-sucking parasites. To date, there are nearly 900 species listed throughout the world.
Some are exclusively dependent on a given host species (we then speak of a monotropic species. Such as the dog tick, Rhipicephalus sanguineous), others, on the other hand. Are more opportunistic, feeding on the blood of birds, reptiles, or mammals. According to their encounters (telotropic species, such as Ixodes Ricinus). Some species live in houses, closed places, close to the host species on. Which they depend (endophilic ticks), while others live outside, in open environments, such as brush. Meadows and undergrowth. They are then called exophiles.
Horse ticks (and other equines)
The ticks we encounter on our equines are not species specific. In Europe, there are essentially 4 species: Dermacentor reticulatus, Dermacentor marginatus, Ixodes Ricinus and Rhipicephalus bursa. They are all opportunistic species, Ixodes Ricinus being able to parasitize more than 300 different species of vertebrates.
Ixodes Ricinus is the most common tick in France. The highest populations are observed in regions with a rather cool and humid climate. They are much less frequent around the Mediterranean as well as at altitude (above 1000m) (Perez-EID, 2007). Dermacentor reticulatus shares the same type of environment as Ixodes Ricinus, ie cool and humid environments. Dermacentor marginatus and Rhipicephalus bursa, on the other hand, prefer hot regions with a dry climate. Such as the south and south-west of France.
Unlike fleas and lice, ticks are transient parasites, alternating free life in nature and parasitic life on their host. After the eggs hatch, their life cycle includes 3 successive stages of development: larva, nymph, and adult. The 3 stages each perform only one meal on their host. Which they then leave once sated by dropping to mount or lay eggs on the ground. This blood meal, which lasts between 5 and 10 days. Is essential for larvae and nymphs to molt to the next stage.
If the blood meal does not take place. The tick may remain at the same stage of development for a long time. Adults, it is mainly the females that will feed on their host. After being fertilized, on the ground or on their host, the female gorges herself one last time with blood (up to 200 times her weight!). Before returning to the wild to lay several thousand eggs and then die. Males most often die after fertilization.
Between two meals, they hunt on the lookout, perched on grasses, brushwood, or leaves, patiently waiting for a potential host, whatever it may be, to pass within its reach. The tick does not see (it has no eyes): it locates its host thanks to the sensory receptors (Haller’s organ) which it has on its front legs. It perceives the heat and odors emitted by the host (carbon dioxide, ammonia) as well as the vibrations of the ground when the latter moves. The tick does not jump it clings in a fraction of a second to the skin or coat using claws as soon as the host brushes against the plant that carries it.
Each stage corresponds to a particular hunting zone: the larvae hunt close to the ground (between 0 and 15cm in height), close to their place of hatching, where the humidity is higher (plant litter). They mainly infest rodents and small animals (lizards, birds), but can occasionally infest larger mammals if they pass within their reach. With a size of less than one mm, they are very difficult to see with the naked eye. The nymphs have a wider hunting range, taking advantage of their first host as a means of transport.
Perched on the vegetation at less than 50cm in height, they are thus frequently found in horses, at the level of the nose, the trough, the muzzle, and the limbs, taking on the appearance of a black and spherical pinhead 1 to 2 mm once engorged with blood. The adults, 5 mm in size on an empty stomach, can be detected easily, but are most often detected when already engorged with blood. Perched up to a height of 1m50, they are most often found on the head, chest, neck, ars, crotch and genitals.
Whatever their stage of development, tick activity is maximum when outside temperatures are between 5 and 25°C: spring and autumn are therefore particularly favorable seasons for tick attacks. Below and above these temperatures, their activity decreases, until they become completely lethargic in the most extreme conditions (temperatures below or above 35°C, or in the event of drought). Taking refuge in the ground, under leaves or dead wood, ticks can wait a long time for the return of milder conditions.
Ticks on horses are very resistant and can live for a very long time (several years), when young, or if the external conditions are not met. As soon as temperatures rise to 5-7°C, tick activity resumes. We can therefore find ticks at each of the stages throughout the year, especially in the event of a mild winter or a humid summer. The life cycle of a tick can thus varies from a few months to about ten years, depending on climatic conditions and the disposition of hosts.
The sting/bite – feeding system:
Once on its host, the ticks move in search of a place where the skin is particularly thin, moist and vascularized. Thanks to their chelicerae (cutting mouthparts), they incise the skin and introduce their rostrum deeply to suck the blood released by the broken blood vessels. At the same time, their salivary glands secrete numerous substances facilitating their meal: anticoagulants, vasodilating substances and enzymes which will liquefy the tissues at the level of the wound.
The bite is painless, the tick also injecting an analgesic substance. During the meal, she will regularly regurgitate excess liquid. This is when the tick runs the risk of transmitting pathogenic agents to its host if it is infected, regardless of its stage of development.
Ticks, vectors of disease
The risk of contamination is thus greater as the tick grows and feeds on different hosts. But infected females can also transmit their pathogens directly to the next generation when laying its eggs. The larvae, although never having bitten an infected host. Can therefore also be responsible for the transmission and spread of diseases. The passage of infectious agents can also occur from the male to the female during mating.
On the other hand, ticks are very frequently co-infected by several pathogens at the same time. And can therefore transmit them to their host during a single bite, thus complicating the diagnosis.
In France, piroplasmosis is mainly present in the south of the country. But also in the Rhône and Saone valleys, in Normandy. Horses born and living in an infested area develop some immunity to piroplasmosis. And rarely show the acute form of the disease. If the “chronically ill” show a few discreet symptoms (slight anemia, fatigue. Loss of weight and appetite or reduced performance). The “healthy carriers” tolerate the presence of the parasites perfectly. These horses can retain the parasite in their blood or deep organs (especially the spleen). For a very long time and are infective to vector ticks.
Horses suddenly transported from an uninfected area to an infested area are very susceptible to infection. And develop the disease in an acute form. Symptoms are serious but non-specific: fever (very marked at the beginning. Which can exceed 40°C), anemia due to the destruction of red blood cells. Dark urine due to the elimination of bile pigments, jaundice, edema of the limbs, depression, and fatigue.
The acute form is sometimes fatal. Especially in old horses or horses with heart failure, if no treatment is put in place. Horses, when they recover. Often remain chronic carriers of the parasite for several years and may re-develop a new acute form,
Means of fight and prevention: Prevention is better than cure
The best way to prevent tick-borne diseases is to avoid the bite: The first hours (especially the first 24) are indeed decisive in the transmission of pathogens, often long before ticks are spotted once they have been swallowed. of blood.
One of the first things to do is to remove brush, tall grass, and shrubs from the meadow. As well as low vegetation on the edge of woods or forests (low branches of deciduous trees, ferns, bushes, etc.).
The application of a greasy and film-forming ointment can be an effective first barrier. Especially for nymphs and larvae, which are not very visible. It will limit the attachment of ticks and their movement on the skin and hair and will asphyxiate the larvae. Apply the cream to sensitive areas with thin skin, head, and limbs.
The application of an acaricide, such as pyrethroids or organophosphates. To the horse’s skin can constitute an effective preventive solution, but of short duration (2 to 3 days). Indeed, On the other hand, few products have a marketing authorization for the elimination of ticks on horses in France. But the use of insecticide substances in the external environment is not desirable. It raises effect of environmental pollution, ecosystem imbalance and resistance problems.
Acaricidal active substances have a broad spectrum of action against cold-blooded animals (insects, reptiles, and aquatic organisms).
If unfortunately, your horse is host to a tick. Be sure to remove it using tick tweezers or a tick remover for cats. This is currently the safest way to remove the parasite without harming the animal. Because otherwise the tick’s head can remain stuck in the skin.