ixodid ticks

Ixodid ticks (Ixodidae) are one of the most famous human parasites and, perhaps, the most recognizable among all their relatives. Moreover, at first glance it may seem that there are not so many reasons for such fame.

Ixodids are not the most numerous group in the subclass: there are only about 900 species of them among 54 thousand species of ticks in general. They are not of such great economic importance as other types of mites, such as spider mites, leading to huge crop losses in different countries. Yes, and in terms of epidemiological significance, ixodids are inferior to their other relatives - dust mites, which cause millions of cases of asthma around the world, scabies (causative agents of scabies) and acne glands, parasitizing literally on every adult on the planet.

Nevertheless, ixodid ticks are well known and greatly feared - primarily because of their ability to infect humans with deadly infections that are relevant not only in the taiga, but also in urban areas. Parasite-borne encephalitis and Lyme borreliosis kill and disable hundreds of people worldwide each year, and many pets die from veterinary infections.

But in addition to the epidemiological significance, ixodid ticks are very interesting due to the unique features of their biology and interaction with their hosts. We will consider many of these nuances in more detail ...

 

Family members

The family Ixodidae, despite the relatively small number of species included in it, is distinguished by a significant diversity of its representatives both in appearance and (to a greater extent) in lifestyle.

One of the most typical and well-known representatives is the taiga tick Ixodes persulcatus, which lives mainly in the northeastern regions of Russia and is a carrier of spring-summer tick-borne encephalitis here. With the onset of the warm season, its nymphs, after wintering in the forest litter, begin hunting for small mammals and reptiles, and adult adults look for large animals (or humans) to feed on.

The photo below shows adult representatives of this species:

Another, similar species - Ixodes ricinus, or dog tick - is more typical for the European zone. It is found in deciduous and mixed forests and is active mainly in spring and autumn. Its adults parasitize on livestock, dogs, hares and humans. It is these ticks that are responsible for the infection of the so-called western form of encephalitis and Lyme borreliosis in Europe.

Species of ixodid from the genus Dermacentor, recognizable by the white enamel pattern on the dorsal shield and also living in Europe and the European part of Russia, are the main carriers of tularemia and tick-borne typhus:

On the Black Sea and Caspian coasts, a brown dog tick is common, which can carry Marseille spotted fever. At each stage of development, such a tick feeds only on dogs, however, a person can become infected if he crushes the tick and then infects the mucous membranes of his mouth, eyes or nose himself.

Photo of a brown dog tick:

Interesting, but less familiar to the general public, are some other ixodids:

• The Ixodes holocyclus tick is found exclusively on the east coast of Australia. It has an interesting feature - the high toxicity of saliva secreted into the wound during bloodsucking. Its neurotoxin is so strong that it can lead to paralysis and death of victims - kangaroos, koalas, dogs and even humans.;
• The Ixodes uriae tick is an inhabitant of the lowest latitudes among all Ixodes. Its typical hosts are birds nesting on the Arctic and Antarctic islands, as well as on the mainland coasts of the Arctic and Antarctic. Due to the very short nesting period of their host birds, these ticks go hungry most of the year, simply biding their time hiding in rock crevices, burrows and old nests along the coasts;
• The camel tick Hyalomma dromedarii is one of the most common in North Africa, and therefore tourists in Egypt may well encounter it. The main preferred hosts are camels, but hungry individuals do not disdain other animals. A person usually develops necrosis around the site of the bite, but with proper treatment, it fortunately heals relatively quickly;
• Ixodes lividus is a specific parasite of sand martins that lives right in their nests. Its life cycle is closely related to that of host birds: ticks actively feed on blood in spring and summer, and starve all autumn and winter and patiently await the return of their hosts in their own nests;
• Representatives of tropical Amblyomma species are ixodid ticks, which are distinguished by their large size and phenomenal fertility. The blood-sucking female can reach the size of a plum, and is able to lay up to 30,000 eggs.

The photo below shows the pig mite Amblyomma sculptum:

On a note

Due to the fact that most ixodids parasitize a wide range of hosts, scientists are still arguing about their origin and evolutionary relationships within the family. Some believe that ixodid ticks were originally parasites of reptiles, and only then began to move to mammals. Others claim the opposite - that just mammals became the first owners of ixodid.

Today, the family is systematically divided into two groups, one of which includes, in fact, the genus Ixodes, and the other includes all the rest. But the lack of data on fossil species still leaves open the question of the taxonomy of the group of ixodid ticks.

 

Appearance and anatomical features of ixodid ticks

The appearance of ixodid ticks is quite recognizable. Adult representatives of most species in a hungry state reach a size of about 5 mm, and their body is strongly flattened in the dorsal-abdominal direction.

In the structure of the parasite, a gnathosoma is distinguished - a “head”, which is actually a complex oral apparatus, as well as an idiosoma - in fact, a body to which 4 pairs of legs are attached. This detail of description is very important and helps to distinguish the parasite from other arthropods by its appearance.

The photo below shows a gnathosoma in an engorged female:

Ixodid ticks have olfactory organs on their legs, and therefore they usually wait for their prey by putting them forward. Also on the body and legs there are many bristles that help to stay on different surfaces, serve as an element of protection and help in resettlement.

Adults have differences in morphology, depending on gender - females have only a small shield on the back, while in males the shield covers the entire back.This is due to the fact that females feed much more intensively, and a large shield - a solid chitinous formation - will interfere with the stretching of the body when sucking blood.

On a note

It is worth noting that stretching occurs due to a special cuticle that completely covers the body of the tick. In a hungry individual, this cuticle contains many microfolds and grooves, which straighten out during saturation, and the body increases, acquiring a rounded shape and a grayish tint. The color of a hungry tick can vary from yellow-brown to almost black.

The mouthparts of ixodid ticks are ideally suited for feeding on blood on hosts with dense body integuments. It consists of a base, a proboscis, one pair of sheathed chelicerae, and a pair of palps. The base of the proboscis is a capsule with a dense chitinous cover, where the ducts of the salivary glands are located. Palps consist of 4 segments and perform a tactile function.

The hypostome, or proboscis, is a rigid chitinous plate fixedly attached to the base. On it are rows of sharp, backward-curved hooks that help to cut through the skin like a saw and get fixed in it like a harpoon.

The victim usually does not even notice the bite process, because the saliva of the parasite contains painkillers that act on the nerve endings almost immediately.

In addition to painkillers and blood anticoagulants, tick saliva also contains a special protein secret that freezes around the proboscis that has penetrated. This provides additional reliability when fixed in the skin - a kind of "cement case".

 

Lifestyle and habitats

Ixodid ticks are mainly pasture parasites, waiting for their hosts in the open nature.For life, they prefer mixed forests and clearings with high grass cover. The process of their "hunting" is usually passive - ticks almost never deliberately pursue potential victims, they simply wait for the right moment to cling to wool or clothing.

Ixodid ticks are generally very slow - in their entire life, each individual passes no more than a couple of tens of meters.

At each stage of development, the parasite needs to feed only once; therefore, having satiated itself on the host, it disappears, and only in some cases can remain on the host's body to pass to the next age. Ticks overwinter mainly in the forest litter, sometimes in burrows of their hosts or even on them.

Species that have adapted to specific burrow parasitism often find it much easier to find food, because blood sources are almost always nearby. Such, for example, is the tick Ixodes laguri, which lives in rodent burrows.

It is interesting

In certain cases, strict specificity in the choice of prey severely limits the rhythm of life of the tick itself. For example, Ixodes uriae, which has adapted to living in rock crevices in bird markets, can only feed during nesting birds, and starves the rest of the year. Due to the peculiarities of the geography of its habitat, this species parasitizes even on penguins.

 

Distribution of ixodid

Ixodid ticks are ubiquitous and are found on all continents of the globe. But, as with any organisms, they have their own limiting factors. First of all, it is the need for optimal temperature and humidity.Even in the same forest in its different parts, an unequal microclimate prevails. In meadows open to sunlight, there may not be enough moisture for the normal activity of ticks. And, for example, at the edge or in the thicket of the forest, there may be plenty of water. Therefore, the distribution of ixodid in any geographical area is discontinuous, mosaic.

The presence of suitable hosts is also important, but Ixodes are highly flexible, and therefore often able to survive almost anywhere terrestrial vertebrates live.

Altitude is also not a serious limitation for ticks: they are found in all altitudinal zones - from sea level to high mountains. For example, Ixodes acutitarsus is often found in the Himalayas above forest level.

However, the greatest diversity of ixodid ticks is observed in subtropical and tropical latitudes. The farther away from them, the fewer species of ixodid can be found.

One of the most famous ticks - taiga - has a distribution within the boundaries of the range, limited by Kamchatka and Sakhalin from the north, and the Moscow region - from the south. Its relative, the dog tick, is found in North Africa and throughout Europe, reaching the Volga itself. The brown dog tick, as already mentioned, prefers coastal areas, including the Crimea and the Caucasus. It is these species that pose the greatest epidemiological danger to residents of Russia and European countries.

 

Hosts of different types of ixodid ticks

In the life cycle of ixodid there are three active stages - larva, nymph and adult, and at each stage the tick feeds only once. Some species attack a new host at each stage.Such, for example, are the taiga and dog ticks - the range of species of their victims depends on the stage of development of the parasite itself.

Larvae and nymphs feed on rodents and birds, while adults prefer large mammals, including humans. Such species are called three-hosted, since at each of the three stages of development the parasite must find a new animal.

There are also two-host ticks - this means that the larva, having sucked blood, does not leave its first host. Turning into a nymph, she bites him again, and only after that falls away from the first victim. The third time an adult tick will bite another animal.

Hyalomma marginatum is a typical example of such a parasite: the larva, and then the nymph, feed on the first host (a rodent or bird), and after molting and turning into an adult, they feed on the second one, which can be either a cow or a horse, or a person.

In single-host parasites, the tick will not leave its first and only host until it reaches the adult stage. An example of this is the Mediterranean species Boophilus calcaratus, which is widespread, including in the south of Ukraine. The larvae attack an animal (usually a large mammal) and go through all further stages of development directly on it. The females, already drunk with blood, leave the host to lay several thousand eggs on the soil. This feature allows you to increase the survival of the species, because here you do not need to wait as many as three times for a meeting with a potential victim.

Interesting fact

Among ixodid species there are also species with a narrow specialization - feeding only on birds, reptiles or mammals. For example, the tick Hyalomma aegiptium prefers only terrestrial turtles as hosts in all phases of growth.But Amblyomma sphenodonti is a unique species in several respects at once. Firstly, it lives exclusively in New Zealand, and, secondly, it feeds only on tuatara - the oldest type of reptile, "living fossils" of our time. One can only imagine how many thousands of years such a close relationship of hosts and parasites lasts. The photo below shows ticks between the scales of the tuatara:

The duration of the tick's feeding period increases with each subsequent stage of development. Larvae can attach to hosts for 3-5 days, nymphs - for 3-8 days, and adults are saturated with blood up to 10-12 days. At the same time, the influence of ticks on an animal depends on many factors: the susceptibility of the host, its mass and the general degree of infestation.

Often, severe tick infestation leads to mass mortality of livestock. For example, 3-4 female ticks per 1 kg of body in an ordinary sheep are already a threat of an imminent lethal outcome.

If too many ticks are sucked on the animal, this entails large blood loss and acute intoxication with saliva. Ixodid saliva contains many proteins that can cause severe immunological reactions. In addition, tissue damage in the area of ​​the bite can result in suppuration and additional infection, not to mention diseases that can be transmitted by the ticks themselves.

 

Nutrition specifics

Before starting to suck blood, the tick usually looks for a suitable place on the host's body for a long time. He will definitely prefer an area with delicate thin skin, so often ticks are found on the neck, behind the ears, in the groin, on the folds of the limbs.

Having found a good area for a bite, the parasite rests the anterior part of the body against the skin and assumes a position almost perpendicular to it, piercing the chelicerae.This process is not instantaneous, and the drilling of the integument of the host itself can take several tens of minutes. Gradually, the chelicerae are introduced deeper and deeper and push the wound apart from the inside, allowing the proboscis to penetrate the skin. Inside the proboscis there is a preoral cavity where the salivary glands exit, and saliva is actively secreted into the wound zone.

If the tick is infected with any infection, then already at this moment the pathogens will begin to penetrate into the tissues of the host.

A special protein component - saliva secretion - quickly hardens, creating an intermediate "cemented" zone between the proboscis and host tissues, additionally fixing the tick's mouthparts in the skin. At the end of the "cement case" multiple hemorrhages and an inflammatory focus are formed, but the parasite's saliva also contains anesthetics, and therefore the bite often goes unnoticed.

In addition, saliva contains vasodilators and components that prevent blood clotting (anticoagulants). All this is necessary to ensure successful long-term nutrition of the tick.

An interesting fact is that bloodsucking is not a continuous act of food entering the organism of the parasite. In the process of blood suction, the stages of active saturation and rest alternate. In the preoral cavity of the tick, thanks to the muscles of the pharynx, a vacuum is created that acts as a pump for blood and lymph during their absorption. Having fed, the tick takes the proboscis out of the body and disappears.

On a note

Ixodids have some amazing features of biology that are characteristic only for some representatives.One of them - aphagia - is a phenomenon in which adult males of certain species do not feed at all, but are only engaged in the fertilization of engorged females, after which they immediately die.

Another interesting phenomenon, characteristic only for ticks, is omovampirism, in which hungry ticks (usually males) do not disdain attacking their well-fed relatives. They pierce the body of a fellow and suck some of the blood from it. What is remarkable: the victim tick remains alive after such an unceremonious interference in its metabolic processes, and if it is a female, then she is quite capable of safely laying eggs after this.

 

Reproduction and development

It is not easy to give a general description for all ixodids in terms of reproduction and development. They have a huge variety of life cycles in terms of the total duration and seasonal activity of hungry individuals. All three active stages can develop during one warm season, sometimes even several generations are formed during this time. In other cases, the transition from egg to larva, nymph, and then adult requires a lot of time, and the cycle stretches for up to five years.

The total duration of bloodsucking on the host during the entire life of the ixodid tick reaches a total of about 15 days, which is an extremely small fraction of the total duration of ontogenesis. But during this time, serious qualitative changes occur in the body of the tick, associated not only with the stretching of the integument of the body during feeding, but also with the development of its body as a whole. Due to this, after saturation, the larva becomes a nymph, and that, in turn, an adult.

As already mentioned, at different stages of development, ticks attack animals of different sizes. If in the first two stages small rodents, reptiles and birds become victims of most ixodids, then adults already prefer large animals, including ungulates and humans.

Depending on how many hosts a tick changes in its lifetime, the types of parasitism and the proportion of surviving individuals differ. Three-host ticks survive worse than two- and single-host ticks, because they are forced to leave the previous victim after each act of feeding, and it is often very difficult to find the next one. Therefore, at the stage of larvae and nymphs, such ixodids die en masse. Although this does not apply to nesting and burrowing parasites, which actually share a dwelling with their hosts, and are more likely to be provided with food.

The reproduction of ixodid ticks is also not without interesting details. The search for a partner and the mating itself most often takes place right on the owner. This is explained by the fact that the search for each other in nature is extremely difficult due to the solitary lifestyle, wide habitat and low mobility.

In addition, individuals of some species are generally incapable of mating without having fed on blood. Therefore, the ideal place for a “date” is just at the meal. On the 3rd-5th day of bloodsucking, adult ixodid females begin to secrete special compounds - pheromones, which attract males.

Mating is carried out right during the feeding of the female, which she does not interrupt for several more days after insemination. The male either dies immediately after mating, or may consume another portion of blood and go looking for a new female.

By the way, the nutrition of ticks differs depending on gender.In general, all Ixodes are characterized by a much shorter suction of males to the host compared to females - they only need a couple of hours to saturate. And the body of males itself is not adapted for large volumes of blood - it is surrounded on all sides by rigid inextensible shields.

After the fertilized female is fed enough blood, she falls away from the host and prepares for the process of laying eggs. Their maturation takes from several days to a month, and is due to the nutrients obtained from the blood of the last victim.

The laying process itself is also long - from three weeks to two months. At the same time, a female dog tick will lay an average of 2000-3000 thousand eggs, but individuals of more exotic tropical species - up to 20 thousand eggs, and sometimes even 30 thousand or more.

 

Why are these parasites dangerous?

Ixodid ticks are dangerous, first of all, as carriers of many infectious diseases, and therefore are of great medical importance. In terms of the variety of transmitted infections, they are ahead of all arthropods, including mosquitoes.

About 100 viruses, 200 species of piroplasmids, dozens of species of rickettsia, trypanosomes and bacteria were isolated from ticks collected in nature. But still, infection with certain infections is not the norm for ixodid - ticks become infected with them either when feeding on a sick animal, or even in an egg from an infected mother.

With rare exceptions, a breeding pathogen does not cause any harm to the tick, unlike its possible host.

The most common and significant infections carried by ticks are:

• Tick-borne encephalitis is one of the most dangerous diseases, often ending in death.It is caused by a virus that actively multiplies in the cells of the nervous system, causing severe damage to it, up to paralysis. There are several subtypes of this infection, and some of them are mild, while others are very difficult and with complications;
• Lyme borreliosis is a bacterial disease. The symptoms are very varied: fever, headache, fatigue, nausea. A characteristic sign is ring-shaped redness around the tick bite (erythema migrans). If the disease is not cured at the initial stage, severe damage to the brain, cardiovascular system and joints, with a possible fatal outcome, joins the symptoms;
• Tick-borne typhus is a disease caused by rickettsiae. They multiply in the vascular endothelium, causing an inflammatory response in the body. This process is accompanied by high fever, rash (first on the limbs, and then all over the body), swelling of the face, swollen lymph nodes. Often ends in complete recovery;
• Piroplasmosis - rarely transmitted to humans, but very dangerous for pets. It is caused by piroplasms - parasites that destroy red blood cells. The disease begins acutely, with a sharp rise in temperature, the animal stops eating and drinking, often lies down. In the absence of proper treatment, death occurs in less than a week.

The photograph below shows erythema migrans, a characteristic sign of Lyme disease:

It is important to note that even uninfected ticks, with a large number of them on one host, cause him great harm. Wounds from the penetration of ixodid proboscis can additionally become infected with pathogens from the surface of the skin or from the air. Such lesions can then fester and not heal for a long time, causing severe discomfort.With an impressive number of sucking ticks, the host also begins to suffer from blood loss. This poses a risk of developing anemia that is incompatible with life.

 

Ways to protect against ixodid ticks and fight them

There are several effective ways to protect yourself from ixodid tick bites in nature. The simplest thing to do is to dress appropriately when going into a potentially dangerous area. For this, shirts with a high collar and long sleeves with tight cuffs, long trousers and, if possible, closed high shoes are suitable.

It is advisable to tuck trousers into socks, and a shirt into trousers. It is also good to use smooth and light-colored fabrics in clothing, for which it is more difficult for a tick to catch on and on which dark ticks are clearly visible.

Among active control measures, spraying clothing and animal hair with repellents containing diethyltoluamide (DETA), dimethyl phthalate, repudin, diethyl phthalate, carboxyl, repephtal and others is effective. For animals, there are also tablets and injectable preparations that provide resistance to tick bites for a certain time.

Among folk remedies, self-prepared protective sprays are popular. They are made from natural essential oils, vinegar or strong-smelling ointments, mixed with water. Perhaps they have some effect, but a person needs to be prepared to endure the annoying smell of the product himself, which is not suitable for everyone. In any case, in terms of the strength of the protective effect, such preparations are for the most part inferior to those based on powerful synthetic repellents.

Upon returning from a park or forest, it is useful to conduct self- or mutual examinations for the presence of ticks - this way you can quickly get rid of parasites that have not yet had time to stick to the skin. If the tick was nevertheless found already attached, then it is necessary to remove it with tweezers or fingers wrapped in gauze. Remove the parasite with light rotational movements, trying not to tear the body from the head and not crush the tick itself.

At the same time, it is important not to try to pull out the tick with a simple tearing movement - in this case, you can tear off its body from the head, which will remain in the skin and lead to suppuration.

In regions where cases of tick-borne encephalitis have been repeatedly reported, there is a well-established system for the prevention of this disease. It includes both vaccinations and emergency care immediately after being bitten by an infected tick.

If desired, you can take a vaccination course of several vaccinations following one after another in a strict time relationship. This course provides reliable protection against the disease, but vaccination must be repeated periodically, because immunity to encephalitis after it lasts only about a year.

If a tick infected with the tick-borne encephalitis virus has already bitten, and the person has not been vaccinated before, then an emergency injection of anti-encephalitis gamma globulin will be effective during the first three to four days. This protein specifically binds to the pathogen and prevents the disease from developing.

Garden plots can be expedient to process for the destruction of ticks on them. To combat ixodides, special acaricides are used - in large areas they are sprayed with the help of aviation, in small areas - with manual and motor sprayers.

On a note

In the past, long-acting preparations such as DDT (dichlorodiphenyltrichloroethane) and HCCH (hexachlorocyclohexane) were widely used as treatments. They showed high efficiency in the destruction of ticks, but also turned out to be dangerous for the environment and the people themselves.

Today, in order to get rid of ticks in the territories of sanatoriums, recreation centers and children's camps, safer drugs are used: karbofos, trichlorvos, chlorpyrifos, fenthion, permethrin, cypermethrin and others. It is preferable to poison ticks with the help of professional exterminators - they have access to modern effective drugs and know how to use them correctly.

Control over the number of ticks helps to maintain and their natural enemies in nature. Here predators often feed on ixodids, the diversity of which is quite large: spiders, beetles, ants, wasps, centipedes. They are also eaten by amphibians, reptiles and birds, and the latter can even eat wintering ticks in their hiding places. That is why it is useful not only to treat the site with acaricides, but also to make it attractive to natural enemies of ticks.

 

Interesting video: curious facts about ixodid ticks ...

 

Efficacy test of various tick protection products