Ticks have opened their season in Moscow – Kommersant FM

Moscow, 03/03/2021, 20:41:34, editorial office PRONEDRA.RU, author Ekaterina Pavlova.

Tick-borne encephalitis is one of the most well-known diseases, but not the only one that is transmitted by insect bites, namely ticks. In 2021, 1,910 cases of infection with this disease were recorded, including 201 children. If you resort to official statistics: every year from 30 to 40 people die from diseases transmitted through tick bites.

Looking at these numbers, you may get the impression that this problem will never affect you. But it is worth considering, for the time being, not a single person is immune from this. When a tick bites you, your perception changes dramatically, at which point you remember statistics that no longer seem harmless.

Don't date a "foreign" parasite

The choice of methodological approaches to the study of the infection transmission system was based on the experience of studying natural foci of TBE, accumulated by that time, mainly by Soviet science. As is known, the TBE virus can live and multiply in the bodies of different animals, but in the transmission of the virus from an infected to an uninfected individual, a key role is played by natural carriers - two species of ixodid ticks: taiga ( Ixodes persulacatus

Schulze) and forest (
Ixodes ricinus
L.).

In the Urals, Siberia and the Far East, only the first of them is common. In general, ticks of the genus Ixodes

a complex development cycle that includes three stages. At each stage of its life, a tick, together with the host’s blood, can either itself receive the TBE virus and other pathogens of vector-borne infections, or, conversely, infect the host with the virus through the secretion of its salivary glands.

It is important to note that in the natural hosts of the tick, infection with the TBE virus does not cause the usual clinical symptoms, which is not surprising: after all, the co-evolution of the parasite (in the broad sense of the word) and its host most often goes in the direction of reducing the negative impact of the parasite on the host’s body (Thompson, 1994). The tragic consequences of human contact with the encephalitis virus are largely explained by the fact that, by and large, it is a “newcomer” in this “host-parasite” system.

Did you know that tick-borne encephalitis virus can be sexually transmitted in mammals? At least, this phenomenon was discovered when crossing infected male laboratory mice with healthy females (Gerlinskaya et al., 1997)

Taking into account the life cycle of the tick and its connections in the biological community, the researchers selected the main objects and methods of monitoring. The abundance and degree of TBE virus infection in adult ticks were assessed; the number and degree of tick infestation of small mammals, as well as the presence among these individuals of so-called seropositive individuals, i.e. those containing antibodies to the tick-borne encephalitis virus in the blood.

In addition, from the very beginning, the biological activity of the virus isolated from adult taiga ticks was studied, and since 1990, the immunity of background species of rodents, the main hosts of the tick in the early stages of its development, began to be assessed. In parallel, in joint research by employees of the Institute of Life Sciences and Life Sciences and the Institute of Chemical Biology and Fundamental Medicine SB RAS, molecular biological methods were developed and tested using collected field material for highly sensitive and specific indication of the TBE virus (Bakhvalova et al., 1989; Bakhvalova, 1994; Morozova et al. .

, 2002).

Over 27 years of continuous monitoring, the features of the distribution and long-term dynamics of the taiga tick in the forest park zone of the Novosibirsk Scientific Center, the species composition of small mammals were studied (Sapegina et al., 1985; Dobrotvorsky, 1992); a unique collection of TBEV strains was formed, which, based on nucleotide sequences, were assigned to the Siberian genetic type (Bakhvalova et al., 1994, 2000, 2001; Bakhvalova et al.

, 2000).

Description and causes of the disease

This disease is of an infectious nature, affecting the brain matter of both the head and back. The disease is transmitted to persons exposed to the bites of infected insects - ticks. The main habitat areas of the isolated species of ixodid ticks are the territories of Siberia, eastern Russia, northern China and Mongolia. There are cases recorded in the countries of Eastern Europe and Scandinavia.

The pathology has a clearly demarcated seasonal nature - the spring-summer period. According to statistics, every year transmission insects infect about 5-6 thousand people with the encephalitis virus. The main cause of the development of neurological pathology is a microscopic virus of the flavivirus genus. It is much smaller in size than, for example, influenza or measles viruses, which allows it to easily bypass any immune barriers of the human body.

When in an open space at high temperatures or under the influence of UV rays, the virus quickly disintegrates and dies, but in a cool climate it can remain viable for a long period of time. If you do not boil the dairy products of an infected animal, the virus remains active for about 60 days. Under natural conditions, the pathogen is fixed in the bodies of ixodid insects, spreading through their bites to humans, small and large domestic animals. You can become infected with the aggressor not only through a bite, but also through direct contact with a tick - by accidentally crushing it with your hands, or by eating meat or dairy products that have not been thermally treated.

The number of encephalitis carriers increases in the spring and autumn, and periodic outbreaks of morbidity in risk areas are associated with this. Parks, walks in the forest, tourist centers and trail routes become dangerous places.

The gradation of pathology depends on the predominant signs of manifestation:

febrile form - develops in half of all recorded cases;
meningeal form - affects a third of all patients and is characterized by a disorder of the functionality of brain structures;
focal type - focal neurological symptoms predominate, individual areas of the brain substance are affected (noted in 20% of those infected).

Incubator for infection

After 10 years of observation of the encephalitic lesion under study, things were discovered that did not fit into generally accepted patterns. It would seem that what can serve as a measure of infectious risk if not the number of ticks and the degree of their infection with the virus? However, the usual criteria for encephalitis danger were far from corresponding to the reality expressed in the dynamics of encephalitis in residents of the Sovetsky district of Novosibirsk, where Akademgorodok is located.

At the same time, it was possible to establish that 1-2 years before the peak of human morbidity, the largest possible number of larvae and nymphs, the early stages of the taiga tick, are found on the skin of small mammals; Moreover, among tick hosts there is a large proportion of seropositive individuals, i.e. animals whose blood contains antibodies to the tick-borne encephalitis virus. What consequences might these two interrelated events have?

As is known, survival and reproduction of the virus in the body of the ticks themselves leads to a decrease in virulence

, i.e. the ability of the virus to cause disease. However, this property is quickly restored if the virus enters the body of a warm-blooded animal, where it begins to multiply (Chunikhin et al., 1982). Therefore, when the proportion of infected individuals among small mammals increases, the likelihood that tick larvae and nymphs will receive a highly virulent strain of the disease pathogen during their bloody meal increases sharply. After 1-2 years, these larvae and nymphs will turn into adult ticks, in whose bodies the most “aggressive” virus will function: their bite poses the greatest danger to us in terms of infection with encephalitis.

The fact that the dynamics of human morbidity is largely determined by changes in the virus itself was confirmed by studies of its infectious properties: hemagglutinating activity

(GA) and virulence of viral isolates isolated in different years. It turned out that long-term fluctuations in HA coincide with fluctuations in the incidence of residents of the Sovetsky district; and the virulence of isolates obtained during years of high incidence is significantly higher than that of isolates isolated during low incidence (Bakhvalova, 1994; Bakhvalova, Dobrotvorsky, 1994; Moshkin et al., 1998; Bakhvalova et al., 2005).

So, monitoring individual components of an encephalitic focus for several years based on relatively simple parameters - the degree of infection of small mammals with ticks and tick-borne encephalitis virus - makes it possible to quite accurately predict the notorious encephalitis “epidemics”. But this prediction, although quite sufficient for predicting infectious risk, is a rather simplified description of reality. In recent years, thanks to the development of molecular genetic methods for identifying pathogens, the role of small mammals in the circulation of tick-borne infections has been reassessed. What have we been able to learn about this eternal, like the world, and seemingly inexhaustible natural reservoir of infections?

How to fight the disease?

The sick person is subject to immediate hospitalization, but is not isolated in the infectious diseases department, since the patient does not pose a danger to others, but is treated as an inpatient in neurology. Restorative manipulations are aimed at suppressing the viability of the flavivirus, blocking the spread of the pathogenic process in internal tissues and organs, and reducing symptomatic manifestations.

Strict bed rest is mandatory. In the early stages of the lesion, the introduction of immunoglobulin, which is used for three days, is effective. Other immunomodulatory medications are also prescribed individually.

At the later stages of the development of the disease, pharmaceutical products of this group are no longer effective. Doctors try to maintain the patient’s viability in case of damage to nerve tissue. If respiratory function is impaired, artificial ventilation of the lungs, reduction of internal pressure (with diuretics), antipsychotics and substances aimed at making the brain more resistant to hypoxia are carried out.

Testosterone detonator

Judging by the monitoring results, the dynamics of the encephalitis danger of a natural outbreak is largely determined by changes in the virus population. These changes, in turn, are caused by different amounts of contribution to the reproduction of the virus by its main “hosts” - the taiga tick and warm-blooded hosts.

In particular, in joint studies with IHBFM it was found that viral RNA and/or the envelope protein of the tick-borne encephalitis virion (indicating the presence of a virus) are found in the organs of the vast majority of small mammals (Bakhvalova et al., 2001; Bakhvalova et al., 2003; Bakhvalova et al.

, 2006).
Moreover, this phenomenon is typical not only for animals caught during the tick-active season, but also for animals caught in winter or kept in a vivarium for a long time after capture, i.e., obviously “free” from ticks. This means that in the body of wild mammals the virus can persist for a long time in a persistent
(surviving) state, as a rule, without manifesting itself in any way. At the very least, it is not capable of infecting two-week-old laboratory mice, which are usually susceptible to this virus.

SHOWER AND ANTIPERSPIRANT AGAINST TICKS
What is the hunting strategy of female taiga ticks based on? As already mentioned, they prefer to feed on adult territorial males, whose immunity is suppressed by high levels of the male sex hormone testosterone. Urinary marks, which territorial males constantly use to mark their individual areas, can act as an odor signal. The basis for this statement is experimental data obtained during the study of the behavioral response of ticks to various odor stimuli of warm-blooded animals. It turned out that the mite, moving freely along the edge of the Petri dish, does not react to fresh urine of a laboratory mouse (Romashchenko et al., 2006) or red-backed vole (according to the personal communication of A.K. Dobrotvorsky). However, if instead he is “presented” with bedding from a mouse cage with old (about 2-3 days) urine marks, then in 60% of cases the experimental mites exhibit a behavioral reaction, expressed in the desire to reach the source of the odor. It should be noted that the reaction of the mite to sweat samples from young men collected on filter paper also depends on the freshness of these samples. The most attractive smell for mites is the smell of sweat from the armpit area, and the strongest reaction is observed when the filter paper was under the donor's clothing for 2 days. An increase in the olfactory attractiveness of “stale” samples of sweat and urine may be a consequence of their bacterial transformation

However, this is not always the case. As our studies have shown, such a persistent virus can be activated when the host’s immune system is suppressed. Moreover, this can be done not only with the help of special pharmacological immunosuppressants, but also by introducing the usual male sex hormone - testosterone

(Bakhvalova et al., 2006).

And the last circumstance, as everyone understands, is especially significant: the fact is that the natural increase in the secretion of male sex hormones in mammals, including rodents, is timed to coincide with the breeding season. And it is combined with the suppression of the cellular and humoral immunity of individuals. Moreover, this period very precisely coincides in time with the period of greatest activity of ticks.

Another nuance: in the ecology of parasite-host relationships, there is a rule according to which 20% of the most infected hosts harbor 80% of the parasites of a particular species (Perkins et al.

, 2003).
According to our data, the distribution of red-backed voles ( Clethrionomys rutilus
Pall.) living in the studied TBE focus fully corresponds to this rule according to the degree of tick infestation. A natural question arises: what kind of individuals are these?

As is known, in a population of small mammals, individuals vary significantly in behavioral characteristics such as aggressiveness and territoriality. This difference in quality is determined mainly by differences in the secretion of sex hormones, and therefore, as mentioned above, and corresponding differences in the immune system of animals. The amount of contribution they make to the feeding of the taiga tick depends on this state of the individuals.

What did you find out? Among the most infected individuals, sexually mature sedentary males predominate, in which the magnitude of the humoral immune response to a standard antigenic stimulus is minimal. Compared to settling migrants, territorial males are characterized by a higher degree of infestation, which, at first glance, contradicts generally accepted ideas about the direct connection between the mobility of animals and the likelihood of their encountering ectoparasites.

Did you know that in the initial stage of infection, the tick-borne encephalitis virus causes an increase in aggressiveness in male rodents, as well as odor attractiveness to females?
Thus, these individuals increase the chance of leaving offspring (Moshkin et al.
, 2002)

But this is an apparent discrepancy. Firstly, the overall activity of males patrolling their individual territory may not be lower than that of migrants. Secondly, it has been experimentally proven that suppression of the host’s immunity, including through the administration of testosterone, increases the time and efficiency of tick feeding (Hughes and Randolf, 2001). And finally, the smell of urine marks, which a territorial male constantly leaves on the same routes, can be a more powerful “magnet” for ticks than the occasional urine secretions of spreading individuals: this means that the likelihood of encountering “prey” in this area is high!

Signs of infection with tick-borne encephalitis

Usually, a certain period of time passes before the first signs begin to appear - incubation of the pathogen, which takes 7-14 days. But in clinical practice, there are also cases when the first symptoms come to the fore within the first day after infection. It is extremely rare that patients experience their first complaints 30 days after contact with a tick.

During incubation, the viral aggressor multiplies intensively in the place where contact with the body occurred (a section of the skin or the inner wall of the gastrointestinal tract). As soon as the number of pathogens reaches a critical mass, it spreads throughout the body through the bloodstream. At this time, the body responds in the form of pathological symptoms. Further, the virus continues to multiply in the internal organs and central nervous system.

Regardless of the underlying form of the disease, the primary symptoms are the same:

a sharp, immediate deterioration in health;
influenza-like condition, manifested by convulsions, fever, pain in the muscles, head, weakness, lethargy, possible nausea and vomiting against a background of high temperature;
change in color of the skin of the face and neck towards redness;
expansion of the vascular network in the whites of the eyes.

Further, special signs characteristic of one or another form of the disease are recorded:

1. Febrile type of encephalitis. The name of the disease speaks for itself. The patient experiences a prolonged feverish state that lasts from two to ten days. The fever is periodic; after a period of high temperature, there is a short-term decline and improvement in well-being, which is again replaced by a strong increase in temperature. After a ten-day period, the signs of the disease disappear. During the first month, the patient may still complain of general weakness, aversion to food, arrhythmia, and increased sweating.

2. Meningeal type. It is characterized by clear signs of damage to the nerve membranes of the spinal cord and brain, which appear 3-4 days after the viral penetration into the blood. The symptoms are as follows:

unbearable pain in the head and neck area, not relieved by conventional analgesics;
repeated vomiting;
excessive sensitivity of the skin to external irritants, including clothing;
high tension in the muscular system of the cervical region and lower extremities, which leads to subsequent throwing back of the head in a side-lying position;
maintaining the legs in a bent state even when changing body position, the inability to straighten the legs independently;
When the specialist tries to tilt the patient’s head forward, uncontrolled bending of the legs at the knee joints occurs.

Meningeal symptoms are accompanied by the feverish state described above. These disorders progress over 14 days, then normalization occurs with continued sensitivity to light and sound stimuli, bad mood and weakness.

3. Focal type. The most severe form of encephalitis, as the virus penetrates and affects the internal tissues of the spinal cord and brain. The main symptoms are:

a sharp increase in temperature to forty degrees and above, drowsiness, delirium, severe chills and convulsions;
the appearance of hallucinations, loss of spatial and temporal orientation, disorder of consciousness;
as the pathogen further penetrates into the depths of the brain structures, respiratory and cardiac dysfunction may be observed;
tremor in the limbs, unsteadiness of gait;
Individual muscle groups are periodically paralyzed;
numbness in the areas for which the nerve roots are responsible.

There is also such a feature of the course of the disease as a two-phase focal type. At first, the disease occurs in a febrile form, followed by a “lull”, followed by a new wave of focal type. There is also a pathological type of disease - progressive. It is characterized by the development of persistent neurological disorders several months or years after acute encephalitis.

Is it worth getting vaccinated against their bites and insuring your health?

The tick season has started in Russia: the parasites have begun to attack people amid warming, Rospotrebnadzor warned. The agency says the situation is under control. Last year, a focus of encephalitis was discovered for the first time in the capital. What should Muscovites prepare for? And does it make sense to insure against ticks? Ivan Koryakin talks about this.

Along with Muscovites, ticks came out into the wild last weekend. And although there is still snow in the fields in some places, this is not a problem for them - it’s warm outside, unsuspecting people go for a walk, the season is open. Rospotrebnadzor employees recently caught several Moscow ticks. Nothing unusual so far: no one has become infected, the number of those bitten is within the normal range. And in general, fewer and fewer people are getting sick with encephalitis, although ticks can infect more than just that, says leading researcher at the Research Institute of Disinfectology Natalya Shashina: “Since this century, we have been living in areas of a steady decline in the incidence of tick-borne encephalitis. At the same time, the diagnosis of tick-borne borreliosis has improved, which is why its detection rate is increasing. This is a relatively new infection, widespread, but milder than tick-borne encephalitis. It is treated with antibiotics, but there is no vaccine for it.”

To defeat a tick, it is important to understand its logic: it crawls up the victim from the bottom up in search of open areas of the body. So street fashion followers who tuck their pants into their socks are safe. For supporters of the classic style, experts recommend using chemicals - sprays, which come in two types: repellents repel ticks, acaricides kill, they should only be used on clothes. If a tick has overcome all lines of defense and still bites, it is not necessary to take it to the doctor. Director of the Institute of Health Economics at the Higher School of Economics Larisa Popovich knows how to get the parasite on her own: “Pour oil over the tick and carefully, swinging it from the side, you need to pull it out. If you just pull, then the mandibles will remain in the wound, and they may just contain a transferable infection.”

How dangerous is a tick within the city?

However, this does not mean that everything will work out. If the tick turns out to be encephalitic, the victim will find out about it in a few days at best: it will all start with a fever and continue, if unlucky, with loss of coordination and even paralysis. Going through such an experience after being bitten by a Moscow tick until recently was exotic, until a focus of encephalitis was found in the Krylatsky Forest Park last year.

Vaccination can save you from it; the cost of vaccination is about 1.5 thousand rubles. in a paid clinic. Or you can insure against a tick bite for 250-500 rubles. The payment amount covers the cost of treatment and tests. But such a service is more relevant in Siberia, says Maxim Danilov, vice-president of the All-Russian Union of Insurers: “There are such products in Moscow, but here they are less popular than in regions where ticks are a real problem. Tick policies are really popular in a number of regions, they are cheap, and they are bought in tens of thousands. They still don’t make a significant contribution to the company’s revenue.”

What products do insurance companies offer?

But the tick is dangerous not so much because of encephalitis as due to unforeseen expenses - its examination and emergency treatment without insurance can cost, for example, 6.5 thousand rubles. - an amount disproportionately large for such a small parasite.

800 thousand Russians have already been vaccinated against tick-borne encephalitis this year, reports Rospotrebnadzor. In total, it is planned to vaccinate more than 3 million people.