When does the tick activity season begin and end

Despite the diversity of families, it is ixodid (Ixodidae) ticks that pose the greatest danger to humans and animals. Like all arthropods, the life of these parasites is cyclical and directly depends on many external factors, primarily climatic.

In our country, the tick activity season begins in early spring and ends in late autumn, but the greatest chance of becoming a victim of the parasite falls on special periods, during which the activity of ticks increases significantly - we'll talk more about this later ...

On a note

Ixodic ticks have a three-host type of development, and although they spend most of their lives outside the victim’s body, each of their life stages requires parasitism for the subsequent transition to a new form.Knowing the behavior of ticks during the period of food activity in different months of the year, one can avoid unwanted contact with the parasite and thus avoid the serious potential danger of its being bitten.

 

Stages of tick development: at what stage are these parasites the most active and dangerous for humans?

Ixodic mites throughout their development have several life forms. The very first stage of parasite development is an egg. Females lay their eggs in rotting forest flooring or dried grass compressed, and then die. One female is able to lay up to several thousand eggs.

Eggs develop over 30–40 days and do not pose a danger to people and animals. However, at this stage pathogens of infectious diseases can be transmitted from female to egg.

Under favorable temperature conditions, accelerated hatching of larvae occurs from eggs. The larvae are full-fledged parasites, and for further development they must necessarily find a host-host. However, at this stage, the tick larvae are practically not dangerous for humans, as they feed on the blood of small rodents or birds.

In most cases, the larvae do not find food for themselves during the first season and go into the winter, plunging into rotted leaves or making their way to the nests of birds. Overwintering tick larvae in the spring "wake up" and attack chicks that hatch in nests, or feed on the blood of small mammals.

The parasite feeds on for 2-3 days, after which it leaves the host and begins the transition to the next life form. Depending on the favorable climatic conditions, the transition to the next stage may be delayed. The peak of parasitic activity of the larvae occurs in autumn.

After molting, the larvae become nymphs. Nymphs of forest ticks are in many ways similar to an adult individual, both in shape and size.

Nymphs wintering in the burrows of mammals go through the entire development cycle much faster since they do not search for food. Individuals wintering in the forest litter, when establishing positive average daily temperatures, are activated and selected to the surface to search for the victim. In the middle zone of the nymph ticks are active from early spring to late autumn, but this form of the parasite is most dangerous from mid-spring to early summer.

At this stage of development, the parasite requires larger warm-blooded animals for parasitism, and hares, badgers, foxes and some domestic animals become its victims. In some cases, the person also becomes a victim.

On a note

Nymphs of ticks are no less dangerous to humans than adults, as they can be carriers of such pathogens as tick-borne encephalitis, Lyme borreliosis, tularemia, and several others.

After saturation, the parasites leave the host's body and climb into the shelters for a serious restructuring of their body and go into the adult stage - the imago. This process can take a long period, and its speed depends on the ambient temperature and the quality of the previous feed.

Thus, the entire development cycle of an Ixodes tick can take from one to four to five years, and is accompanied by a constant change of hosts. The greatest danger to humans is the final stage of development of the parasite - the adult individual.

 

Seasonal changes in tick activity

The activity of ixodic ticks has a pronounced dependence on the season (seasonality).In the central and more northern regions of Russia, where seasonal climatic fluctuations are most noticeable, special periods of slowing down of activity — diapause — are pronounced in the biological rhythms of the parasite.

There are two types of diapause:

• Morphogenetic;
• Behavioral.

Morphogenetic diapause is associated with the loss of activity of the primary life stages of ticks. Most often, it is expressed by slowing the process of hatching from larvae’s eggs and slowing down of molting in nymphs that are saturated with blood. This behavior allows the arthropod to synchronize their life rhythms with seasonal changes in temperature and humidity.

During morphogenetic diapause, ticks are inactive and not as dangerous for humans as in other periods.

It is important to know

Transmission of infectious agents from ticks to humans can occur not only at the time of physical contact or bite. There are frequent cases of tick-borne encephalitis infection from raw dairy products obtained from infected goats, sheep, and cows. In turn, infection of livestock is possible both when bitten by a tick, and when an infected parasite enters the body through the digestive system. Thus, there is a chance of infection even during diapause.

Behavioral diapause is inherent in adult ixodides, and is expressed in the reduction of aggression and loss of activity during the search for food. This type of diapause is associated with seasonal changes in ambient temperature and day length.

It is not uncommon for several climatic factors to be superimposed on one another and cause long-term behavioral diapause in forest ticks. Under such conditions, the season of ticks subsides rather quickly, and adult individuals go to wintering hungry.

During diapause, ticks do not pose a serious danger to humans, as they are in inactive state and do not hunt.

On a note

During the period of diapause, especially during wintering, resistance to the adverse effects of temperature and humidity increases many times in ticks.

In early spring, after the snow melted, there is a peak in the physiological activity of adults. During this period, domestic animals, such as hunting dogs, as well as small cattle, often suffer from tick bites.

The danger of infection with infectious diseases when in contact with ticks increases many times during the first warm spring days.This is due to the fact that long-term diapause is abruptly replaced by increased activity of ticks when a positive average daily temperature is established. Prolonged winter abstinence from food requires a large expenditure of vitality, so in spring the parasites turn on the mechanism of activation and increased aggression.

Launched in early spring, the mechanism of reactivation in ixodides causes them to hunt, even with incompletely descended snow cover. Domestic grazing animals, which came out in search of vegetation that appeared from under the snow, became victims of ticks during this period.

The second peak of tick activity is observed in early autumn, when average daily temperature and humidity indicators are most favorable for spending most of the time in guard mode. The largest number of tick bites is recorded at the end of summer and reaches a peak at the beginning of autumn, when the days are still quite warm, but there is already no sweltering heat and lack of moisture.

In the middle of summer, especially in dry seasons, the parasites are less aggressive, since in the upper grass layers there is too low humidity and strong exposure to sunlight.Hunting individuals are often forced to descend into the lower grass layers, where the microclimate is more favorable. In such conditions, the trapping type of hunting is ineffective, and most parasites are forced to reduce their search for prey.

 

Factors affecting the activity of the parasite

The most optimal conditions for the growth and development of Ixodes ticks are provided by a tropical climate. Tropical humidity and favorable temperature contribute to the rapid transition from one life form to another. In countries with a warm climate, the life cycle of the parasite can take place in one year or even less.

In Russia, in temperate and northern latitudes, Ixodes ticks develop over a longer period.

It is interesting

Natural and climatic factors, such as negative temperature or low humidity, not only impede the development of ticks, but also significantly increase the life of the parasite, sometimes several times.

An important role in the seasonal activity of forest ticks is played not only by temperature and humidity, but also by the ratio of day and night in daily cycles. Photoperiodic reactions are inherent in the vast majority of ixodic ticks.A change in the ratio of the longitude of day and night causes a response response in parasites, including a change in reproductive activity (mating season) and behavioral diapause.

In northern latitudes, with increased daytime during the summer period, Ixodes ticks exhibit completely different behavioral responses than individuals of the same species, but common in southern latitudes. Due to this, the fall of aggressiveness in the summer months does not occur, and the greatest peak of activity of encephalitic ticks in the northern regions of Russia falls in June-July.

As a rule, each locality has its own tick populations, ideally adapted to specific natural and climatic factors, and which have formed their established behavioral characteristics.

 

Tick ​​activity in different climatic zones

The same types of mites exhibit completely different forms of behavior in zones with different climates.

Thus, in central Russia, in a zone with a temperate climate, two jumps of seasonal activity of ixodid ticks are clearly pronounced in the spring and autumn periods. In adult individuals, activity peaks are replaced by behavioral diapauses — summer and winter.

In Moscow, the spring surge of aggressive behavior begins in early April and lasts until mid-June. The highest frequency of tick attacks on people is recorded in the first days of May, and lasts two weeks. In mid-June, the tick season moves into a lull due to summer behavioral diapause, and resumes in mid-August.

As a rule, the middle of October in Moscow and the neighboring territories falls on the beginning of the winter behavioral diapause in Ixodes ticks, and its end comes at the beginning of April.

In the southern regions of Russia (in the Volga region, in the Kuban), a surge in activity of parasites is observed in early spring and ends in late autumn. Summer diapause in hot regions is longer.

In those climatic zones where rain is rare and dry summer is often observed, ticks are forced most of the time to be near the roots of plants at the level of the soil - where there is a higher level of humidity. During these periods, the number of parasite attacks on humans and animals is significantly reduced. Seasons of tick activity in similar climatic zones last from March to May and from September to November.

In server latitudes in the Leningrad Region, in Karelia, in the Urals, in Siberia, and also in areas with an even colder climate, the summer diapause for ticks is short and sometimes absent (and may depend on the weather).

In St. Petersburg, the maximum recorded attacks on a person occur in the first and last weeks of the summer. And in the Arctic, the activity of parasitic individuals reaches its highest point in June and July.

During periods of high activity, ticks need to behave most carefully. To reduce the likelihood of becoming a victim of the parasite, you need to dress properly when going out into nature and take additional protective measures in advance.

 

The risk of infection with tick-borne encephalitis and borreliosis, depending on the season

Ixodes mites are specific carriers of pathogens of many vector-borne natural focal diseases that are dangerous to humans and domestic animals.

The most dangerous are tick-borne encephalitis and borreliosis. The causative agents of these diseases can be found in the body of the tick at all stages of its development - from the egg to the adult.

The most common carriers of dangerous diseases are taiga ticks - their degree of infection reaches 10-15% of the total population.

Human infection with tick-borne encephalitis can occur in two ways:

• Transmissible - by direct contact, bite or crush an infected parasite;
• Alimentary - by eating the milk of sick animals or dairy products that have not undergone heat treatment.

On a note

Goats and sheep can asymptomatically carry tick-borne encephalitis and be a source of increased danger to humans.

The probability of encephalitis in a person directly depends on the number of parasite populations in the area of ​​residence, the degree of their aggressiveness, as well as the size of the natural source of pathogens.

During periods of summer diapause, the chance of becoming a victim of an infected tick is significantly lower. However, grazing animals often swallow tick larvae along with grassy vegetation and become carriers of a dangerous disease themselves.

On the territory of Russia, Siberia, the Far East and Karelia are among the epidemic regions of tick-borne encephalitis. In the center of Russia, including in the Moscow region, the incidence of this disease is low. The map of tick-borne encephalitis is shown below:

Another, no less dangerous disease transmitted by ixodic ticks is borreliosis (Lyme disease). The distribution of this disease covers the entire territory of the Russian Federation, from Kaliningrad to Sakhalin. Borreliosis is registered in all regions of the country with a frequency of two to four cases per hundred thousand inhabitants.

The likelihood of tick-borne borreliosis is directly dependent on climatic factors and the number of tick populations on the ground.

It is important to know

Transmission of the causative agent of Lyme borreliosis to a person can occur not only when it is bitten, but also when the parasite is crushed while it is being removed from domestic animals (through damaged skin).

The most dangerous epidemic periods coincide with the periods of seasonal activity of ticks and have obvious marked jumps from April to June and from August to October.

In the hot period, ixodic ticks make daily migrations between grass tiers, therefore at night there is an increased likelihood of becoming a victim of the parasite. All ixodid ticks are active around the clock outside the diapause period.

Also a serious factor increasing the number of foci of the causative agent of borreliosis is the number of small vertebrates within the habitat of the parasite.In some climatic zones, the maintenance of natural reservoirs of Borrelia is provided exclusively by mice of voles and shrews. With a decrease in the number of these rodents, the number of registered diseases of tick-borne borreliosis among the local population significantly decreases.

The season of increased risk of infection with tick-borne infections, as a rule, directly depends on the activity of the parasite. And although a person is a random component of the parasitic system of Ixodes ticks, it is important to always remember about preventive safety measures, especially in those periods when the seasonal activity of the parasite reaches its maximum.

 

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