From Big Medical Encyclopedia

NATURAL OChAGOVOST of diseases — the feature of some infectious diseases of the person consisting that they have evolutionarily arisen centers which existence is provided with consecutive transition of the causative agent of such disease from one animal to another in the nature; at transmissible natural and focal diseases activators are transferred by blood-sicking arthropods (mites, insects).

Many viral, bacterial, protozoan diseases, helminthoses and some mycoses relating to are natural and focal zoonosis (see). Tick-borne and Japanese encephalitis is most widespread and studied (see. tick-borne Encephalitis , Encephalitis mosquito ), hemorrhagic fevers (see), choriomeningitis lymphocytic (see), ornithoses (see), rage (see), yellow fever (see), some rickettsioses (see), tularemia (see), plague (see), brucellosis (see), erizipeloid (see), listeriosis (see), hay fever (see), tick-borne spirochetosis (see), leyshmanioza (see), toxoplasmosis (see), opisthorchosis (see), diphyllobotriases (see), schistosomatosis (see), etc. Natural and focal diseases share on transmissible (in the presence of a carrier of a disease-producing factor), subdivided on obligate and transmissible and optional and transmissible, and not transmissible (transferred without participation of a carrier). Carriers (see) arthropods, carriers of the activator — vertebrate animals, as a rule, are. Natural and focal diseases are characterized by the expressed seasonality: are connected by zabolevaniyay with stay of the person during the corresponding seasons of year in certain places of this or that geographical landscape.

Finding of a disease-producing factor in an organism of vertebrate animals in one cases leads to a disease, in others — animals remain asymptomatic carriers. The disease-producing factor in an organism of a specific carrier makes a certain part of the life cycle: breeds, reaches the infecting (infesting) state and takes a position of escaping of a carrier. This process proceeds in an organism of the backboneless animal (carrier) which does not have constant body temperature and depends on temperature and its fluctuations in the environment. The microorganism and its carrier can be in symbiotic ratios (see. Symbiosis ). In such cases the activator finds the favorable habitat in an organism of a carrier and at the same time does not exert noticeable adverse impact on its development, life and reproduction. Moreover, the activator adapts to process of reproduction of the carrier and, circulating in its organism, sometimes gets into egg cells. The infected eggs laid by a female of a carrier leave the affiliated individuals infected with the activator who at the first suction of blood of susceptible animals transfer to them a disease-producing factor. The same can be also with the subsequent population. So occurs transovarial transfer (see) disease-producing factor from the infected carrier to its descending generations. For the causative agent of tick-borne encephalitis it is tracked on two generations of a carrier that, perhaps, is not a limit. In other specific ratios of a carrier and a microorganism the last renders a nek-swarm patol. action on an organism of a carrier that can shorten his life.

Trans-species relationship of components of biocenoses of the natural centers of diseases developed in the course of evolution of microorganisms, animals — donors and recipients, and also carriers in certain conditions of the forming environment regardless of existence of the person, and for some diseases, perhaps, and before emergence of types of Homo primigenius and Homo sapiens on Earth.

Thus, the natural center of an infectious disease of the person — the site of the territory of a certain geographical landscape, on Krom evolutionarily there was certain trans-species relationship between a disease-producing factor, animals — donors and recipients of the activator, and at transmissible diseases — and its carriers in the presence of the environmental factors favoring to circulation of the activator.

The natural centers of diseases are territorially connected with certain sites of a geographical landscape, i.e. with its biotopes (see. Biotope ). In turn, certain is inherent to each biotope biocenosis (see). Set of a biotope and biocenosis is biogeocenosis (see). Character of biotopes is very various. In one cases there is accurately limited, e.g. a hole of a rodent to its various inhabitants in a zone of the hot desert. Such biotope can be the natural center not of one, but two or three different diseases: e.g. a hole of sandworts of Rhombomys opimus — the natural center of a tick-borne spirochetosis, a zoonotic skin leushmaniosis and some bacterial diseases. In other cases of border of the territory of natural focuses of the disease happen diffusion and therefore less certain on outlines. So, the laying of a broad-leaved taiga is very favorable place of stay out of the owner of a tick of Ixodes persulcatus — a specific carrier of the causative agent of tick-borne encephalitis. However and on its extensive square these mites are disseminated unevenly, one places are free from them, on others they crowd in significant amounts that happens on tracks of advance of animals to a watering place.

The infected carriers in natural focuses of the disease variously behave in relation to recipients, including also the person; these distinctions are connected with way of movement and search of «production» for food. The flying carriers (mosquitoes, mosquitoes, etc.) can overcome considerable distances, searching for suitable objects of food. E.g., in Kara Kum flebotomusa, vyplazhivayushchiyesya in holes of sandworts and other rodents, take off at night and in search of an object of food can move away from the hole on distance to 1,5 km and attack at the same time people. The creeping arthropods, e.g. mites, are not inclined to the remote migrations; they nearby crawl away from the place of escaping of eggs or from the place of a molt. Climbing up a grass, undersized bushes or the dead wood bared after thawing of snow, they accept the trapping pose and remain on site, yet will not cling to the animal passing by or the person then start the act of a krovososaniye.

The natural centers of diseases exist thanks to continuously happening transfer of a disease-producing factor from an organism of one animal in an organism of another. Such centers can remain centuries unknown to the person while it does not get on their territory, but also then the disease of the person occurs only at a combination of the following conditions: the natural center of a transmissible disease shall be in valence state, i.e. in the territory of the center there have to be hungry, infected with a disease-producing factor carriers ready to attack the appeared people as on a tempting source of rich food; the people who entered on the territory of the natural center shall be not immune to this disease; carriers shall enter the dose of a disease-producing factor sufficient for its development into a human body; the disease-producing factor shall be in a virulent state.

Apparently, cases of introduction to an organism of small doses of the activator which are insufficient for a course of a disease at the infected person are almost more frequent. However this process does not take place completely for the recipient; in its organism there is a development of antibodies to the entered activator, and the person becomes unreceptive to action of the new doses of the activator sufficient in usual conditions for a full course of a disease. In this case the carrier of a disease-producing factor can exert positive impact on a human body, bringing it to a state of immunity to a disease-producing factor of the corresponding look. Existence of antibodies to causative agents of some natural and focal diseases, e.g. tick-borne and mosquito encephalitis, is established also at animals who have no these diseases that is connected with their long stay in the territory of the natural center. Identification of antibodies at people and animals in certain territories is an important diagnostic method of detection of the hidden natural centers of the corresponding diseases.

For the characteristic of the natural centers of diseases it is important to know conditions of firmness of their existence and to have clear idea of a possibility of their movement. Both of these questions are closely connected with each other. It is known, e.g., that the natural centers of a tick-borne encephalitis and some tick-borne rickettsioses can exist only in a certain environment since ixodic ticks — carriers of causative agents of these diseases cannot live and breed, as a rule, closely to the person and the more so to stay in his housing. Cases of a drift of the single infected mites in housing of the person are possible, of course, that can lead to sporadic diseases, but it is an exception. At the same time carriers and carriers of causative agents of natural and focal diseases can under suitable conditions move in new habitals that significantly alters epidemiology of the corresponding disease. As a result of such movements carriers of causative agents of natural and focal diseases can move to housing or appear in a direct environment of the person. At the same time there are intra house diseases of people (e.g., a tick-borne typhinia, a skin leushmaniosis, plague and nek-ry other diseases). So, ticks of Ornitllodoros papillipes — carriers of spirochetes — activators of a tick-borne typhinia — can settle in holes of the Turkestan rats who are in housing, forming some kind of norovy biocenosis with house rodents. Such centers of infectious diseases connected in the origin and maintenance of existence with any form of activity of the person are called antropourgichesky.

To what modifications the natural centers of diseases, primary communication them with geographical landscapes would not be exposed does not lose the basic value even then when the disease-producing factor is transferred by many types of carriers and, besides, various not transmissible ways (e.g., a tularemia). And in this case nevertheless the biotic factors defining strong existence of the centers of such diseases in natural territories, even used by the person come to light.

The Ekologo-parazitologichesky analysis of living conditions of the natural centers of diseases is important in system development anti-epidemic actions (see) on full eradication of these centers in certain territories, and also on individual and mass protection of people from attack of carriers during their stay in a zone of the operating centers of diseases. On the majority of the natural centers of diseases essential impact is made by activity of the person. In one cases it suppresses the centers, in others causes reorganization of their biocenotic structure, and the center remains in an active state.

Communication of the natural centers of diseases with certain geographical landscapes allows to give provisional to a honey agaric possible epidemich. dangers of the territory and in advance to hold safety events for health protection of people, when there is no an opportunity to inspect the area on existence in it of the natural centers of diseases or, at least, carriers of causative agents of diseases. The landscape epidemiology of such diseases is closely connected with regional pathology, but regional pathology extends only to separate large administrative parts of the state while the landscape epidemiology focuses attention on territories of various landscapes which often stretch for several large administrative parts of the country. Definition of territorial distribution of the natural centers of diseases becomes especially particularly important because it is a basis nozogeografiya (see) corresponding diseases. The doctrine about P. of the lake of diseases of the person — a key in studying of new diseases.

See also Transmissible diseases .

Bibliography: Kucheruk V. V. Mammals — carriers of the diseases dangerous to the person, in book: Usp. sovr. teriologiya, under the editorship of V. E. Sokolov, page 75, M., 1977; Pavlovsky E. N. About a natural ochagovost of infectious and parasitic diseases, Vestn. Academy of Sciences of the USSR, L' «10, page 98, 1939; it e, Guide to parasitology of the person, t. 2, M. — L., 1948; The Natural ochagovost of diseases of the person and regional epidemiology, under the editorship of E. N. Pavlovsky, etc., L., 1955.

E. N. Pavlovsky.