Natural focal infections. Vector-borne and natural focal diseases

3.1. Natural and climatic conditions, history of the creation and development of the Norilsk industrial region By volume of production of marketable products, as well as by diversified nature economic activity of the six enterprises that were part of the Russian

Most vector-borne diseases are associated with specific areas where wild animals carrying these diseases are common. Vectors and carriers of vector-borne diseases live among the animals inhabiting a given territory and are in complex relationships with each other and with environmental conditions. They are well adapted to their habitat. Natural foci of vector-borne diseases arose in the process of evolution and exist independently of humans. When entering the territory of a natural outbreak, a person can become infected with a vector-borne disease when bitten by vectors.

Vector-borne diseases with natural focality are characterized by the following features:

Circulate in nature independently of humans;

The reservoir is wild animals, which together with pathogens and vectors form a biocenotic complex;

Distributed in areas with a certain landscape, climate and biocenosis. Components of a natural hearth:

Pathogen;

Reservoir master;

Complex of natural conditions;

Presence of a vector, if transmissible.
An example of a vector-borne disease with natural focality would be tick-borne relapsing fever. Foci have been found in deserts and semi-deserts. Reservoir hosts are porcupines, gerbils, etc. Carriers are village ticks that live in burrows, caves, and abandoned dwellings. Feeding on the blood of reservoir animals, ticks maintain the outbreak for many years.

Transovarial transmission of the pathogen is possible, i.e. transmission through eggs from one generation to the next. From an infected egg, larvae, nymphs and adults develop, infected with spirochetes that cause tick-borne relapsing fever. This method of transmitting the pathogen allows it to be preserved long time. Ticks are not only carriers, but also reservoir hosts of the pathogen.

Transmissible diseases with natural focality include plague, leishmaniasis, tick-borne spring-summer encephalitis, etc.

Natural focal diseases include some helminthiases (diphyllobothriasis, opisthorchiasis, trichinosis, etc.).

The doctrine of natural focality has made it possible to develop measures for prevention and protection against these diseases. Prevention involves individual protection and destruction of reservoir animals.

Anthroponoses – diseases whose pathogens only affect humans. The biological host and source of pathogens is an infected person (dysenteric amoeba, lamblia, trichomonas, etc.).

Zoonoses – diseases whose pathogens affect the human and animal body. The source of pathogens is domestic and wild animals (Leishmania, Balantidia, etc.).

· PROTOZOOLOGY,

· helminthology,

· Arachnoentomology.

The body of protozoa consists of a shell, cytoplasm, nucleus, and various organelles that provide the functions of nutrition, movement, and excretion. Protozoa move with the help of pseudopodia (sarcodaceae), flagella and undulating membranes (flagellates), and cilia (ciliate ciliates).

The food for unicellular organisms is organic particles, including living microorganisms, as well as nutrients dissolved in the environment. Some ingest food particles through a cellular mouth, others absorb food particles using pseudopodia (pseudopodiums) formed in any part of the body. In this case, the particle flows around and ends up inside a vacuole in the cytoplasm of the protozoan, where it is digested (pinocytosis). In some species of protozoa, nutrition occurs by absorption of nutritious juices and dissolved nutrients body surface (endosmotically).

Protozoa of some species are capable of encysting, that is, they are rounded and covered with a dense shell (for example, dysenteric amoeba). Cysts are more resistant to adverse effects external factors than vegetative forms. When hitting favorable conditions The protozoa emerge from the cyst and begin to reproduce.

The protozoa that live in the human body belong to the kingdom Animalia, sub-kingdom Protozoa. In the subkingdom of Protozoa ( Protozoa) There are three types: Sarcomastigophora,Apicomplexa And Ciliophora, having medical significance ( see table).

NATURAL FOCALITY OF DISEASES- a feature of some infectious human diseases, which consists in the fact that they have evolutionary foci in nature, the existence of which is ensured by the sequential transition of the causative agent of such a disease from one animal to another; In transmissible natural focal diseases, pathogens are transmitted by blood-sucking arthropods (ticks, insects).

Naturally focal are many viral, bacterial, protozoal diseases, helminthiases and some mycoses related to zoonoses (see). The most common and studied are tick-borne and Japanese encephalitis (see Tick-borne encephalitis, Mosquito encephalitis), hemorrhagic fevers (see), lymphocytic choriomeningitis (see), psittacosis (see), rabies (see), yellow fever (see) , some rickettsioses (see), tularemia (see), plague (see), brucellosis (see), erysipeloid (see), listeriosis (see), leptospirosis (see), tick-borne spirochetosis (see) , leishmaniasis (see), toxoplasmosis (see), opisthorchiasis (see), diphyllobothriasis (see), schistosomiasis (see), etc. Natural focal diseases are divided into vector-borne (in the presence of a carrier of the pathogen), subdivided into obligately transmissible and facultatively transmissible, and non-transmissible (transmitted without the participation of a carrier). Carriers (see), as a rule, are arthropods, carriers of the pathogen are vertebrates. Natural focal diseases are characterized by pronounced seasonality: diseases are associated with a person’s stay in certain places of a particular geographical landscape during the corresponding seasons of the year.

The presence of the pathogen in the body of vertebrate animals in some cases leads to disease, in others the animals remain asymptomatic carriers. The causative agent of the disease in the body of a specific carrier does certain part his life cycle: multiplies, reaches an infective (invading) state and takes the position of exit from the vector. This process takes place in the body of an invertebrate animal (vector) that does not have constant temperature body, and depends on temperature and its fluctuations in the environment. The microorganism and its carrier can be in a symbiotic relationship (see Symbiosis). In such cases, the pathogen finds a favorable habitat in the carrier’s body and at the same time does not have a noticeable effect. adverse influence on its development, life and reproduction. Moreover, the pathogen adapts to the reproduction process of its carrier and, circulating in its body, sometimes penetrates the egg cells. From the infected eggs laid by the female carrier, daughters infected with the pathogen emerge, which, at the first sucking of the blood of susceptible animals, transmit the pathogen to them. The same may happen with the subsequent population. This is how transovarial transmission (see) of the pathogen occurs from an infected carrier to its descending generations. For the causative agent of tick-borne encephalitis, this was traced over two generations of the carrier, which may not be the limit. In other species ratios of the carrier and the microorganism, the latter has a certain patol. effect on the carrier’s body, which can shorten its life.

Interspecific relationships between components of biocenoses natural foci diseases developed in the process of evolution of microorganisms, animals - donors and recipients, as well as carriers in certain conditions of the emerging environment, regardless of the existence of humans, and for some diseases, perhaps even before the appearance of the species Homo primigenius and Homo sapiens on the ground.

Thus, the natural focus of a human infectious disease is a section of the territory of a certain geographical landscape, in which certain interspecific relationships have evolved evolutionarily between the causative agent of the disease, animals - donors and recipients of the pathogen, and in case of vector-borne diseases - and its carriers in the presence of environmental factors , conducive to the circulation of the pathogen.

Natural foci of diseases are territorially associated with certain areas of the geographic landscape, that is, with its biotopes (see Biotope). In turn, each biotope is characterized by a certain biocenosis (see). The combination of a biotope and a biocenosis is a biogeocenosis (see). The nature of the biotopes is very diverse. In some cases it is clearly limited, for example. a rodent burrow with its various inhabitants in a hot desert zone. Such a biotope can be a natural focus of not one, but two or three different diseases: for example. The burrow of gerbils Rhombomys opimus is a natural site of tick-borne spirochetosis, zoonotic cutaneous leishmaniasis and some bacterial diseases. In other cases, the boundaries of the territory of natural foci of the disease are diffuse and therefore less defined in outline. Thus, the litter of broad-leaved taiga is a very favorable place for the tick Ixodes persulcatus, a specific carrier of the causative agent of tick-borne encephalitis, to stay outside the host. However, even over its vast area, these ticks are scattered unevenly, some places are free from them, while in others they accumulate in significant quantities, which happens on the paths of animals moving towards a watering hole.

Infected vectors in natural foci of the disease behave differently towards recipients, including humans; These differences are related to the method of movement and the search for “prey” for feeding. Flying carriers (mosquitoes, mosquitoes, etc.) can cover considerable distances, looking for suitable food items. For example, in the Karakum desert, phlebotomuses, which hatch in the burrows of gerbils and other rodents, fly out at night and, in search of food, can move away from their burrow to a distance of up to 1.5 km and attack people in the process. Crawling arthropods, e.g. ticks are not prone to distant migrations; they crawl not far from the place where they hatch from the eggs or from the place of molting. Climbing onto grass, low bushes or dead wood exposed after the snow melts, they take a lurking pose and remain in place until they cling to a passing animal or person, after which they begin the act of blood sucking.

Natural foci of diseases exist due to the continuously occurring transmission of the pathogen from the body of one animal to the body of another. Such foci can remain unknown to a person for centuries until he enters their territory, but even then a person’s disease occurs only with a combination following conditions: the natural focus of a vector-borne disease must be located in valence state, that is, in the outbreak area there must be hungry carriers infected with the pathogen, ready to attack the emerging people as a tempting source of abundant food; people entering the territory of a natural outbreak must be non-immune to this disease; carriers must introduce into the human body a dose of the causative agent of the disease sufficient for its development; the pathogen itself must be in a virulent state.

Apparently, cases of introducing small doses of the pathogen into the body, which are insufficient for the development of the disease in an infected person, are practically more frequent. However, this process does not go unnoticed for the recipient; in his body, antibodies to the introduced pathogen are produced, and the person becomes immune to the action of new doses of the pathogen, sufficient in normal conditions for the full development of the disease. In this case, the carrier of the pathogen may have positive influence on the human body, leading it to a state of immunity to the pathogen of the corresponding type. The presence of antibodies to pathogens of some natural focal diseases, for example. tick-borne and mosquito encephalitis has also been found in animals that do not suffer from these diseases, which is associated with their prolonged stay in the territory of the natural focus. Detection of antibodies in people and animals in certain areas is important diagnostic method detection of hidden natural foci of relevant diseases.

To characterize natural foci of diseases, it is important to know the conditions for the persistence of their existence and to have a clear understanding of the possibility of their movement. Both of these issues are closely related to each other. It is known, for example, that natural foci of tick-borne encephalitis and some tick-borne rickettsioses can exist only in certain natural conditions, since ixodid ticks, carriers of the pathogens of these diseases, cannot, as a rule, live and reproduce close to humans, much less stay in his home. It is, of course, possible that single infected ticks may be brought into a person's home, which can lead to sporadic diseases, but this is an exception. At the same time, carriers and carriers of pathogens of natural focal diseases can suitable conditions move to new habitats, which significantly changes the epidemiology of the corresponding disease. As a result of such movements, carriers of pathogens of natural focal diseases can move into housing or end up in the immediate environment of a person. In this case, intra-household diseases of people arise (for example, tick-borne relapsing fever, cutaneous leishmaniasis, plague and certain other diseases). Thus, Ornitllodoros papillipes ticks - carriers of spirochetes - the causative agents of tick-borne relapsing fever - can settle in the burrows of Turkestan rats located in housing, forming a kind of burrow biocenosis with house rodents. Such foci of infectious diseases, associated in their origin and maintenance of existence with some form of human activity, are called anthropourgic.

No matter how the natural foci of diseases undergo modifications, their primary connection with geographic landscapes does not lose its fundamental significance even when the causative agent of the disease is transmitted by many types of vectors and, in addition, by various non-transmissible methods (for example, tularemia). And in this case, biotic factors are still identified that determine the durable existence of foci of such diseases in natural areas, even those used by humans.

The connection of natural foci of diseases with certain geographical landscapes makes it possible to provide a provisional assessment of possible epidemics. dangers of the territory and carry out preventive measures in advance to protect people’s health when it is not possible to examine the area for the presence of natural foci of diseases or, at least, carriers of pathogens. Landscape epidemiology of such diseases is closely related to regional pathology, but regional pathology extends only to certain large administrative parts of the state, while landscape epidemiology focuses on areas of various landscapes, which often extend over several large administrative parts of the country. Determining the territorial distribution of natural foci of diseases becomes especially important, for it is the basis of nosogeography (see) of the corresponding diseases. The doctrine of P. o. human diseases is the key to studying new diseases.

E. N. Pavlovsky.

Natural focal diseases are infectious diseases that exist in natural foci due to persistent foci of infection and invasion maintained by wild animals. The doctrine of natural focal disease was developed by E. N. Pavlovsky (1938) and his school.

They are characterized by following signs: 1) pathogens circulate in nature from one animal to another, regardless of humans; 2) wild animals serve as the reservoir of the pathogen; 3) diseases are not distributed everywhere, but in a limited area with a certain landscape, climatic factors and biogeocenoses.

The components of a natural outbreak are: 1) pathogen; 2) animals susceptible to the pathogen - reservoirs: 3) the corresponding complex of natural and climatic conditions in which this biogeocenosis exists. A special group of natural focal diseases consists of vector-borne diseases, such as leishmaniasis, trypanosomiasis, tick-borne encephalitis, etc. A characteristic epidemiological feature of diseases with natural focality is the strictly expressed seasonality of diseases, which is due to the biology of animals - keepers of infection in nature or carriers.

Vector-borne diseases can be anthroponoses, anthropozoonoses and zoonoses. Anthroponoses include malaria (only humans are affected), anthropozoonoses include leishmaniasis, taiga encephalitis, trypanosomiasis (humans and vertebrates are affected), and zoonoses include avian malaria (only animals are affected).

Answer

Vector-borne diseases (Latin transmissio - transfer to others) are infectious diseases transmitted by blood-sucking insects and representatives of the phylum arthropods.

About two hundred official diseases are known that have a vector-borne transmission route. They can be caused by various infectious agents: bacteria and viruses, protozoa and rickettsia, and even helminths.

Obligately vector-borne diseases are transmitted from infected animals to healthy ones exclusively by specific carriers. Obligately transmissible diseases include malaria, leishmaniasis, etc.

Facultatively vector-borne diseases are transmitted both through vectors and through food and water as a result of contact with an infected animal. These include various intestinal infections, anthrax, tularemia.

Vectors

There are mechanical and specific carriers.

The pathogen passes through a mechanical carrier in transit (without development or reproduction). It can persist for some time on the proboscis, body surface or in digestive tract arthropod animal.

Answer

Biological;

Immunological;

Environmental;

Public.

Prevention methods include:

Ecological - these methods involve the prevention of anthropogenic pollution of freshwater bodies.

Social - aimed at observing the rules of personal and public hygiene.