Naturally focal vector-borne infectious diseases. Natural focal infections

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

Having developed the doctrine of the natural focality of vector-borne diseases of humans and farm animals, he laid the foundations of medical and veterinary biogeography. According to the doctrine of the natural focality of vector-borne diseases, the peculiarity of some diseases is that their pathogens, specific carriers and animals (pathogen reservoirs) for a long time exist in natural conditions (foci) regardless of human habitation. A person becomes infected with pathogens of wild animals by entering temporarily or living permanently in the territory of a natural outbreak. Characteristic Such diseases are the presence of natural reservoirs (foci) of pathogens among wild mammals (mainly rodents) and birds. The most pronounced natural focality of vector-borne diseases is in which the spread of infection occurs through blood-sucking arthropods, when the causative agent of the disease circulates along the chain: animal - carrier - animal. Natural foci of vector-borne diseases are confined mainly to the junctions various types landscapes where it is observed greatest number rodents, birds and arthropod vectors; Certain diseases are characterized by certain landscapes: meadows (leptospirosis), steppes (Q fever), savannas (trypanosomiasis), etc. This location makes it possible to predict the possibility of the emergence of vector-borne diseases and organize preventive measures accordingly.

The founder of the doctrine of P. o. human diseases is E.N. Pavlovsky. It gained worldwide fame and recognition. In the Soviet Union, numerous students and followers of E.N. Pavlovsky studied the natural focality of many infectious human diseases.

The existence of natural foci of diseases is due to the continuous circulation of their pathogens among vertebrate animals - most often rodents, birds, as well as ungulates, predators, etc. (sources of infectious agents). The transmission of pathogens from animal to animal, as well as from animal to person, occurs mainly through insects and ticks (carriers of pathogens), however, other routes and factors for the transfer of pathogens are also possible, for example through water, food, contact, etc.

People or pets can become infected naturally focal diseases when entering the territory of a natural outbreak. Infection of people is also possible from domestic animals infected with a natural focal disease.

Natural focal diseases of people include the following vector-borne infectious diseases: dengue, yellow fever, mosquito encephalitis (see Mosquito encephalitis), Saint Louis encephalitis (see Encephalitis), equine encephalomyelitis, plague, visceral and cutaneous leishmaniasis, phlebotomy fever, sleeping sickness, Chagas disease, tick-borne encephalitis(see Tick-borne encephalitis), many tick-borne rickettsioses, hemorrhagic fevers, tularemia, tick-borne relapsing fever, Lyme disease.

There are natural foci of rabies, leptospirosis, lobothriasis, paragonimiasis, trichoinosis, schistosomiasis, echinococcosis, etc.

People who enter the territory of a natural outbreak can only get sick if the conditions are present. In the outbreak there must be carriers of pathogens in an active state. Transmission of the pathogen can only occur under certain environmental conditions, which mainly depends on the time of day, climate, landscape features, etc. Thus, most arthropod vectors are active in the warm season, ixodid ticks (carriers of the tick-borne encephalitis virus) are active mainly in the evening , mosquitoes (carriers of the mosquito encephalitis virus) - in the summer-autumn period; reproduction of the mosquito encephalitis virus occurs at temperatures not lower than 21°, infection with it is observed in Southern Primorye in most cases after a hot summer; It is possible to become infected with the plague from marmots only in the warm season, because... In winter, marmots hibernate and stay in a deep hole.

The most susceptible to many natural focal diseases are people who arrived to the focal point from outside, which is taken into account when determining who is subject to immunization.

The most effective measures to prevent natural focal diseases in people are immunization, as well as the use of repellents, wearing protective clothing, using protective nets, disinfestation and deratization in natural outbreaks. Great importance has sanitary educational work - explaining the need for personal preventive measures to protect against pathogens of certain natural focal diseases during the season of possible infection, especially among persons arriving at the outbreak from outside.

Bibliography: Kucheruk V.K. Mammals are carriers of diseases dangerous to humans, in the book: Usp. modern Theriology, ed. V.E. Sokolova, s. 75, M., 1977; Pavlovsky E.N. Natural focality of vector-borne diseases in connection with landscape epidemiology of zooanthroponoses, M. - L., 1964.

Theory of natural focality of infectious diseases

In 1889 D.K. Zabolotny suggested that different kinds Rodents in nature represent the environment in which plague bacteria persist. Later D.K. Zabolotny (1911) and his students (I.A. Deminsky, 1912, etc.) proved that the keepers of plague pathogens in nature are rodents - marmots, gophers, tarabagans, gerbils, rats, etc.

Since 1938, as a result of numerous studies by academician. E.N. Pavlovsky and collaborators on the etiology and epidemiology of tick-borne encephalitis, endemic rickettsiosis, leishmaniasis, tularemia and other infections developed a coherent doctrine of the natural focality of some vector-borne diseases.

A characteristic feature of this group of diseases is the existence of a natural reservoir of pathogens among wild animals and birds, among which epizootics occur.

The spread of these diseases among the animal world and from animals to humans occurs with the participation of blood-sucking insects and ticks. Thus, the causative agents of these infections continuously circulate in nature along the chain: animal-carrier-animal, and under certain conditions a person is included in the epidemic chain.

So, natural foci of infectious diseases arise and exist for a long time independently of humans as a result of evolutionarily established interspecific relationships between the pathogenic pathogen, the animal body and specific carriers living in certain natural biotopes, i.e. in certain climatic and geographical conditions, with certain flora and fauna.

Infection of a person susceptible to this infection occurs accidentally and this is due to his presence in the territory of a natural outbreak during the period of activity of vectors against the background of an emerging epizootic among animals.

So, the existence of a focus is ensured by the presence in it of a pathogen of a susceptible animal and the conditions for their infection (carrier, etc.).

Bloodsucking vectors include ticks, mosquitoes, fleas, lice, etc. Those diseases that are transmitted through vectors are called vector-borne. Thus, for the existence of a focus of a vector-borne infection, three components or a “focal triad” are required: the pathogen, the vector and the warm-blooded host. Transmissible diseases are tick-borne and mosquito-borne (Japanese, etc.) encephalitis, hemorrhagic fevers, tick-borne typhus of North Asia and tsutsugamushi fever and many others. Currently, another group of natural focal diseases is known, the transmission of the infectious principle in which occurs without the participation of a carrier (by contact) during cutting of carcasses, skinning and (or) during an attack and bite of the host animal (rabies, sodoku, etc.) , alimentary through water - anicteric leptospirosis or by airborne droplets etc. Some cases of infection with tick-borne encephalitis occur when consuming milk from sick (infected) goats, cows; plague, ornithosis, hemorrhagic fevers with renal syndrome and etc.

IN last years so-called anthropurgic (man-made) foci appeared as members of natural foci in territories developed by man within cities, villages and other human settlements (Q fever, yellow fever, Japanese mosquito encephalitis, etc.). This is due to the fact that many mosquitoes feed on humans and domestic animals, then find places where larvae breed in populated areas in various natural and artificial reservoirs, in the basements of houses, in various household utensils, in barrels of water and other places, thus becoming Thus, in synanthropes. Then they suck the blood of domestic animals and rodents infected with pathogens and, attacking a person, infect him.

Outbreaks with hungry infected vectors (ticks - tick-borne encephalitis, tularemia, endemic Lyme borreliosis, etc.) capable of infecting humans and animals are called valence.

Those natural foci in which pathogens of various infectious diseases circulate (tick-borne encephalitis and Lyme disease, plague, tick-borne rickettsiosis and tularemia, etc.) are called conjugate, etiological.

Natural foci are called multivector, in which there are several types of vectors, as in tularemia, endemic rickettsioses (mosquitoes, ticks, horseflies, fly flies, etc.), and if there is only one vector - monovector (mosquito fever).

If in natural foci there is only one type of donor animal, then they are called monohostal, and if there are several donor animals, then such foci are polyhostal, multi-host.

A characteristic epidemiological feature of diseases with natural focality is seasonality, which is determined by the biology of animals - guardians of the infectious principle in natural biotopes (hibernation - in the case of plague) or the activity of carriers. The second epidemiological feature of these diseases is their connection with a certain territory, with certain climatic and geographical conditions (enzootic, endemic). Natural focal infections are characterized by a fan-shaped type of transmission of pathogens. This means that many people become infected at the same time from one donor animal, which most often represents a biological dead end for the pathogen.

Influence natural conditions is also expressed in the second link of the epidemic process - the factors of transmission of infection.

The natural factor is of particular importance in cases where the carriers are ticks and other arthropods; in addition, the role of the factor in the number of vectors in the development of natural focal infections has long been known; the fewer carriers, the lower the incidence, up to elimination. The role of climatic factor on the development of pathogens in the carrier’s body (temperature) is also known. The great importance of natural processes is also noted in some other infections, the factors of transmission of the infectious principle in which are objects of inanimate nature (water of open reservoirs, contaminated wastewater, self-purification processes occurring in water, soil, their intensity, etc.). By promoting the rapid development and acceleration of these processes, we help reduce and eliminate gastrointestinal and other infections.

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

They are characterized by the following features: 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. Special group natural focal diseases constitute 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.

Natural focal diseases are infectious diseases that exist in natural foci due to persistent foci of infection and invasion maintained by wild animals. These include: tick-borne and mosquito (Japanese) encephalitis, tick-borne rickettsiosis (typhoid fever), various forms of tick-borne relapsing fever, tularemia, plague, hemorrhagic fever, African trypanosomiasis, diphyllobothriasis, opisthorchiasis and other pathogens, carriers, animal donors and recipients - - more or less permanent members of biocenoses of a certain geographical landscape. The doctrine of natural focal diseases was developed by E. N. Pavlovsky (1938) and his school.

Plague is an acute natural focal transmissible infection characterized by severe intoxication, high fever, lymphadenitis of bubonic type. Natural foci of plague located on the territory of Russia include: Central Caucasus, Terek-Sunzhensky, Dagestan plain-foothill and high-mountain, Caspian northwestern, Volga-Ural steppe and sandy, Tuva, Transbaikal, Gorno-Altai.

In Transbaikalia, the outbreaks are Borzinsky, Transbaikalsky, Ononsky, and Krasnokamensky districts. The carriers of the pathogen (Yersinia pestis) are: tarbagan, Daurian ground squirrel, birds of prey and fleas.

Tick-borne encephalitis - naturally focal transmissible (transmitted by ticks) viral infection, characterized by predominant damage to the central nervous system.

The main reservoir and carrier of the virus in nature are ixodid ticks. Rodents and other animals are additional reservoirs of the virus. The disease is characterized by strict spring-summer seasonality associated with the activity of ticks. Most cases of infection in Transbaikalia are observed in the South.

Leptospirosis - acute infectious disease, caused by a pathogen from the genus Leptospira. It is characterized by damage to the capillaries, often damage to the liver, kidneys, muscles, symptoms of intoxication, and is accompanied by undulating fever. Carriers: domestic animals (pigs), rodents, synanthropic animal species.

anthrax(malignant carbuncle, anthrax) is a particularly dangerous infectious disease of agricultural and wild animals of all types, as well as humans. The disease occurs with lightning speed, acutely or hyperacutely. Characterized by intoxication, the development of serous-hemorrhagic inflammation of the skin, lymph nodes And internal organs; occurs in the skin or septic form. The source of infection is sick farm animals: large cattle, horses, donkeys, sheep, goats, deer, camels, in which the disease occurs in a generalized form. Pets - cats, dogs - are slightly susceptible. In Transbaikalia, the foci are: Chita, Baleysky, Shilopuginsky, Borzinsky and Mogoituysky districts.

Tularemia is an acute infectious disease of animals and humans; caused by the bacterium Francisella tularensis. Named after the area of ​​Tulare in California, where it was first isolated from diseased ground squirrels. In addition to the USA, tularemia has been found in Russia, Canada, Japan, Sweden, Norway, France and other countries. Northern Hemisphere. It is transmitted to humans from sick or dead rodents and hares through direct contact with them or through water, straw, food contaminated by them, as well as by insects and ticks through bites. The pathogen enters the human body through the skin, mucous membranes of the eye, digestive organs and respiratory tract. In Transbaikalia, the foci are: Borzinsky, Transbaikalsky, Krasnokamensky, Ononsky, Nerchinsky, Olovyaninsky and A-Zavodsky districts.

Cholera - acute illness, resulting from rapid reproduction in the lumen small intestine cholera vibrio. Characterized by the development of massive diarrhea with rapid loss of extracellular fluid and electrolytes, the appearance of severe cases hypovolemic shock and acute renal failure. Refers to quarantine infections, capable of epidemic spread. The only source of Vibrio cholerae is humans. Reservoirs used for recreational and domestic purposes pose a risk of contamination.

Components of a natural hearth 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. Therefore, an obligatory component of a natural hearth vector-borne disease is also the presence carrier. The structure of such a focus is shown in Fig. 18.8.

1 - causative agent of the disease - leishmania, 2 - natural reservoir - Mongolian gerbils, 3 - the carrier of the pathogen is the mosquito, 4 - rodent burrows in semi-deserts Central Asia, 5 - the causative agent of the disease is the broad tapeworm, 6 - natural reservoir - fish-eating mammals, 7 - intermediate hosts - cyclops and fish, 8 - large freshwater bodies of Northern Eurasia

The category of diseases with natural focality was identified by Academician. E.N. Pavlovsky in 1939 based on expeditionary, laboratory and experimental work. Currently, natural focal diseases are being actively studied in most countries of the world. The development of new, uninhabited or sparsely populated territories leads to the discovery of new, previously unknown natural focal diseases.

Rice. 18.9. Mite Amblyomma sp.

Some natural focal diseases are characterized endemism, those. occurrence in strictly limited areas. This is due to the fact that the causative agents of the corresponding diseases, their intermediate hosts, animal reservoirs or vectors are found only in certain biogeocenoses. Thus, only in certain areas of Japan are four species of pulmonary flukes from the river settled. Paragonimus(see section 20.1.1.3). Their dispersal is hampered by their narrow specificity in relation to intermediate hosts, which live only in some water bodies in Japan, and the natural reservoir is such endemic animal species as the Japanese meadow mouse or Japanese marten.

Viruses of some forms hemorrhagic fever are found only in certain areas of East Africa, because this is where the habitat of their specific carriers is located - ticks from the river. AtYuotta(Fig. 18.9).

A small number of natural focal diseases are found almost everywhere. These are diseases whose pathogens, as a rule, are not associated in their development cycle with external environment and infect a wide variety of hosts. Diseases of this kind include, for example, toxoplasmosis And trichinosis. A person can become infected with these natural focal diseases in any natural climatic zone and in any ecological system.

The absolute majority of natural focal diseases affect a person only if he gets into the corresponding focus (while hunting, fishing, V hiking trips, in geological batches, etc.) under the conditions of his susceptibility to them. So, taiga encephalitis a person becomes infected when bitten by an infected tick, and opisthorchiasis - having eaten insufficiently heat-treated fish with cat fluke larvae.

Prevention of natural focal diseases presents particular difficulties. Due to the fact that a large number of hosts and often vectors are included in the circulation of the pathogen, the destruction of entire biogeocenotic complexes that arose as a result of the evolutionary process is ecologically unreasonable, harmful and even technically impossible. Only in cases where the foci are small and well studied, is it possible to comprehensively transform such biogeocenoses in a direction that excludes the circulation of the pathogen. Thus, the reclamation of desertified landscapes with the creation of irrigated horticultural farms in their place, carried out against the background of the fight against desert rodents and mosquitoes, can sharply reduce the incidence of leishmaniasis in the population. In most cases of natural focal diseases, their prevention should be aimed primarily at individual protection (prevention from bites by blood-sucking arthropods, heat treatment food products etc.) in accordance with the circulation paths in nature of specific pathogens.