Epidemiology of natural focal infections. Natural focal vector-borne infectious diseases
NATURAL FOCAL DISEASES
NATURAL FOCAL DISEASES infectious diseases that exist in natural foci due to persistent foci of infection and invasion supported by wild animals. These include: tick-borne and mosquito (Japanese) encephalitis, tick-borne rickettsiosis (typhoid fever), various forms tick-borne relapsing fever, tularemia, plague, hemorrhagic fever, African trypanosomiasis, diphyllobothriasis, opisthorchiasis and other pathogens, carriers, donor animals and recipients are more or less permanent members of the biocenoses of a certain geographical landscape. The doctrine of natural focal disease was developed by E. N. Pavlovsky (1938) and his school.
Ecological encyclopedic dictionary. - Chisinau: Main edition of the Moldavian Soviet Encyclopedia. I.I. Grandpa. 1989
- NATURE
- NATURAL FACTORS OF THE EPIDEMIC PROCESS
See what "NATURAL FOCAL DISEASES" is in other dictionaries:
Natural focal infection (diseases natural focal)- diseases spread in the focus on the territory of which the pathogen constantly circulates among certain animal species, spreading, as a rule, by arthropod vectors ... Civil protection. Conceptual and terminological dictionary
Infectious human diseases occurring in certain areas where natural, climatic conditions and other factors ensure the circulation of the pathogen among animals for an indefinitely long time. Edwart. Dictionary… … Emergencies Dictionary
Hemorrhagic fevers- sharp infectious diseases viral nature, characterized by toxicosis, fever and hemorrhagic syndrome with the outflow of blood from the vessels (bleeding, hemorrhage). Pathogens belong to the group of arboviruses, the reservoir of which ... ... Disease Handbook
Naturally focal viral diseases, characterized by the development of hemorrhagic syndrome against the background of an acute fever. The viruses causing G. of l. belong to 7 sorts of 5 virus families (see. Viral infections). According to the mechanism of transmission ... ... Medical Encyclopedia
Plague bacillus under fluorescence microscopy. ICD 10 ... Wikipedia
public health- (population or population health) the main feature, the main property of the human community, its natural state, reflecting the individual adaptive reactions of each member of the community of people and the ability of the entire community to ... ... human ecology
Rabies- natural focal infection. Keepers of the rabies virus are wild and domestic animals. The main carriers and keepers of the rabies virus are foxes in the wild, and from domestic animals - cats.
The rabies virus is bullet-shaped and belongs to the RNA viruses. Hosts of the disease shed the virus in saliva and are contagious during the last week incubation period and throughout the illness. Distributed everywhere.
Entry gates of infection are damaged by a bite skin and mucous membranes. From the point of entry, the virus spreads to the nerve endings, then moving along the nerves penetrates the spinal cord and brain. The incubation period lasts 10-90 days, in rare cases - more than 1 year.
Symptoms of rabies. Convulsive contractions of the swallowing muscles, a feeling of fear, convulsions, shortness of breath. Attacks of hydrophobia first occur when trying to drink, then even at the mention of it. Attacks are painful. During attacks, violent excitement occurs - patients break furniture, throw themselves at people, injure themselves, showing superhuman strength. Then comes a "quiet" period - a sign of the onset of ascending paralysis, which subsequently captures the respiratory muscles, which leads to respiratory arrest and death of the patient. Less common is the initially "silent", paralytic form of rabies.
Rabies is a lethal disease. That is why the introduction of the vaccine (and immunoglobulin in special cases) in the first hours after the bite is extremely important. Preventive vaccination is also possible.
Leishmaniasis is a transmissible disease with natural foci.
The source of infection in the city is sick people and dogs. In rural areas - various rodents. The disease occurs in some areas of Turkmenistan, Uzbekistan, Transcaucasia, Africa and Asia. Outbreaks of the disease are common from May to November - this seasonality is associated with the biology of its vectors - mosquitoes.
There are two main clinical forms leishmaniasis: visceral and cutaneous.
Internal leishmaniasis. A typical symptom is a sharply enlarged spleen, liver and lymph nodes. The temperature is remitting with two or three rises during the day. The incubation period lasts from 10-20 days to several months. The disease begins with increasing weakness, intestinal upset (diarrhea). The spleen gradually increases and by the height of the disease reaches a huge size and high density and descends into the small pelvis. Various types of rashes appear on the skin, mostly papular. The skin is dry, pale earthy in color. A tendency to bleeding is characteristic, cachexia (weight loss), anemia, and edema gradually develop.
Cutaneous leishmaniasis. The incubation period is 3-8 months. Initially, a tubercle with a diameter of 2-3 mm appears at the site of the introduction of the pathogen. Gradually, it increases in size, the skin above it becomes brownish red, and after 3-6 months. covered with a scaly crust. When it is removed, an ulcer is formed, which has a round shape, a smooth or wrinkled bottom, covered with a purulent coating. An infiltrate is formed around the ulcer, during the decay of which the size of the ulcer gradually increases, its edges are undermined, uneven, and the discharge is insignificant. Gradual scarring of the ulcer ends about a year after the onset of the disease. The number of ulcers is from 1-3 to 10, they are usually located on open areas of the skin accessible to mosquitoes (face, hands). Pavlovian transmissible infectious malaria
Zoonotic (rural) cutaneous leishmaniasis. The incubation period is shorter. At the site of the introduction of the pathogen, a cone-shaped tubercle with a diameter of 2-4 mm appears, which grows rapidly and after a few days reaches 1-1.5 cm in diameter, necrosis occurs in its center. After rejection of dead tissue, an ulcer opens, which expands rapidly. Single ulcers are sometimes very extensive, up to 5 cm in diameter or more. With multiple ulcers, and with this type of leishmaniasis, their number can reach several tens and hundreds, the size of each ulcer is small. They have uneven undermined edges, the bottom is covered with necrotic masses and abundant serous-purulent discharge. By the 3rd month, the bottom of the ulcer is cleared, granulations grow. The process ends after 5 months. Often observed lymphangitis, lymphadenitis. Both types of cutaneous leishmaniasis can develop a chronic tuberculoid form resembling lupus.
The diagnosis of cutaneous forms of leishmaniasis is established on the basis of characteristic clinical picture, confirmed by the detection of the pathogen in the material taken from the nodule or infiltrate.
For the treatment of patients with cutaneous leishmaniasis, monomycin is prescribed intramuscularly at 250,000 units. 3 times a day for 10-12 days. Monomycin ointment is applied topically.
Prevention. Fight against mosquitoes - carriers of the pathogen, destruction of infected dogs and rodents. Recently, prophylactic vaccinations with live cultures of Leishmania have been used.
Malaria- a transmissible human disease of protozoal etiology, characterized by a predominant lesion of the reticulohistiocytic system and erythrocytes, febrile attacks, anemia, enlargement of the liver and spleen.
The causative agent of four-day malaria is a microorganism, the species Plasmodium malariae.
Plasmodium malariae are more often found in the southern regions of the CIS, in countries with temperate climate- less often. Fatal outcomes are rare.
Carriers are mosquitoes of the genus Anopheles. The incidence directly depends on the size of the mosquito population and the number of patients serving as a reservoir of infection. In connection with the development of the tourism industry, the incidence is detected in countries outside the natural range. The transmission of an infectious agent in most cases is horizontal.
Tick-borne encephalitis- viral, natural-focal disease with a primary lesion of the central nervous system(CNS). The carriers of the infection are ixodid ticks, the virus is transmitted by the bite of a sick tick. The infection also affects animals - rodents, livestock, monkeys, some birds.
The causative agent of infection is viruses of the Flaviviridae family. There are two geographical, clinical and biological variants of the virus and disease. The Far East, the most severe variant of tick-borne encephalitis, first described by the expedition of the famous Russian immunologist L. Zilber, was identified in Primorsky and Khabarovsk Territories in 1931 and called "taiga spring-summer encephalitis." At the same time, in 1931, in Austria, Schneider described a seasonal outbreak of meningitis, later identified as the European variant of tick-borne encephalitis. Later, in 1939, tick-borne encephalitis was detected in the European part of Russia and in most European countries. The tick-borne encephalitis virus itself was first isolated in 1949.
Reservoirs and carriers of infection in nature are ixodid ticks. After bloodsucking on a sick animal, after 5-6 days the virus penetrates into all organs of the tick, concentrating in the genital apparatus, intestines and salivary glands(which explains the transmission of the virus to humans by a tick bite). Human infection can also occur by crushing and rubbing a sucked tick, by eating infected raw goat and cow's milk. Infection can also occur without visiting the forest - a tick can be brought from the forest with branches, on the hair of domestic animals, etc.
The virus persists throughout the life of the tick, that is, for 2-4 years, is transmitted from generation to generation, which makes ticks a "valuable" natural reservoir of infection. Tick infection is heterogeneous from region to region and from season to season, ranging from 1% to 20%.
If infection occurs through milk (some experts even distinguish this route of infection and the form of the disease as a separate infection), the virus first penetrates into all internal organs, causing the first wave of fever, then, when the virus reaches its final target, the CNS - the second wave of fever. If the infection did not occur with food (not through the mouth), another form of the disease develops, characterized by only one wave of fever, due to the penetration of the virus into the brain and spinal cord and inflammation in these organs (encephalitis itself from the Greek "enkephalon" - the brain) .
The incubation period of the disease averages 1.5-2 weeks, sometimes dragging on up to 3 weeks. The different duration of the incubation period can be explained by the nature of the bite - the longer the tick sucked, the more viruses entered the body and the faster the disease will develop.
The disease develops acutely, within a few days. The virus infects the gray matter (cortex) of the brain, motor neurons spinal cord and peripheral nerves, which is clinically expressed in convulsions, paralysis of individual muscle groups or entire limbs and impaired skin sensitivity. Later, when viral inflammation covers the entire brain, persistent headaches, persistent vomiting, and loss of consciousness are noted. up to a coma or vice versa, psychomotor agitation develops with a loss of orientation in time and space. Later there may be disturbances of cardio-vascular system(myocarditis, cardiovascular insufficiency, arrhythmia), digestive system- stool retention, enlargement of the liver and spleen. All of these symptoms are observed against the background of toxic damage to the body - an increase in body temperature to 39-40 ° C. In a small percentage of cases, with a lesion spinal nerves, the disease can proceed according to the type of "radiculitis" (polyradiculoneuritis).
Complications of tick-borne encephalitis are observed in 30-80% of those who have been ill and are mainly represented by flaccid paralysis, mainly upper limbs. Mortality ranges from 2% in the European form to 20% in the Far Eastern form. Death occurs within 1 week of onset. Atypical forms of the disease are possible - erased, poliomyelitis-like. It is also possible to develop chronic carriage of the virus. Persons whose activities are associated with being in the forest are most at risk - employees of timber industry enterprises, geological exploration parties, builders of roads and railways, oil and gas pipelines, power lines, topographers, hunters, tourists. AT last years there is a predominance among the sick townspeople. Among the patients, up to 75% are city dwellers who became infected in suburban forests, in garden and garden plots.
Leptospirosis- infectious, natural-focal disease of animals, birds, people. It is a predominantly acute disease characterized by transient fever, anemia, jaundice, hemoglobinuria, hemorrhagic diathesis, necrosis of the mucous membranes and skin, atony of the digestive organs, reduction or complete cessation of lactation and progressive emaciation.
Leptospirosis of farm animals, dogs, cats, fur animals. In the CIS, the disease often causes damage to livestock.
The stability of the pathogen in relation to the effects of physical and chemical factors corresponds to the resistance of vegetative forms of bacteria. In the urine of cattle, pigs and rodents, they persist from 4 hours to 6-7 days; in the kidneys of the same animal species - from 12 hours to 12 days; in the aborted fetus of a pig - several days; in the pericardial fluid of a piglet - 6-15 hours, in muscle tissue - 48 hours; in fresh milk - 8-24 hours; in frozen semen - 1-3 years (observation period).
Leptospira are typical hydrobionts. In sterile water, they persist for 21-99 days, in tap water - 7-30 days, in the water of rivers and lakes - from 2 to 200 days.
Under natural conditions, pigs and cattle are more likely to suffer from leptospirosis. Sources and reservoirs of pathogenic leptospira are both agricultural and wild animals. They release the pathogen into the external environment in various ways: with urine, feces, milk, semen, through the lungs, with outflows from the genitals.
Asymptomatically sick leptospiro-carrier animals represent a special epizootological and epidemiological danger. The period of leptospiron carriage after a disease or latent infection is quite long: in cattle 1.5-6 months; in sheep, goats - 6-9 months; in pigs - from 15 days to 2 years; in dogs - from 110 days to 3 years; in cats - from 4 to 119 days; in chickens, ducks, geese - from 108 to 158 days. In humans, leptospiron carriage lasts from 4 weeks to 11 months.
Leptospira released from the body of sick animals and microcarriers infect water, feed, pastures, soil, bedding, and other environmental objects through which healthy animals become infected. Among these factors of transmission of the pathogen, the waterway is the main one. Of particular danger are non-drying puddles, ponds, swamps, slowly flowing rivers, and wet soil.
Animals become infected with leptospirosis more often at a watering place, when eating the corpses of rodents - leptospirosis carriers or feed infected with the urine of these rodents.
Game animals with their cellular content become infected mainly when eating the products of slaughter of animals with leptospirosis; pigs - while swimming in open water, young animals - when drinking milk from sick mothers.
It is also possible intrauterine infection in cattle, sheep and pigs. The possibility of sexual transmission of the pathogen has been proven.
Leptospira penetrate into the body of animals and humans through damaged areas of the skin (scratches, cuts, wounds, bites), mucous membranes of the oral and nasal cavities, eyes, genital tract and through the gastrointestinal tract.
Leptospirosis is more common in areas where the soil is moist, contains a lot of humus, and has a neutral or slightly alkaline reaction.
The disease is observed at any time of the year, but in animals with grazing - mainly in the summer-autumn period. Thus, an analysis of the incidence of leptospirosis in cattle in Russia shows that in June-September 77% of diseased animals occur. The seasonal dynamics of the disease in various natural and economic zones is not the same.
Leptospirosis of pigs is one of the diseases without pronounced seasonality, manifested with equal intensity throughout the year. This is due to the fact that the water factor in the spread of the disease among pigs is much less important than for animals of other species.
Leptospirosis manifests itself in the form of small epizootics and sporadic cases. A characteristic feature of an epizootic is that at first a small group of animals falls ill within 5-10 days, then the outbreak subsides, but after a few days it repeats again. This circumstance is associated with the accumulation of the infectious agent in the external environment, because. the duration of the pause is approximately equal to the incubation period.
Another feature of the epizootic is that it does not cover the entire livestock or even the vast majority of the herd. This indicates a significant immune layer among animals.
The main epizootological feature of leptospirosis in farm animals at present is the predominance of asymptomatic forms of infection in the form of leptospirosis and leptospirosis immunizing subinfection.
People can become infected with leptospirosis while swimming in shallow stagnant waters contaminated with leptospira, when using water for washing, drinking, washing, etc.
Leptospira penetrate the human body in various ways: through damaged skin, mucous membranes of the gastrointestinal tract, respiratory and genital tract, conjunctiva. In the temperate zone, the disease is recorded more often in June-August.
Clinically, leptospirosis is characterized by a sudden onset, fever (38.5-40 "C), flushing of the face and throat, injection of conjunctival vessels, stiff neck and chills.
A few days later, a polymorphic rash appears on the skin, severe pain in the thigh and calf muscles. General weakness, jaundice, significant headache, loss of appetite, nausea, and vomiting develop. The liver is enlarged.
Natural focal infectious diseases called diseases in which the source of infection is in nature. Most often these are warm-blooded wild animals, for some diseases - blood-sucking insects, mainly ticks. The area of each infection is limited to a certain ecological and geographical area.
The transmission of the pathogen to humans occurs through the bites of infected insects (ticks, fleas, mosquitoes, mosquitoes, etc.); at the use of the water contaminated by sick animals, food; through household items; in direct contact - contact with the pathogen.
Domestic scientists Deminsky, Zabolotny, Klodnitsky made a major contribution to the study of epidemiology and clinical manifestations these diseases. In the middle of the XX century. Soviet scientists carried out a huge expeditionary work to study tick-borne taiga encephalitis, as well as Far Eastern hemorrhagic nephrosonephritis, now called hemorrhagic fever with renal syndrome (HFRS).
Plague- natural focal infection, belonging to the group of especially dangerous. Mortality in Asia and Africa ranges from 2 to 25%, and during the period of plague epidemics in the past it reached almost 100%. In natural foci, rodents and lagomorphs are the source of infection. different types. Natural plague infection has been registered in almost 250 species of wild animals, from which city rodents - rats and mice - get the pathogen. Plague is transmitted to humans by flea bites.
The epidemiological situation of plague in Russia can be considered unstable due to the isolation of the causative agent of the disease from natural foci of infection and the real danger of importing plague from abroad. On the territory of Russia, 11 permanent plague foci have been registered. The total area of natural plague foci in Russia is over 31 million hectares. The most extensive focal territories are located in the European part of Russia (steppe, semi-desert and desert regions of the Caspian Sea and Ciscaucasia).
Tularemia characterized by intoxication, fever, lymph nodes. The causative agent of the disease is a small bacterium. Due to the wide spread of tularemia, despite the absence of lethal outcomes, it posed a danger to the population and the military contingent. The disease is polyzonal.
The epizootic and epidemiological features of tularemia are associated with the natural infection of about 125 species of vertebrate animals, mainly representatives of the rodent order, with its pathogen. Among these animals, the most susceptible to the causative agent of tularemia are water rats, hares, muskrats, etc.
The causative agent of tularemia, as well as the causative agent of plague, is transmitted to humans by transmissible, contact, oral and aspiration routes. The transmission mechanism of infection transmission is carried out through ticks (mainly ixodid) and flying blood-sucking Diptera (mosquitoes, horseflies). The preservation of the pathogen and its transmission to humans are carried out with the participation of blood-sucking arthropods, through air and food contaminated with rodent excrement.
The forest zone is characterized tick-borne encephalitis and tick-borne borreliosis. The main mechanism of pathogen transmission is aspiration. The causative agent is released into environment with animal feces and saliva.
For the tundra rabies, transmitted to humans through the bite of canines, and tumor-like liver damage alveococcosis caused by a tapeworm larva.
1) Diseases of endogenous origin
BUT) hereditary diseases: ubiquitous (everywhere), marginal
B) Association with damage to the fetus in the womb
2) Exogenous origin
A) Diseases associated with the action of environmental factors: geophysical, geochemical (terr, poor in iodine ...), especially food regimes, poisons, growing, alive, allergens, injuries due to natural disasters
B) connection with the action of technological factors
The founder of the doctrine of the natural focality of human diseases was D.K. Zabolotny, who first described this phenomenon in 1922 using the example of the spread of the plague. But a harmonious doctrine of natural focal diseases was created by E.N. Pavlovsky (1939). It has gained worldwide fame and recognition. Numerous students and followers of E.N. Pavlovsky in our country and abroad studied the natural foci of many contagious human diseases. The works of E.N. Pavlovsky were summarized in the monograph "Natural foci of vector-borne diseases in connection with the landscape epidemiology of zooanthroponoses" [Pavlovsky, 1964].
In most zooanthroponoses, the place of stay of a sick person is not an epidemic focus, since a person, with a few exceptions (for example, with plague, yellow fever), does not serve as a source of the infectious agent. The main role in the mechanism of transmission of natural focal zooanthroponoses is played by the natural focus of the disease.
The existence of natural foci of diseases is due to the continuous circulation of their pathogens among vertebrates - more often rodents, birds, as well as ungulates, predators and others, which serve as sources (reservoirs) 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 ways and factors of pathogen transmission are possible, for example, through water, food, contact, etc.
People or pets can become infected with natural focal diseases when they enter the territory of a natural focus. Infection of people is also possible from domestic animals infected with a natural focal disease.
On the territory of Russia there are more than 40 natural focal diseases of people, represented by infections and invasions. Among them, the most common and studied are tick-borne encephalitis, Japanese encephalitis, many tick-borne rickettsiosis, plague, rabies, leptospirosis, hemorrhagic fevers, tularemia, tick-borne relapsing fever, Lyme disease and others, as well as a number of helminthiases - diphyllobothriasis, trichinosis, alveococcus. goats, paragonimiasis, metagonimiasis, etc. The following transmissible infectious diseases are recorded in tropical and subtropical regions: Dengue fever, yellow fever, Ebola fever, mosquito encephalitis, St. ( sleeping sickness and others), Chagas disease, etc. The most susceptible to many natural focal diseases are people who arrived at the outbreak from outside, which is taken into account when determining persons to be immunized.
At present, the situation with infectious diseases, known since ancient times, has fundamentally changed. Epidemics of many infectious diseases gradually died out as a result of advances in preventive and curative medicine, as well as the formation of herd immunity, so they remained only in world history and the history of epidemiology. At the same time, as a result of complex biological processes, new infectious diseases have appeared and are emerging, to which humans have no immunity. It is these diseases, the sources of which are most often migrants from tropical and subtropical regions of our planet, that pose the greatest threat to residents of territories with a temperate climate. From the central regions of Africa appeared HIV infection. There is a threat of infection with Ebola, Marburg, Dengue, yellow fever.
Modern vehicles, especially aviation, can not only deliver an infected migrant from an endemic focus to Russia in a few hours, but also transport an infection carrier, for example, the Aedes aegypti mosquito, which is the custodian of the causative agent of malaria, yellow fever and other infections.
Oligotrophic Reservoirs
water bodies with a low level of primary production. Oligotrophic include waters that occupy large areas in the central subtropical regions of the World Ocean, the primary productivity of which is low due to a lack of nutrients is low. Among continental water bodies, oligotrophic water bodies usually include lakes and mountain rivers with cold, oxygen-rich, nutrient-poor, clear water. The maximum primary production of oligotrophic water bodies is 0.1-0.3 gC/m2 per day. The mass of phytoplankton in oligotrophic water bodies is small, but its species diversity can be high. Hydrobionts are represented by oxyphilous forms: chironomid larvae are usually tanitharzus, fish are whitefish and salmon. Freshwater oligotrophic reservoirs are valuable as a source of clean water.
The doctrine of natural focal diseases
At the end of the 30s. 20th century E. N. Pavlovsky formulated the doctrine of the natural focality of diseases, the essence of which lies in the discovery of the phenomenon of a natural focus.
The natural focus of the disease is the smallest part of one or more geographical landscapes inhabited by wild warm-blooded animals susceptible to this infection and arthropods and insect vectors, among which the pathogen circulation proceeds indefinitely due to a continuous epizootic process. Natural foci of disease arose on Earth long before the appearance of man and exist independently of him.
An important epidemiological feature of natural focal diseases is their territorial confinement to certain geographical landscapes, to which natural foci are attached. For example, foci of tick-borne encephalitis are confined to the forest and forest-steppe zones, foci of tick-borne rickettsiosis in North Asia - to the steppe landscapes of Siberia and Far East, yellow fever - to the zone of tropical rainforests, etc. Natural focal infections are divided into endemic zoonoses, the range of which is associated with the range of animal hosts and vectors (for example, tick-borne encephalitis), and endemic metaxenosis associated with the range of animals, the passage through the body of which is an important condition for the spread of the disease (for example, yellow fever). When a person appears at a certain time in the focus of a person, carriers can infect him with a natural focal disease. So zoonotic infections become anthropozoonotic.
Classification of natural foci
1. By the nature of the development of the landscape
Anthropurgic foci.
The spread of pathogens is carried out by domestic and wild animals. Occurs when a person develops the territory of the software. Such a character can acquire foci of Japanese encephalitis, cutaneous leishmaniasis, tick-borne relapsing fever, etc.
synanthropic foci.
The circulation of pathogens is associated only with domestic animals. Foci of toxoplasmosis, trichinosis.
2. By the number of hosts
Monosteel.
Polygostal.
Several species of animals serve as a reservoir (ground squirrels, marmots, tarbagans, gerbils in the natural focus of the plague).
3. By the number of carriers
Monovector.
Pathogens are transmitted by only one type of carrier. It is determined by the species composition of carriers in a particular biocenosis (only one species of ixodid ticks lives in a certain focus of taiga encephalitis).
Polyvector.
The pathogens are transmitted by various types of vectors. (Tularemia software - vectors: different kinds mosquitoes, horseflies, ixodid ticks).
vector-borne diseases
Vector-borne diseases are infectious diseases transmitted by blood-sucking insects and representatives of the arthropod type. Infection occurs when a person or animal is bitten by an infected insect or tick.
There are about two hundred official diseases that have a transmissible transmission route. They can be caused by various infectious agents: bacteria and viruses, protozoa and rickettsia*, and even helminths. Some of them are transmitted through the bite of blood-sucking arthropods (malaria, typhus, yellow fever), some of them - indirectly, when cutting the carcass of an infected animal, in turn, bitten by an insect vector (plague, tularemia, anthrax). Such diseases are divided into two groups:
- Obligately vector-borne diseases are those vector-borne diseases that are transmitted only with the participation of the carrier.
Japanese encephalitis;
Loose (lousy and tick-borne) typhus;
Relapsing (lousy and tick-borne) typhus;
Lyme disease, etc.
- Facultatively vector-borne diseases are vector-borne diseases that are spread by various means, including with the participation of vectors.
Brucellosis;
Tick-borne encephalitis;
Anthrax;
Tularemia, etc.
Carrier classification:
- Specific carriers ensure the transfer of the pathogen from the blood
sick animals or humans into the blood of healthy ones. In the body
specific carriers, the pathogen multiplies or accumulates. In this way, fleas transmit plague, lice transmit typhus, mosquitoes transmit Papatachi fever. In the body of some carriers, the pathogen goes through a certain development cycle. So, in the body of a mosquito of the genus Anopheles, the malaria plasmodium performs a sexual development cycle. Along with this, in the body of ticks, the causative agents of tick-borne encephalitis and some rickettsiosis not only multiply and accumulate, but are also transmitted to a new generation through the egg (transovarially). Therefore, the pathogen in the body of a specific carrier can persist (with some exceptions) throughout the life of the carrier;
- Non-specific (mechanical) carriers that perform
mechanical transfer of the causative agent of the disease without its development and reproduction (gadflies, autumn zhigalki and ixodid ticks for causative agents of tularemia, brucellosis, anthrax).
And also vector-borne diseases are divided into two groups depending on pathogens:
- Invasions (pathogens - such animals);
- Infections (causative agents - viruses, rickettsia and bacteria).
Transmissible epidemics and their causes
The territorial and seasonal limitation of vector-borne diseases is determined by the prevalence of the carrier. The greatest epidemiological danger to humans is posed by blood-sucking arthropods (type Arthropoda), which include a) the class of arachnids and b) the class of insects. Diptera arthropods are more active in nature, therefore they are able to cause a short time large outbreaks of a number of diseases among people (tularemia, cutaneous leishmaniasis, mosquito fever, Japanese encephalitis, etc.). These insects can be blown over long distances from the outbreaks and transmit diseases there. Ixodid and argas ticks mainly pose an epidemiological hazard when visiting the territories of outbreaks and caring for domestic animals (cattle, etc.).
Flying insects mosquitoes, mosquitoes, midges, horseflies, biting midges, blood-sucking flies are the most active carriers. So, mosquitoes are able to fly up to a distance of 3-5 km from the place of their breeding. Horseflies, chasing animals, can move for tens of kilometers, alternating active flight with passive transportation on the animals themselves. Mosquitoes are carriers of pathogens of malaria, tularemia, WNV*, mosquito encephalitis. Midges, midges, horseflies are able to participate in the transfer of pathogens of tularemia, mosquitoes - pathogens of leishmaniasis.
Of the non-flying arthropods, ticks and fleas represent the greatest epidemiological danger. Ticks attack a person when he actively penetrates into their habitat and transmit pathogens to a person. hemorrhagic fever Crimea-Congo, Q fever, tick-borne encephalitis. Fleas are transmitted pathogens of plague, flea-rat rickettsiosis. Lice are carriers of pathogens of epidemic typhus and lousy relapsing fever, trench fever.
