Waterborne infections. State Budgetary Institution of Healthcare Leningrad Central District Hospital of the Ministry of Health of the Krasnodar Territory. The equation for the electrodiffusion of ions through a membrane in the approximation of a uniform field

WHO experts have established that 80% of all diseases in the world are associated with the poor quality of drinking water and violations of sanitary and hygienic standards of water supply. The prevalence of infectious diseases transmitted through water, despite the measures taken, is extremely high throughout the world. Thus, the number of people suffering from malaria is 800 million, trachoma - 500 million, schistosomiasis - 200 million, gastroenteritis - 400 million. At the same time, 4 million children and 18 million adults die from gastroenteritis every year. In general, water-related diseases affect half of humanity - about 2 billion people. The situation is especially dangerous in rural areas, where only a third of the inhabitants have access to safe water supply systems and only 13% are provided with sewerage. From 1971 to 1978, in the most favorable country in the world in terms of water supply, the United States, 202 epidemics were registered, covering 50 million people. Historically, the role of water in the transmission and spread of infectious diseases was known to Hippocrates in the 4th century BC. However, the first reliable description of the water epidemic was made only in the 19th century by the English scientist Snow. It concerned the cholera epidemic in London in 1854, when within 15 days 457 people died from this disease, using water from one well, into which sewage from a cesspool leaked.

The final proof of the epidemiological role of water was obtained by R. Koch in 1883. Studying the outbreak of cholera in India, he found the causative agents of this disease not only in the discharge of patients, but also in the water of the pond, which was used by all the sick. A few years later, R. Koch isolated a vibrio from the water of the Elbe River during a cholera epidemic, when more than 17,000 people fell ill at the same time, of which 8,605 died.

Water-borne diseases are very numerous. All of them can be divided into several main groups. First of all, these are intestinal infections of a bacterial nature, which include cholera, typhoid fever, paratyphoid fever A and B, dysentery, various enteritis and enterocolitis. For the occurrence of these diseases, unorganized water consumption, insufficient amount of water, appropriate natural conditions for the spread and survival of an infectious agent in environmental objects, technical violations at water intake, water treatment facilities and water pipes, non-observance of elementary standards of personal hygiene are favorable. The development of epidemics of intestinal diseases of water origin has certain features. Outbreaks of such infections begin suddenly, almost simultaneously many people who take water from one contaminated source fall ill. After carrying out anti-epidemic measures aimed at eliminating water use from an infected source, disinfection, water protection measures, as well as treating patients and limiting their contacts, the number of cases is rapidly decreasing. However, for some time, the incidence remains at a relatively low level due to contact household infection. Cholera is traditionally considered the most dangerous intestinal disease of water origin. This disease covers vast expanses, affecting the population of entire countries and continents.

Due to the severity of the clinical course and the trend towards pandemic spread, cholera is a particularly dangerous infection. As indicated, cholera was known even before our era. However, the first pandemic began in 1817 in India and, due to the development of trade relations, religious pilgrimages, and migration of the population, quickly spread throughout the world, ending only in 1823. In total, 6 pandemics of classical Asian cholera were recorded in the history of observations. The last of them, which lasted from 1902 to 1926, captured Asia, Africa and Europe. These epidemics have cost humanity more than 10 million lives. Since 1961, there has been an increase in the epidemic process of cholera. This is explained by the spread from about. Sulawesi disease caused by a less pathogenic, but more resistant Vibrio El Tor. The homeland and constant focus of cholera are the coastal regions of the Ganges and Brahmaputra rivers. However, during each of the 6 pandemics, the epidemic process also captured Russia, spreading through Afghanistan and Iran to the Orenburg steppes or to the Transcaucasus, to the Black Sea coast and to the Volga region inland. Large water cholera outbreaks occurred in St. Petersburg in 1908-1909 and in 1918, when polluted water from the Neva got into the water supply network and water chlorination was disrupted. In recent years, only isolated "imported" cases of cholera have been noted in Russia.

High morbidity and mortality are also characteristic of typhoid and paratyphoid A and B. The causative agents of these diseases are microbes of the genus Salmonella of the family of intestinal bacteria, which are very resistant to external influences. The death of microorganisms accelerates with an increase in the ambient temperature. So, in cold clean water, typhoid pathogens persist for up to 1.5 years, withstand freezing for several months and can overwinter in ice. In tap water, they are viable for up to 3 months. , and in the water of open reservoirs - up to 12 days. Water epidemics of typhoid-paratyphoid diseases can cover different groups of the population, depending on the power of the water supply source. The use of contaminated water from ditches, ponds, wells leads to the disease of tens, and sometimes hundreds of people. However, if rivers and reservoirs or the drinking water of the central water supply are polluted, then an epidemic of typhoid fever can cover thousands and tens of thousands of people. One of the largest acute epidemics of typhoid fever was an epidemic of water origin in Barcelona and 1914, when 18,500 people fell ill at the same time, of which 1,847 died. A severe epidemic was noted in 1926 in Hannover, where polluted river water got into tap water. As a result, 2,500 people fell ill with typhoid fever, of which more than 10% died.

In Russia, epidemics of typhoid fever in different years also covered a significant part of the population. A sad championship in this regard belonged to St. Petersburg, where about 1,000 people died every year when using polluted water due to violations of the water supply network at the beginning of the 20th century. As the defects in the water supply were eliminated, a rapid decrease in the incidence began. The epidemic of typhoid fever in Rostoven-Don in 1926 was recognized as a classic in terms of the development of the epidemic process, where, as a result of sewage suction from a disturbed sewer into the water supply network, about 3,000 people fell ill at the same time. After the liquidation of the emergency situation, individual contact cases of typhoid fever were noted for several more months. It should be noted that paratyphoid infections as independent infections are extremely rare. They usually accompany outbreaks of typhoid fever. A similar picture was noted in Rostov-on-Don. Actively carried out after the Second World War, anti-epidemic measures have sharply reduced the level of typhoid and paratyphoid diseases. However, even in modern conditions, isolated outbreaks of typhoid fever are noted. An example is the epidemic in the Swiss city of Zermatt in 1963, which affected more than 400 people. The reason was the flushing of sewage from the latrine into the river, which was used for water supply.

Until now, the water way of transmission of dysentery has a certain importance, although it is much less important than the food or household contact. Dysentery is an acute infectious disease caused by microorganisms from the genus Shigella and manifested by damage to the colon and general intoxication of the body. The historical name of the disease (Greek “intestinal disorder”) belongs to Hippocrates (460-377 BC). However, even now, according to WHO, in dozens of countries around the world, more than 150,000 people suffer from dysentery every year. Since the beginning of the 60s of the XX century, Sonne's dysentery has taken the first place in distribution in developed countries, including North America and Europe. Shigella Flexner dysentery predominates in most countries in Africa, Asia, and Latin America. In some African countries, there are diseases caused by the pathogen Grigoriev-Shiga. In some cases, drinking water is involved in the transmission of colienteritis, diseases caused by enteropathogenic Escherichia coli. Outbreaks of these diseases are typical for young children who are in closed communities (children's homes, nurseries, kindergartens), where elementary rules of personal hygiene are not observed.

Many viral diseases are spread by water. These are infectious hepatitis (Botkin's disease), poliomyelitis, adenovirus and enterovirus infections. The water route of transmission is most important for infectious hepatitis caused by type A virus, which, in contrast to serum hepatitis caused by type B virus and transmitted parenterally, is also called epidemic. Infectious hepatitis is accompanied by severe intoxication with a predominant lesion of the liver. The hepatitis virus is more resistant to environmental factors than the causative agents of bacterial intestinal infections. The virus retains pathogenicity after freezing for 2 years, is resistant to most disinfectants, and dies when boiled only after 30-60 minutes. In this regard, standard methods of water purification and disinfection are not always effective enough against the hepatitis virus, and colibacterial indicators may not reflect real contamination with viruses. An indicative case of an epidemic of infectious hepatitis of water origin was noted in India in the city of Delhi in 1955-1956. , where the number of cases exceeded 28,000 people. The reason was an accident at the sewage and treatment facilities and pollution of the Jamna River with sewage containing a viral infection. Despite the rather favorable colibacterial parameters, the outbreak of infectious hepatitis was extensive and prolonged. Outbreaks of epidemic hepatitis are more likely to occur in those settlements where small surface sources are used for household purposes, and water disinfection is not given due attention. On the contrary, the epidemic danger is sharply reduced with centralized water supply with strict adherence to the water purification regime, as well as with the use of underground interstratal waters.

The water way of transmission of such a dangerous disease as poliomyelitis is quite relevant. Water outbreaks of poliomyelitis have been noted in many countries of the world. It should also be borne in mind that enteroviruses and adenoviruses can spread by water, causing severe damage to the intestines, central nervous system, skin and mucous membranes in humans. Prevention of viral diseases is complicated by the lack of sufficiently reliable methods for isolating viruses from various environments of the biosphere. In countries with a hot climate, there are diseases related to kleptospirosis. These are Weil-Vasiliev's disease (ictero-hemorrhagic leptospirosis) and water fever (anicteric leptospirosis). Carriers of the infection are most often rodents, sometimes cattle, pigs. A person becomes infected through the water of stagnant reservoirs (lakes, ponds, swamps) and ground wells; contaminated with animal excreta. The causative agents of infection enter the body through the gastrointestinal tract, as well as when bathing through the mucous membranes of the lips, mouth, nose and damaged skin.

Some types of bacterial zoonotic infections have a waterway of distribution. Sources of pathogens can be rodents (tularemia) or cattle (brucellosis, anthrax). The pathogen can enter the body both through the gastrointestinal tract and through the skin. According to a number of authors, transmission of tuberculosis pathogens through water is possible, although the water route of infection is not considered the main one for this infection. The most massive entry of tuberculous bacteria into water bodies is associated with the discharge of untreated wastewater from tuberculosis hospitals. Protozoal invasions, that is, diseases caused by protozoa, are found mainly in the hot climate of Asia and Africa. Expressed forms of diseases appear relatively rarely, although the carriage, depending on sanitary well-being, can exceed 15%. These are amoebiasis or amoebic dysentery caused by Eniamoeba hislolytica, balantidiasis caused by the ciliate Balantidium coli, and giardiasis caused by the flagellate Lamblia intestinalis. Amoebiasis and balantidiasis develop as acute diseases that turn into a chronic form, accompanied by diarrhea, when protozoa enter with drinking water and penetrate into the mucous membrane of the colon. Sometimes diseases become protracted, recurrent. Giardia does not cause disturbances in the intestinal mucosa, so the disease does not have a clear clinical picture. There are pains in the abdomen and dyspeptic disorders, but more often giardiasis remains asymptomatic. The carriage of lamblia among the population is very high and averages about 15%, and in children's groups with unfavorable hygienic

Schistosomiasis dermatitis (bather's itch) is ubiquitous. Recently, in connection with bathing in stagnant and low-flowing water bodies contaminated with feces, cases of such dermatitis have been noted in the cities of Russia, especially in children. The main host in which schistosomes of this species reach sexual maturity are domestic and wild ducks. The intermediate host is a freshwater mollusk. Schistosoma larvae, released from the mollusk, penetrate into the human epidermis when bathing, causing severe itching, swelling and rashes. Repeated cases of infection are especially difficult due to severe sensitization of the body. However, the helminth does not go through the full cycle of development in the human body and dies, so the duration of the disease ranges from several hours to 2 weeks.

The main foci of dracunculiasis (guinea worm) are noted in the countries of Africa and Asia, especially in India. The source of the disease is a sick person. The intermediate host is a microscopic freshwater cyclops crustacean. Infection occurs when water containing cyclops is used for drinking or bathing. The larvae penetrate intact human skin and mucous membranes and migrate through the lymphatic system into the subcutaneous tissue. An adult can reach 120 cm in length and stay in the human body for up to 14 months. The disease is accompanied by swelling, itching, suppuration of the skin and high sensitization of the body. In accordance with the cycle of development of the helminth and the human body, the disease can last more than a year. On the territory of the former USSR in Old Bukhara, the last centers of dracunculiasis were eliminated in 1932.

Waterborne infectious diseases include all diseases that can be contracted by drinking contaminated water or washing hands with it.
There are a lot of such diseases, and they do not always spread only through water. Sometimes infection can be indirect, and sometimes it is directly related to the consumption of infected water.

Scale of the problem

In developing countries, 4/5 of all diseases are associated with poor-quality drinking water, and diarrhea ranks first among the causes of death.

Around the world, about 1.1 billion people do not have access to clean drinking water. According to statistics, 2,213,000 people die each year from waterborne infections.

According to WHO, about 2 billion people worldwide suffer from schistosomiasis, which they contracted through water.

Water becomes dangerous when sewage contaminated with microbes enters reservoirs.

Most often this happens when water is drawn into reservoirs from surface sources (for example, streams, lakes, etc.). Old water pipes can also become a source of infection, especially in our realities.

Regular preventive shutdowns of water lead to the fact that the contents of the sewer pipes seep not only into the ground through defects in the sewer system, but also into the pipes of cold and hot water supply (due to the difference in pressure). That's where this smell from the water comes from when it is finally turned on after work has been done.

However, there are other routes of infection, such as insufficiently washed hands or contaminated food.

Prevention of contamination from water

For drinking and cooking, it is important to use only well-purified water.

Only clean water should be used for drinking and cooking. Clearly, water-borne diseases can be minimized by careful disinfection.

During disinfection, pathogenic microbes are destroyed, so they cannot enter the human body and cannot multiply in the water supply system.

If the water in the reservoirs is not processed, then the risk of infection of the population will increase many times over.

There are two main methods of disinfection: ultraviolet irradiation and the use of chemicals (chlorine or ozone). The simplest ways to protect yourself from waterborne diseases are to wash your hands thoroughly before eating, after using the toilet and hygiene procedures, wash food with detergents before cooking, keep all kitchen utensils clean and, of course, drink clean water. bottled, boiled or passed through antibacterial filters. Take care of yourself and your loved ones!

Which doctor to contact

If you suspect an infectious disease (vomiting, diarrhea, fever, abdominal pain), you should contact an infectious disease specialist. Often these diseases are treated in a hospital. In addition, the patient is examined by a therapist, if necessary - by a neurologist, hepatologist, and other specialists.

Biological objects in natural water can be represented by bacteria, viruses and protozoa. The fact that water can be the cause of mass ("epidemic") diseases has been known since ancient times. Historically, the role of water in the transmission and spread of infectious diseases was known to Hippocrates in the 4th century BC. BC e. The first reliable description of a water infection was made in the 19th century. English scientist Snow. It concerned the cholera epidemic in London in 1854.

The water way of spreading intestinal infections is possible when the following conditions are combined:

· There is a possibility of pathogens entering the water with excretions of patients or bacillus carriers;

· Pathogens retain viability and virulence in water for quite a long time;

It will be possible for contaminated water to enter the human intestines.

In the presence of pathogens of infectious diseases in drinking water, water can serve as a source of their spread and is dangerous in epidemiological terms. Diseases such as cholera, typhoid fever, paratyphoid B, dysentery, tularemia, leptospirosis are transmitted through water. Of lesser but still definite importance is the water way of transmission for such diseases as brucellosis, hepatitis A and E, poliomyelitis.

In addition to the pathogens of cholera, typhoid fever, dysentery, so-called conditionally pathogenic microorganisms can be present in tap water, which can cause diseases under certain conditions. These are Proteus, Klebsiella, Citrobacter, Pseudomonas, Aeromonas, which have many features in common with true Escherichia coli - a recognized indicator of fresh fecal contamination. In addition to the so-called coliform microorganisms, there are other opportunistic pathogens in the water - clostridia, yersinia, fecal streptococcus, parahemolytic vibrio, hafnia. All these microorganisms can cause intestinal dysfunction with diarrhea, which in official medical statistics are classified as acute intestinal infections (AII) of unknown etiology. Every year in Russia, an average of 0.7 million people fall ill with acute intestinal infections, of which about 60% are young children; deaths among sick children reaches 4000 per year.

In recent years, large epidemics of typhoid fever, similar to those that occurred in the 19th and first half of the 20th century, are not recorded, and the remaining low incidence is associated not with water, but with contact transmission. Nevertheless, the epidemiological trouble for typhoid fever persists where there are prerequisites for its spread through drinking water.

The incidence of waterborne dysentery (Flexner's dysentery) remains high.

A relatively “young” (the first epidemic was described in 1943) epidemic disease is viral hepatitis A. A large number of cases of this disease occur when this pathogen is transmitted by water.

In recent years, among the infectious morbidity associated with the water factor, the proportion of Escherichiosis, deseterium-like diseases caused by pathogenic strains of Escherichia coli, has increased.

Table 1. The incidence of AII

Pathogenic organisms have a number of properties that distinguish them from chemical pollutants:

· Pathogenic organisms are presented as discrete organisms, and are not in the form of a solution;

· Pathogenic organisms often agglomerate or adsorb to suspended solids in water, so that the resulting infectious dose cannot be accurately calculated from their average concentration in water;

· The likelihood of being exposed to a pathogen depends on the degree of its invasiveness and virulence, as well as on the immunity of the individual exposed to the pathogen.

2.1 Entry of pathogenic microorganisms into water and their survival in the aquatic environment

At the same time, unpolluted rivers, lakes and reservoirs, in which normal flora and fauna develop, not only do not represent a favorable environment for the development of pathogenic pathogenic bacteria, but, on the contrary, are a powerful barrier preventing their spread. There are many factors that have a negative impact on the vital activity of pathogenic microbes.

Finally, in reservoirs and watercourses (especially when contaminated with a significant amount of fecal sewage), a large number of microbes develop that are antagonists against pathogenic bacteria. Antagonist microbes secrete various antibiotic substances into the water, as a result of which the life span of pathogenic bacteria in the water is significantly reduced.

Pathogenic microbes remain the longest in sterile water, where foreign microflora is completely absent. Thus, the antagonistic relationship between saprophytic microbes and pathogenic bacteria is explained by a seemingly paradoxical fact - the purer the water, the longer pathogenic microbes remain in it.

Thus, the most effective and powerful factor leading to the death of pathogens of infectious diseases in natural waters is the biological population of reservoirs and watercourses, which, in the course of their life activity and the established relationships of a symbiotic and antagonistic nature, leads to the disappearance of pathogenic microorganisms that have entered the natural water.

Pathogens of diseases enter the water of open reservoirs with wastewater from populated areas and individual facilities, mainly hospitals. The causative agents of tularemia, leptospirosis, brucellosis enter the water with the secretions of rodents and cattle, as well as with the corpses of dead rodents. Microorganisms that are the causative agents of water infections remain viable in water for a sufficiently long time. In this regard, in cases where untreated river water is used for drinking purposes or there are violations in the treatment of water in water pipes, as well as when contaminated well water is used, water mass outbreaks of gastrointestinal diseases can occur. There are also cases when the cause of the outbreak of intestinal diseases was the contamination of water in the water supply network.

Table 2. Survival of microorganisms in water

The largest number of pathogenic microorganisms entering water bodies is found in polysaprobic zones, then they gradually die off in mesosaprobic zones and are practically not found in oligosaprobic zones.

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1. The role of water in the transmission of infectious diseases

In the context of the rapid growth of cities, the rapid development of industry and agriculture, the construction of treatment facilities is sometimes delayed, as a result of which reservoirs become recipients of poorly treated wastewater. Water is polluted, and the processes of its self-purification from extraneous microflora, including pathogens, proceed much more slowly, because the extensive construction of hydroelectric stations, reservoirs, canals changes the hydrological regime of rivers, the biological and chemical composition of water. This means that the microbes that enter the reservoir now retain their pathogenic properties for a longer time. bacillus carrier water infection pathogenic

The causative agents of diseases, getting into the human intestine, find favorable conditions for reproduction there, as a result of which an acute intestinal disease occurs. Since a large number of people usually use one source of water supply, the way the disease spreads through water is the most massive, and therefore the most dangerous.

Human faeces and fecal sewage are the main sources of water-borne pathogens. Fecal contamination of water worsens its quality, and pathogenic microorganisms that enter the water with excretions of warm-blooded animals can cause an increase in the incidence of intestinal infections. Pathogenic microbes can get into open water bodies when sewage is discharged from ships, when coasts are polluted, when crossings are built, when cattle are watered, when washing clothes, bathing, when sewage is washed off the soil surface by atmospheric precipitation, etc.

Wherever organic waste accumulates (soil, open reservoirs, groundwater), conditions are created for maintaining the life of bacteria, and sometimes for their rapid development. Many of these microorganisms are harmless, but some of them have the ability to cause certain contagious diseases. Even in the presence of well-arranged and equipped filtration stations, equipped with the most advanced equipment and devices, with their impeccable operation, outbreaks and epidemics of intestinal diseases of water origin periodically occur in different countries.

Not everywhere the purification and disinfection of tap water is properly established. In some cases, good quality water enters the distribution network, which is then subjected to secondary bacterial contamination due to the significant deterioration of water pipes. In some settlements, part of the inhabitants use water from open reservoirs or technical water pipes for household and drinking purposes.

Causes of waterborne infectious diseases can be poor control of water treatment, pollution of the water collection system, pollution of the distribution system (tanks, pipes), consumption of surface water without treatment.

Well water is polluted when the contents of latrines, garbage pits and other sewage pits seep through the soil, contaminated water flows from the soil surface. Tap water can be polluted in case of accidents at head structures, sewage breakthroughs, groundwater suction, water flowing from the soil surface into manholes. Water pollution is possible during storage and transportation.

Water is one of the specific factors in the transmission of intestinal infections and, first of all, typhoid and paratyphoid diseases. Sanitary and epidemiological observations show that epidemic outbreaks occur not only with the direct use of contaminated water for drinking, but also with its indirect participation, i.e. when washing dishes, equipment and hands with it, when using contaminated water to prepare certain dishes. Violations in the centralized water supply system represent the greatest epidemiological danger. The use of water from technical water pipes for drinking and household purposes leads to serious consequences. The unsatisfactory sanitary condition of the water supply network, errors in its design and installation, improper operation can lead to contamination of water with pathogenic microbes. The causes of dysentery can be the use of water from open reservoirs, as well as the poor sanitary condition of wells and violation of the rules for using them.

Water-borne diseases cause ill health, disability and death in large numbers of people, especially children, predominantly in less developed countries where poor personal and communal hygiene is common. Many of these diseases, including typhoid fever, dysentery, cholera, schistosomiasis and hookworm, are transmitted to humans as a result of environmental pollution from human excreta. In most cases, the main carrier of the infectious principle is water. Success in the fight against these diseases or the achievement of their complete elimination depends on how the system for removing all metabolic products excreted from the human body is organized, how the matter of purifying water and protecting it from pollution is organized.

So, the water factor becomes important in the occurrence of infectious diseases under the following conditions:

1) pathogens with secretions of patients and bacillus carriers (both people and animals) enter the water;

2) pathogens retain their viability and ability to cause disease in water;

3) infected water enters the human body (through the digestive tract, external mucous membranes, microdamaged skin).

Infectious patients, as a rule, are hospitalized in infectious disease hospitals, where conditions are created for the disinfection of their secretions, as a result of which they should not be sources of infectious diseases during this period. They can infect the environment, including water, in the last days of the incubation period, when there are no manifestations of the disease yet, but the microbes in the body multiply intensively and are released.

Bacillus carriers are of particular danger - those who have had an infection. So, after suffering from typhoid fever, the ill person continues to excrete pathogens of this disease with feces and urine. In the first weeks after recovery, the release of typhoid microbes is observed in almost every second of those who have been ill (acute carriage). Over time, the number of carriers decreases and after three months it is reduced to 3--3.5% of the number of those who have been ill.

However, some people who have had typhoid fever may remain carriers for many months or even years (chronic carriers). Chronic carriers of typhoid fever have often been the source of major outbreaks of this disease. Acute and chronic carriage is observed in dysentery and other waterborne infections.

Chronic bacillus carriers are epidemiologically very dangerous for others because very often the carriage of the name of even virulent (resistant, with an increased ability to infect) pathogens does not affect their condition (i.e., goes unnoticed) and can only be established by repeated bacteriological studies .

There are also so-called healthy bacillus carriers. They are more often observed among persons who are in close contact with patients. Such bacillary carriage, as a rule, is short-lived, but it poses a great danger to others with its secretions. Therefore, the sanitary-epidemiological stations take into account all those who have recovered from infectious diseases, especially intestinal ones, and periodically check them for the carriage of bacteria. Persons who have had intestinal infections are not allowed to work in canteens, kitchens, food warehouses, and in the water supply system until they are fully recovered.

The World Health Organization (WHO) estimates that 80% of all diseases on earth are caused by contaminated water or a lack of basic hygiene.

2. Waterborne diseases

Many infectious diseases are transmitted through water: typhoid fever, dysentery, cholera, etc. An infection is the interaction of pathogenic microorganisms with other organisms under certain environmental conditions, which may result in an infectious disease. Pathogenicity is the potential ability of certain types of microorganisms to cause an infectious process. Pathogenic microbes are characterized by specificity, i.e. each microbe is capable of causing a specific infectious process. However, the possibility of occurrence and the nature of the development of the process, its severity, duration, outcome largely depend not so much on the microbe as on the degree of reactivity and resistance of the human or animal organism.

Pathogenic microbes can be in the body of a healthy person without causing the development of the disease. It has been proven that malnutrition, exposure to cold, alcohol, physical overwork, etc. contribute to the development of an infectious disease. Many pathogenic microorganisms produce enzymes that can destroy tissues and cells in the body. As a result, the permeability of microorganisms to the attacked organism increases.

The most important feature of pathogenic microbes is their toxicity. Distinguish between exotoxins and endotoxins. Exotoxins are poisons that readily diffuse into the environment. Endotoxins are firmly bound to the body of the microbial cell and are released only after it dies. The action of exotoxins is specific, i.e. they affect certain organs and tissues. For example, tetanus exotoxin causes damage to the nervous system, as a result of which the patient experiences muscle spasm; diphtheria affects the cardiovascular system, adrenal glands. If microbial exotoxins, being very strong poisons, have a detrimental effect on the body already in very small doses, then endotoxins are less toxic, do not have strict specificity, and cause general signs of poisoning in the body: headache, weakness, shortness of breath. Endotoxins are composed of polysaccharides and lipoproteins, and exotoxins are of a protein nature.

Infectious diseases differ from non-infectious diseases not only in their origin, but also in their course and clinical signs. There are the following periods of the course of the infectious process: incubation (hidden); period of precursors (prodromal); the period of the highest development of the disease (acme period); The outcome of the disease is recovery, transition to a chronic state, death.

An epidemic (a mass disease of people) occurs when there is an epidemic chain consisting of three links: the source of the infection, the ways of transmission of the infection, and the susceptibility of the population to this disease. The source of infection can be a sick person, animal or bacillus carriers. A bacillus carrier is a healthy organism, to which microbes do not cause harm, but, developing in it, are released into the external environment. Infectious diseases are transmitted in different ways: through food, air, insects, contact with the patient, including through water. This happens when drinking, bathing, washing dishes, vegetables, fruits, etc. The development of the epidemic depends on the susceptibility of the population and animals to this type of disease. Improving the living conditions of people, their accuracy, the implementation of preventive measures, the identification of bacillus carriers - all this limits the possibility of spreading diseases.

A wide variety of microbes can accidentally appear in water, but they can live in it for a long time, as numerous studies by scientists have shown, only causing cholera, typhoid fever, dysentery and other gastrointestinal diseases. The duration of their preservation in water is different. Cholera pathogens can survive in water from several days to several months. Dysentery sticks can stay in tap water for up to 27 days. The causative agents of typhoid fever remain viable in water for up to three months. Especially often the transmission of acute intestinal infections is observed when drinking contaminated water, but infection is also possible when using water for household needs.

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