INTRODUCTION OF INFECTIOUS DISEASES

Nowadays there are about 2,500 well-known microorganisms that cause infectious diseases. About 300 nosological forms have been distinctly described ("nosos" means "disease" in Greek). According to the international classification the infectious diseases relate to 13 classes and 975 rubrics. They constitute up to 60-70 % of the total morbidity. In polyclinics 4-6 patients out of 10 suffer from infectious diseases. The responsibility for the exposure of the infectious morbidity is taken by the physicians of the "first line" - therapeutists, surgeons, gynecologists and other specialists. Now it is distinctly ascertained that the infectious agents are the basic or leading ethiological factor of the different branches of the medical science.

Such fields of the internal diseases as rheumatology, pulmonology or hepatology cannot be conceived without taking into consideration the infectious factor. The infectious factor often determines the outcome of the surgery. The gynecological, urological and eye diseases cannot be treated without considering it. The association of the viral hepatitis  and C with the primary liver cancer is undoubted, there is a certain connection between the cancer of the cervix of the uterus and the virus of the herpes simplex, leucosis and Bercet's lymphosarcoma. The significance of the infections agents in bronchial asthma, arthritis, meningoencephalitis is undoubted.

Besides these many new earlier unknown discuses have appeared. Only during the last years such infections diseases as HIV, Legionnaires disease, cryptosporidiosis, SARS, hemorrhagic fevers, caused by Marburg or Ebola virus, hantavirus and others have appeared, they are responsible for the development of the ulcer disease of the stomach, pneumonia, meningoencephalitis, cutaneous diseases, lymphoadenopathy, heart and vessels diseases. Many researchers think that the world is standing on the verge of the T-cell leucosis epidemic, which is already widely spread in Japan and in some regions of Latin America. That is why a physician of any speciality will more or less often encounter with the infectious pathology.

The origin of the infectious diseases dates back from the ancient times. The old archives that contain the man's first descriptions of his thoughts with the help of signs tell us that he already suffered from such diseases as leprosy, hydrophobia, malaria, trachoma, fungous, helmintic and some other diseases.

Although the infectious diseases exist as long as life itself, their studying started comparatively not long ago. It is one of the youngest branches of science.

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The scientific history of the infectious diseases started at the end of the 19th century when the term "infectious diseases" was introduced, and it was determined that they were caused by the microorganisms i.e. the organisms that could be found only with the help of a microscope.

The common feature of the majority of the infectious diseases is the possibility of transmission from the affected organism to a healthy one, and the ability of massive (epidemic) spreading. During the study of the infectious diseases the terms "infection" and "infectious process" are usually used. They both originate from the Latin words - "infectio" - "pollution", "contamination" and "infecio" - "to pollute". At the modern level of the science development it is impossible to give an exhaustive definition of the terms "infection" and "infectious process" which would open all the sides of this conception. The term "infection" means the penetration of a microorganism into another organism and their following interaction under various conditions connected both with the microbe itself and the qualities of the organism which receives it at the various stages of the development of the organic world.

The term "infectious process" means the totality of the physiological, defensive and pathologic reactions, which appear under the certain conditions of the environment as an answer to the affection of the pathogenic microorganisms.

An infectious disease is the extreme stage of the infectious process development, which manifests in different signs and changes of the biological, chemical and epidemiological order.

According to all of these definitions it is obvious that the term "infection" cannot be identified with the "intectious process". The contents which we put into the term "infectious process" does not let us make a complete image of the infection as a general biological phenomenon. The concept "infection" is much wider as infection is common to all the beings. The infectious process includes the patterns common to the complicated organisms. The term "infectious process" is used to identify all the dynamics of the pathologic changes connected with the infection irrespective of the fact that they develop into a special qualitative condition called an infectious disease or not.

The origin of the infectious diseases and their nature were discovered

owing to the brilliant success of bacteriology. That is why for a long period of

ime the infectious process was identified only with the activity of the

microorganism without any consideration of the physiological aspects of the

macroorganism.

Later when the scientists started to pay more attention to the study of pathogenesis i.e. the mechanism of the sickness processes development,, they advanced a thesis of the domination of the macroorganism in the infectious process. It was a second mistake as it is impossible to separate something that is by the nature closely connected and can be understood only in correlation. Besides, the pathological process also has to be examined under the influence of

Introduction of infectious diseases 7

the environment. So if the disease develops as a result of the violation of this certain form of the organism's adaptation to the environment at the change of its conditions, then the infectious disease develops as the result of the influence of the part of environment which belongs to the living organisms. In other words, all the participants of the pathologic process are noted for the biological activity, functional mobility and the ability to develop.

The penetration of a certain number of microorganisms into the macroorganism is necessary for the infectious disease to develop. Besides, it has to be of a certain quality i.e. pathogenicity and virulence. However, the development of the pathological process depends on the general condition of the macroorganism and its immune status. In case of the weak immune status the pathologic process develops rapidly and the disease takes a severe course, in case of the comparatively strong immune status the disease takes a mild course or may not develop at all. Spreading of the disease and its severity depends on the environment - both on the geographical position (in the tropics - overheating, in cold countries — supercooling), and on the social sphere (a luxury villa and overcrowded facilities). All these processes can be expressed in the formula: the infectious disease is pro rate to the number and quality of the microbe (pathogenecity, virulence) and invasively to the immune status and the environment. Each of the mentioned factors is variable and they should be considered as dynamically developing with the changing of the cause and effect.

Comparing an infectious disease with a non-infectious one we can point out their mutual signs - intoxication and functional disorders of the organs and systems, morphological changes and others. However, with all the similarities we should mention the peculiarities of the infection diseases. This is, first of all, the cyclical course with expressed periods (incubative, prodromal, high point, fading healing). The second peculiarity is that the pathogen that caused the disease as a living agent has its own "interests" - it lives,multiplies as it tries to preserve its species - at the same time it adjusts, changes or remains in its constancy - the death of the macroorganism is not "profitable" for it as the pathogen can die with it as well. The third peculiarity is that the affected organism can become a source of infection for healthy people. The common feature of the majority of the infectious diseases is the possibility of transmission from the affected organism to healthy one and the ability of massive (epidemic) spreading. The fourth peculiarity consists of the immune processes which make the organism insensible to the later affections in case of the same etiologic factor.

Different interrelations occur when organisms contact with one another, it happens in nature all the time. To understand the infectious diseases we should mention the basic types of such interrelations.

1. The meeting and contact of the organisms do not have any consequences, any reaction. No symbiotic relations appear after it. In such cases we talk about species inherited immunity. For example, a human immunity to the horned livestock's plague, to the hemorrhage septicemia of cats and others.

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2. The meeting of the organisms results in the symbiotic commonwealth (in Greek „symbiosis" means state of living together). There may be no reaction at all on the part of both partners, the condition called saprophytosis („saprobe" means microorganism that lives in the dead organic remains) appears. Some researchers consider symbiosis to be any form of living together between the representatives of different species. To this symbiosis they refer:

a) synoikia (Greek) - neutral living together during which one species uses the other one as a place to live without harming it;

b) mutualism - the symbiosis that is profitable for both organisms;

e) commensalism (Lat. "com" - with, "mensa" - table) also (French -"commensa" - dependent) interrelation when one organism gets a benefit from the other without harming it;

d) parasitism - a microorganism feeds with the saps or tissues of the master harming it. Most of the infectious diseases belong to this kind of symbiosis.

Analyzing the pathogenic processes scientists divide the infectious diseases into endogenous and exogenous ones. The endogenous diseases or autoinfections develop from their own microflora which is situated on the skin, respiratory and alimentary tracts, conjunctive, genital tracts. Because of the disorder of the regulatory processes which provide the physiologic symbiotic balance, there develop local, widely spread or even general infectious processes. Such microorganisms are called conditionally pathogenic or half-parasites.

The diseases caused by the penetration of the microorganisms from the environment and to which a macroorganism is not resistant are called exogenous infectious diseases.

Such division is pretty relevant and only relatively right. Sometimes the endogenous infectious disease becomes dangerous to the others because of itself and because the symbionit acquires new biological qualities.

If the infectious disease is caused by one species of microorganism it is called simple. If two or more microbe agents participate in the disease,then we talk about mixed-infection. Joining one infection to the other may affect the infectious process in different directions sometimes intensifying it, sometimes decreasing its activity and manifestations. So while studying the infectious pathology we should consider not only the pathogen itself but their associations. Salmonella infection especially bent to join other infectious diseases and start the secondary pathological process, this phenomena is called nosoparasitism (in Greek "nosos" - disease).

The growing number of the diseases caused by the conditionally-pathogenic pathogens is mostly connected with the changed reactivity of the organism and especially immune response which as a rule in such cases forms very slowly and is not valuable. The autoimmune processes activate and take a leading role in pathogenesis and clinical manifestations.

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Many conditionally pathogenic as new discovered microorganisms are characterized with intracellular localization of the pathogens. Such infections can cause widely spread pathological disorders and they are more difficult with their diagnosis and treatment.

An immune system is one of the major targets of the affection of the environment negative factors according to the modern conception. There are six basic factors:

Human demographics and behavior. The important factors in changing human demographics include increases in the number of susceptible persons, the use of day care and immigration. A number of factors cause a rise in number of susceptible persons and the greater the population percentage that is susceptible to the infectious diseases, the greater is the potential for the disease transmission. In many countries in the developed world the number of seniors is growing. Since aging is associated with an increased susceptibility to the infectious diseases, the potential for the disease transmission is also increasing in these countries. In the USA, the percentage of the population over 65 years was about 4 % in 1900 and will reach almost 25 % in 2040. Certain underlying diseases also place more patients at risk for various infectious diseases, and these have also increased. For example, the reported incidence of diabetes mellitus in the USA increased from 0.5 % of the nation's population in 1935 to over 3 % in 1995. It is estimated that there are actually 16 million persons with diabetes in the USA, so the true incidence of this disease may be greater than 5 % of the population. The rates for many malignancies are also increasing, and these patients have increased susceptibility to infectious diseases from the disease process, during chemotherapy and, in some cases, lifelong even after the cure. Some of the most highly susceptible patients are those receiving immunosuppressive therapy following organ transplantation. Almost 20,000 organ transplants were performed in the USA in 1995. Worldwide the greatest factor increasing susceptibility may be the spread of HIV, which has led to millions of persons at increased risk for a variety of infectious diseases.

Such social changes as the increased use of day care also affect the emergence of infectious diseases. The increasing frequency of both parents working outside home or of single parent families led to a greater use of day care. The combination of susceptible children, inadequate hygiene, frequent infections, and frequent antimicrobial use is the perfect setting for the emergence of antimicrobial resistance. Thus, it is no surprise that day care attendance has been an important factor associated with the emergence of penicillin-resistant Streptococcus pneumoniae. A recent study demonstrated a 4-fold greater relative risk for colonization with a high-level penicillin-resistant Streptococcus pnenmoniae among children attending day care.

The increase of immigration and changing the patterns of immigration also contribute to the emergence of the infectious diseases. Between 1984 and 1992,

Date: 2014-12-21; view: 1244