MEDICAL FACULTY
Division for Foreign Students with Instruction Conducted in English
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Department of Microbiology, Virology and Immunology
GENERAL MICROBIOLOGY
THEORETICAL & LABORATORY MANUAL
PART III. APPLIED INFECTOLOGY & IMMUNOLOGY
E. V. Budanova and N. V. Khoroshko
Edited by: Academician V.V. Zverev
Special English edited by: Associate Professor I. Yu. Markovina.
Computer Illustrations by: A.V. Budanov
M O S C O W - 2008
Recommended reading:
1. Topical lectures
2. Textbook 1: Mechanisms of Microbial Disease/edited by Moselio Schaechter, Gerald Medoff, Barry I. Eisenstein. - 2nd ed.
3. Textbook 2: Medical Microbiology & Immunology. Examination and Board Review./W. Levinson, E. Jawetz.-5th ed.
4. Manual (Part 3)
SECTION 3: INFECTION and IMMUNITY
The objectives. The students should know: the properties of the pathogenic microbes, their causative role in the occurrence and development of infectious process; host defence mechanisms; the structure and functions of the immune system, kinds of immune response of the human organism; the mechanisms of diagnostic immunological tests; modern principles of vaccination and serotherapy of infectious diseases.
LESSON 11
INFECTION. INNATE IMMUNITY. NONSPECIFIC FACTORS of HOST DEFENCE
Prelab conference. Topics for discussion:
1. Infection. Infectious process. Infectious disease.
2. Types of infection.
3. Generalized infections. Bacteriemia. Sepsis. Toxemia.
4. Pathogenicity and virulence of microbes. Virulence factors of bacteria.
5. Exotoxins and endotoxins of bacteria.
6. Determination of microbial virulence.
7. Innate immunity. The nonspecific factors of host defence.
8. Phagocytosis and phagocytes. The mechanism and stages of phagocytosis. The incomplete phagocytosis.
Infection (or infectious process) – involves interactions between the susceptiblemacroorganism (host) and the infecting microbe under specific environmental conditions. This includes the lodgment and multiplication of a parasite in or on the tissues of a host.
With the exception of diseases caused by the inoculation of microbes directly into the bloodstream or other internal tissues, an infectious disease is initiated by adhesion and colonization, the establishment of microbes on the skin or mucous membranes. Microbial colonization of a body site may result in one of several outcomes.
The outcome of exposure to microorganisms depends on a dynamic balance between the relative abilities of the host to resist infection and the invader to cause disease. In the absence of clinical treatment, several possible consequences follow a person's exposure to pathogenic microorganisms:
• No infection. Disease fails to develop, and no organisms are shed.
• Inapparent (subclinical) infection. No clinical symptoms develop; a carrier state may be established and may persist. (Carriers are apparently healthy persons who shed pathogens and can therefore transmit disease.)
• Mild acute symptomatic disease. Symptoms develop after a brief incubation period and then disappear quickly.
• Severe acute disease. Debilitating or fatal symptoms quickly develop.
• Chronic infectious disease. Symptoms persist for months or years.
• Latent infection. Pathogen remains dormant in the host following apparent recovery; recurrences are common.
Many explanations account for this array of results. One factor is a person's susceptibility to a particular disease. Another is the number of cells to which the host is exposed—the more microorganisms introduced into the body, the more likely the host is to develop infectious disease. In addition, the nature of the pathogens, how they are introduced into the host, and the host response to the pathogens determine pathogenesis (sequence of events and mechanism of tissue injury) and clinical manifestations (symptoms of disease) following exposure.
It is necessary to distinguish between the term “infection” and “infectious disease.” Infection often (but not always) has no detrimental effects on the host. Infectious disease occurs only if the microbe or its growth by-products directly injure the infected person or elicit a host reaction that damages tissues. Infection is therefore distinct from disease, because infectious disease is a rare consequence of infection that produces injury or damage to the body.
Usually there are some stages in the development of infectious disease:
1. Incubation period (the time between exposure to the agent and the onset of the first clinical symptoms).
2. Prodromal period ( theearliest stage of a developing disease that is characterizedwith the first nonspecific clinical symptoms).