【正文】 Kinds of infections 20 ? Commensalism Pathogens live in the host but don’t induce pathologic changes. Escherichia coli in the colon EpsteinBarr virus 21 ? Opportunistic infection: Pathogens within the host can induce pathologic changes if host immunity is suppressed by some factors. Cryptococcus neoformans Cytomegalovirus Candida albicans 22 ? Primary infection: measles, chicken box ? Repeated infection: malaria, schistosomiasis, ancylostomiasis ? Mixed infection: rare ? Superinfection: HBV overlap HEV ? Secondary infection: HBV following bacilli 23 ? Eliminate pathogen ? inapparent/subclinical infection ? apparent/clinical infection ? Carrier status ? Latent infection Infections status（ infection spectrum） Entrance and colonization of pathogens will lead to the following results 24 ㈠ Elimination: pathogens were excluded out by host nonspecific or specific immunity. Such as: Candida albicans Hepatitis A virus 25 ㈡ inapparent/subclinical infection: most frequently occurs in healthy individuals. The outes will be: A. Immunity acquired. HAV B. Carrier state: healthy carriers. HBV 26 ㈢ apparent/clinical infection : The outes will be: A. Recovery. Shigella B. Chronic carrier. Salmonella typhi 27 ㈣ Carrier state: Definition of different types of carriers: . incubation carrier . acute carrier . convalescent carrier . chronic carrier 28 ㈤ Latent infection: After infection, pathogens remain latent inside the body. Develop clinical manifestations when the host immunity has been impaired. Pathogens usually will not be excreted by the host during period of latency. Herpes simplex 29 ? The infection status may change each other in some conditions. Latent infection Apparent Carrier status Inapparent eliminate frequency/ratio 30 三、 Role of Pathogens in Infection Process: ⑴ Invasiveness: adhesion, peration ability. Shigella ⑵ Virulence: toxins, enzymes, and histolytic ability. E. histolytica ⑶ Infection dose: minimal dose that can cause an infection. S. typhi ⑷ Variability: change in structure of the pathogen to evade from host immunity. Influenza virus 31 四、 The Role of Immune Response in Infection Process: Differentiation between protective immunity and allergy. . Protective immunity: beneficial . Allergy(anaphylactic reaction): harmful 32 ⑴ Nonspecific immunity: A. Natural barriers: external (skin, mucous membrane, cilia), internal (bloodbrain barrier). B. Phagocytosis: monocytes, macrophages, and granulocytes. C. Humoral factors: plements, lysozyme, interferons (α β γ), cytokines 33 ⑵ Specific immunity: Immune respond to specific recognizable antigens. A. Cellmediated immunity: Important in intracellular infections by viruses, fungi, protozoa and certain bacteria. B. Humoral immunity: Different kinds of antibodies (immune globulins, A D E G M) and their functions. 34 Pathogenic Mechanisms of Infectious Diseases 35 Establishment and development of infection process can be divided into three stages 1. Portal of entry: Each pathogen has its specific portal of entry. Mycobacterium tuberculosis, Meningococcus via breath tract. Shigella via digestive tract. 36 2. localization and Dissemination in the host: Specific for each pathogen. . Mumps virus in parotid gland. . Hepatit