GENERAL PRINCIPLES OF INFECTIOUS DISEASES Department of Infectious Diseases, t he Third Affiliated Hospital Li Gang ( 李刚） 2009.2.
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Introduction·Definition of infectious diseases and communicable diseases. · Distinction between infectious diseases and communicable diseases.
1. Infectious disease: any infection caused by microbes or parasites.
2. Communicable disease: infection transmitted from persons or animals to other persons.
The goal of studying infectious disease:1. To study etiology, epidemiology, pathogenesis, clinical manifestations, treatment and prevention of infectious diseases. 2. To control and eliminate these diseases. (occurrence, spreading, prevention)
Prion; virus; chlamydia; rickettsia; bacteria; fungus; spirochete.
1977 Hantaan virus
1977 Ebola virus
1982 E coli O157：H7
1992 Vibrio cholerae O139 strain
2003 SARS coronavirus
⑶ Pathogenic infection: According to the severity of the pathologic changes, several degrees in clinical manifestation from mild, moderate to severe will occur.
1. Elimination: following results. pathogens were excluded out by host nonspecific or specific immunity. Such as Candida albicans Escherichia coli
2. Covert (subclinical) infection: following results.￭ Most frequently occurs in healthy individuals. ￭ The outcomes will be: A. Immunity acquired. B. Carrier state: healthy carriers.
4. Carrier state: following results. Definition of different types of carriers: . incubation carrier . acute carrier . convalescent carrier . chronic carrier
5. Latent infection: following results.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.
The Role of Pathogens in the Infection Process: following results.⑴ Invasiveness: adhesion, penetration ability. ⑵ Virulence: toxins, enzymes, and histolytic ability.⑶ Infection dose: minimal dose that can cause an infection.⑷Variability: change in structure of the pathogen to evade from host immunity.
The Role of Immune Response in Infection Process: following results.Differentiation between protective immunity and allergy. . Protective immunity: beneficial . Allergy(anaphylactic reaction): harmful
⑴ following results.Nonspecific immunity:A. Natural barriers:external (skin, mucous membrane, cilia), internal (blood-brain barrier).B. Phagocytosis:macrophages, monocytes, and granulocytes.C. Humoral factors: complements, interferons, lysozyme, cytokines.
⑵ following results.Specific immunity: Immune respond to specific recognizable antigens. A. Cell-mediated immunity: Important in intracellular infections by viruses, fungi, protozoa and certain bacteria.B. Humoral immunity: Different kinds of antibodies (immune globulins) and their functions.
1. following results.Portal of entry:Each pathogen has its specific portal of entry.Such as: Mycobacterium tuberculosis, Meningococcus via breath tract. Shigella via digestive tract.
2. following results.Localization and Dissemination in the host:Specific for each pathogen.Such as: . Mumps virus in parotid gland. . Hepatitis C virus in the liver. . Shigella in the intestine.
3. Channels of excretion: following results. Important factor for host infectivity. As the source of infection. Such as: . Hepatitis A in the stool. . Hepatitis B in the blood. . Measles virus in expiratory air.
Mechanism of Tissue Damages following results.1. Direct invasion: Cytolysis, tissue necrosis, inflammation.2.The actions of toxins and cytokines: Resulting in septic shock, Disseminated intravascular coagulation, etc.
Mechanism of Tissue Damages following results.3. Immunopathogenesis: Immunosuppression, T-cell destruction, immune complexes, antibody-mediated cytotoxicities.
1. Fever(pyrexia): following results. Exogenous and endogenous pyrogens.. Exogenous pyrogens: virus etc. . Endogenous pyrogens: IL-1, TNF, IL-6, interferon etc.
2. following results. Metabolismchanges:(1) Protein: higher proteins catabolism. “acute” proteins (C-reactive protein, sign of acute inflammation). (2) Carbohydrate: acceleration of glucolysis.
2. following results. Metabolismchanges:(3) Water and electrolytes: dehydration, hypokalemia.(4) Endocrine disturbances: higher anabolism, stress, hyper-corticosteroidemia.
1. Sources of infection: Influencing FactorsDefinition. Human, animal.⑴ Patients: acute, chronic; typical, atypical(mild, severe).⑵ Subclinical infection:no symptoms. poliomyelitis.⑶ Carriers:chronic, typhoid, shigellosis.⑷ Infected animals:(natural source)rabies, plague.
2. Routes of transmission Influencing Factors⑴ Air, droplets, dusts. e.g. measles.⑵ Water, food, flies(fecal-oral infection).e.g. typhoid.⑶ Fingers, utensils(contact infection).e.g. shigellosis, influenza.
⑷ Arthropods. Influencing FactorsA. Biologic:intermediate hosts. e.g. mosquitoes in malaria, chiggers in scrub typhus. B. Mechanical:passive transfer. e.g. flies in amebiasis.
3. Population susceptibility: Influencing Factors
Proportion of susceptibles.
Basic characteristics: Influencing Factors(1) Pathogens.(2) Infectivity. (3) Epidemiological features: age, sex, season; imported or endemic; sporadic, epidemic, pandemic, outbreaks.(4) Post-infection immunity.
2. Clinical Characteristics: Influencing Factors(1) Development stage:A.Incubation period.B.Prodromal period.C.Symptomatic period. Apparent clinical manifestations.D.Convalescent period.E. Recrudescence or relapse.F.Sequelae.
1 Influencing Factors
波状热 Influencing Factors
(3) Toxemic symptoms: Influencing FactorsA. General presentations: malaise; headache; anorexia; pain in muscles, joints and bones; disturbance in consciousness; meningeal irritation; septic shock; liver and kidney failure, etc.
4. Clinical forms: Influencing Factors(1) development: Acute, subacute and chronic forms. (2) forms of clinical manifestation: mild, moderate (typical) or severe forms of the disease. ambulatory form in typhoid (without symptom and signs).
1. Clinical manifestations Influencing Factors(1) Mode of onset(2) Type of fever(3) Accompanying symptoms:headache, myalgia, arthralgia etc.(4) Signs:Consciousness, jaundice, skin rash, buccal membrane, Koplik spot, eschar, subcutaneous hemorrhage, liver, spleen, lymph nodes.
Characteristic sign of scrub typhus Influencing Factors
2. Epidemiological Data: Influencing Factors(1) History of contact with similar cases.(2) Occupation, living environment and life style.(3) History of vaccination.(4) History of transfusion of blood or blood products.
3. Laboratory Examinations: Influencing Factors(1) Routine examinations: blood, urine, stool. Leukocytosis, leukopenia, eosinopenia, eosinophilia. Biochemical analysis of the blood for liver functions and kidney functions, etc.
Infection with virus:
epidemic hemorrhagic fever,
Japanese B encephalitis,
Infection with bacteria, etc.
B. Influencing FactorsDirect examination: macroscopy: e.g. Ascaris lumbricoides, hook worm, Enterobius vermicularis, etc.microscopy:e.g.Plasmodium, Cryptococcus neoformans,Mycobacterium tuberculosis
C. Influencing FactorsCulture by artificial media or tissue culture. Media culture:Entamoeba histolytica, Shigella, Salmonella, etc. Tissue culture:dengue virus, poliovirus, etc.
F. Molecular biologic assay: Influencing Factors Using isotope or non-isotope probes; Polymerase chain reaction (PCR).Mycobacterium tuberculosis, hepatitis C virus, etc.
1. Aim of treatment: Influencing Factors . Not only for alleviation of symptoms and signs, but also for isolation of patients to prevent propagation of infection to the community. . Comprehensive treatmentincludes drug therapy, nursing care and isolation. . Pay attention to both specific and symptomatic treatments.
2. Therapeutic methods: Influencing Factors⑴General and supportive treatment. ⑵ Etiologic (specific) treatment.⑶ Symptomatic treatment.⑷ Rehabilitation therapy for sequelae.⑸ Traditional Chinese medicine and acupuncture.
Three kinds of case report: Influencing FactorsKind A: plague, cholera, smallpox. <6hs.Kind B: AIDS, hepatitis, etc. <12hs.Kind C: influenza, mumps, etc.<48hs.
⑴ Influencing FactorsImmunological prophylaxis: . Active (vaccination): intracutaneous inoculation with smallpox vaccine. subcutaneous inoculation with hepatitis B vaccine. . passive (immunoglobulins): intramuscular injection with antibodies against tetanus bacillus.