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GENERAL PRINCIPLES OF INFECTIOUS DISEASES Department of Infectious Diseases, t he Third Affiliated Hospital Li Gang ( 李刚) 2009.2.

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GENERAL PRINCIPLESOF INFECTIOUS DISEASESDepartment of Infectious Diseases, the Third Affiliated HospitalLi Gang (李刚)2009.2


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Introduction·Definition of infectious diseases and communicable diseases. · Distinction between infectious diseases and communicable diseases.


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Definition:

1. Infectious disease: any infection caused by microbes or parasites.

2. Communicable disease: infection transmitted from persons or animals to other persons.


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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)



The concept of infection the course of struggle between pathogens and human or animal bodies host l.jpg
The concept of infection The course of struggle between pathogens and human or animal bodies (host).


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Pathogens:(microbes, parasites)

Prion; virus; chlamydia; rickettsia; bacteria; fungus; spirochete.

Protozoa; helminth.


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Emerging pathogens and infectious diseases

1977 Hantaan virus

1977 Ebola virus

1982 E coli O157:H7

1983 HIV

1986 CJD

1988 HEV

1989 HCV

1992 Vibrio cholerae O139 strain

1997 H5N1

2003 SARS coronavirus



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⑴ Commensal infection: Pathogens live in the host but don’t induce pathologic changes.


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⑵ Opportunistic infection:Pathogens within the host can induce pathologic changes if host immunity is suppressed by some factors.


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⑶ Pathogenic infection: According to the severity of the pathologic changes, several degrees in clinical manifestation from mild, moderate to severe will occur.


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Infection status:

Primary infection

re-infection

co-infection

super infection

secondary infection




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1. Elimination: following results. pathogens were excluded out by host nonspecific or specific immunity. Such as Candida albicans Escherichia coli


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2. Covert (subclinical) infection: following results.■ Most frequently occurs in healthy individuals. ■ The outcomes will be: A. Immunity acquired. B. Carrier state: healthy carriers.


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3. Overt (clinical) infection: following results. The outcomes will be: A. Recovery. B. Chronic carrier.


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4. Carrier state: following results. Definition of different types of carriers: . incubation carrier . acute carrier . convalescent carrier . chronic carrier


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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.


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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.


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The Role of Immune Response in Infection Process: following results.Differentiation between protective immunity and allergy. . Protective immunity: beneficial . Allergy(anaphylactic reaction): harmful


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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.


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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.


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Pathogenic Mechanisms of Infectious Diseases following results.The occurrence and natural course of infections can be divided into three stages:


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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.


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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.


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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.


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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.


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Mechanism of Tissue Damages following results.3. Immunopathogenesis: Immunosuppression, T-cell destruction, immune complexes, antibody-mediated cytotoxicities.



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1. Fever(pyrexia): following results. Exogenous and endogenous pyrogens.. Exogenous pyrogens: virus etc. . Endogenous pyrogens: IL-1, TNF, IL-6, interferon etc.


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2. following results. Metabolismchanges:(1) Protein: higher proteins catabolism. “acute” proteins (C-reactive protein, sign of acute inflammation). (2) Carbohydrate: acceleration of glucolysis.


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2. following results. Metabolismchanges:(3) Water and electrolytes: dehydration, hypokalemia.(4) Endocrine disturbances: higher anabolism, stress, hyper-corticosteroidemia.



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Epidemiological Process (course): Influencing Factors Definition: case occur, spread. The essential elements of epidemiological process include:


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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.


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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.


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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.


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3. Population susceptibility: Influencing Factors

Proportion of susceptibles.


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Factors Influencing Influencing FactorsEpidemiological Process


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1. Natural factors: Influencing FactorsClimatic and geographic factors.. Climatic: season, rain, humidity.. Geographic: endemicity.


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2. Social factors: Influencing Factors social system, social-economic condition, cultural background.



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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.


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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.


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2. Common symptoms and Influencing Factors signs.


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Influencing FactorsFever(pyrexia) :Courses:A. Effervescence: early stage. B. Fastigium: full-blown stage.C. Defervescence: improvement stage


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Forms: Influencing FactorsA. Sustained fever:Difference of body temperature less than 1℃ within 24 hours, over 39℃. e.g. Second week of typhoid.


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1 Influencing Factors

2

3

4

5

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B. Remittent fever: Influencing FactorsChange of body temperature more than 1 ℃ within 24 hours, the base line higher than normal. e.g. Septicemia.


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C. Intermittent fever: Influencing FactorsFluctuation between normal temperature and high fever within 24 hours. e.g. Malaria.


D relapsing fever fever lasting 5 7 days with relapse after several days e g relapsing fever l.jpg

D. Relapsing fever: Influencing Factors Fever lasting 5~7 days with relapse after several days. e.g. Relapsing fever.


E undulent fever fever lasting several weeks with relapse after several weeks e g brucellosis l.jpg

E. Influencing FactorsUndulent fever: Fever lasting several weeks with relapse after several weeks. e.g. brucellosis.


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波状热 Influencing Factors


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F. Irregular fever: Influencing Factors Curve of body temperature is irregular. e.g. Brucellosis, septicemia.


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G. Saddle-type fever: Influencing Factors Fever for several days, then with normal temperature for 1 day, and then relapse. e.g. Dengue.


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Influencing FactorsSkin rash or eruption:Note appearance type, day of the disease, and distribution.


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A. Exanthem: Influencing FactorsRash on skin surface. e.g. chickenpox.B. Enanthem:Rash on mucous membrane. e.g. Koplik spots in measles.


A maculopapular rash e g macula and papule maculopapule in measles rose spots in typhoid fever l.jpg
a Influencing Factors. Maculopapular rash: e.g. Macula and papule (Maculopapule) in measles; rose spots in typhoid fever.


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b. Petechiae: Influencing Factorssubcutaneous hemorrhages or ecchymosis. e.g. septicemia, typhus, hemorrhagic fever with renal syndrome.


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c. Vesiculo-pustule rash: Influencing FactorsVesicles and pustules in skin and mucous membrane. e.g. Varicella(chickenpox), herpes zoster, smallpox.


D urticaria seen in serum sickness parasitic diseases drug hypersensitivity etc l.jpg
d. Urticaria: Influencing Factors Seen in serum sickness, parasitic diseases, drug hypersensitivity, etc.


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(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.


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B. Influencing FactorsReticulo-endothelial system reactions: hepatomegaly, splenomegaly, lymphadenopathy.


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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).



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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.


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Pathognomonic signs Influencing Factors

  • Measles: Koplik spots

  • Mumps: swelling of parotid gland

  • Scrub typhus: eschar

  • Leptospirosis: myalgia, calf muscle

  • Typhoid: rose spots

  • Cysticercosis: subcutaneous nodules

  • Hepatoencephalopathy: flapping tremor

  • Schistosomiasis: urticaria

  • Shigellosis: mucus-pus-bloody stool

  • Amebic dysentery: strawberry jam-like stool

  • Rabies: hydrophobia



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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.


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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.


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Leukocytosis: Influencing Factors

Infection with virus:

epidemic hemorrhagic fever,

Japanese B encephalitis,

infectious mononucleosis.

Infection with bacteria, etc.


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(2) Detection and isolation of Influencing Factors pathogens:A. Adequate collection and transportation of specimens.


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B. Influencing FactorsDirect examination: macroscopy: e.g. Ascaris lumbricoides, hook worm, Enterobius vermicularis, etc.microscopy:e.g.Plasmodium, Cryptococcus neoformans,Mycobacterium tuberculosis


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C. Influencing FactorsCulture by artificial media or tissue culture. Media culture:Entamoeba histolytica, Shigella, Salmonella, etc. Tissue culture:dengue virus, poliovirus, etc.


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D. Influencing FactorsAnimal inoculation. Intraperitoneal inoculation: Rickettsia tsutsugamushi.Intracerebral inoculation:encephalitis virus.


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E. Specific antigen detection: Influencing Factors Methods: agglutination test, ELISA, EIA, FAT, RIA, flow cytometry, etc.


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F. Molecular biologic assay: Influencing Factors Using isotope or non-isotope probes; Polymerase chain reaction (PCR).Mycobacterium tuberculosis, hepatitis C virus, etc.


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(3) Detection of specific Influencing Factors antibodies: By means of : ELISA, RIA, etc. IgM, IgG antibodies.


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(4) Others: Influencing FactorsT-cell subset assay: e.g. for AIDS.


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Skin test: Influencing Factorse.g. for tuberculosis, cysticercosis.


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Fibro-optic endoscopy: Influencing Factors e.g. for esophageal varices.


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Imaging (X-ray, ultrasound, Influencing Factors CT, MR):e.g. for amebic liver abscess.


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Biopsy: Influencing Factors e.g. for chronic hepatitis.



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Principles of therapy Influencing Factors


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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.


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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.



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1. Measures against the Influencing Factors source of infection:


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Influencing FactorsReport of cases: According to the Law for Controlling Infectious Diseases issued by the central government.


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Three kinds of case report: Influencing FactorsKind A: plague, cholera, smallpox. <6hs.Kind B: AIDS, hepatitis, etc. <12hs.Kind C: influenza, mumps, etc.<48hs.


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Influencing FactorsIsolation of patients: until the patient becomes non-infectious.


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(3) Influencing FactorsQuarantine of contacts: until the incubation period of the infectious disease is over.


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Influencing FactorsIdentification and treatment of carriers.


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Influencing FactorsControl of infected animals: Eradication or therapy.


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2. I Influencing Factorsnterrupt (Block) the routes of transmission:


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Influencing FactorsGeneral hygienic measures: Clean drinking water supply, food hygiene, correct sewage disposal.


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Influencing FactorsDisinfection and eradication of insect vectors.


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Influencing FactorsIntervention of parasite life cycles. e.g. eradication of snails (Oncomelania) in endemic area of schistosomiasis.


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3. Protection of the susceptible Influencing Factors persons:


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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.


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Influencing FactorsProtection from environmental factors: e.g. mosquitoes bites, skin penetration byLeptospira andhookworm larvae.


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Influencing FactorsChemo-prophylaxis: artesunate against malaria


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