CH 11. Interaction between Microbes and Humans

Transcription

1 CH 11 Interaction between Microbes and Humans

2 SLOs 1. Differentiate among the terms colonization, infection, and disease. 2. Enumerate the sites where normal biota is found in humans. 3. Discuss how the Human Microbiome Project is changing our understanding of normal biota. 4. Differentiate between a microbe s pathogenicity and its virulence. 5. Define opportunism and list examples of common opportunistic pathogens. 6. List the steps a microbe has to take to get to the point where it can cause disease. 7. List several portals of entry and exit. 8. Define infectious dose, and explain its role in establishing infection. 9. Describe three ways microbes cause tissue damage. 10. Compare and contrast major characteristics of endotoxins and exotoxins. 11. Provide a definition of virulence factors. 12. Draw a diagram of the stages of disease in a human. 13. Differentiate among various types of reservoirs, providing examples of each. 14. List several different modes of transmission of infectious agents. 15. Define healthcare-associated infection, and list the three most common types. 16. List Koch s postulates, and discuss when they might not be appropriate in establishing causation. 17. Summarize the goals of epidemiology, and differentiate it from traditional medical practice. 18. Explain what is meant by a diseases being notifiable or reportable, and provide examples. 19. Define incidence and prevalence, and explain the difference between them. 20. Discuss the three major types of epidemics, and identify the epidemic curve associated with each.

3 The Human Host - HMP In health: Dynamic equilibrium with microbes Launched by NIH in 2007 Mission: Generate resources and expertise needed to characterize the human microbiome and analyze its role in health and disease. Microbiome has much broader impact on our health than previously realized. Bioinformed Design

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5 HMP cont. Human cells: How many protein-encoding genes? Microbiota: 8 million protein encoding genes Microbes found in locations previously thought to be sterile. All healthy people harbor potentially dangerous pathogens in low numbers. The makeup of one s intestinal biota can influence overall health.

6 The Normal Microbiota (Flora) = resident flora. Acquisition was thought to start during passage through birth canal. Current thinking? Establishes permanent colonies on & inside body without producing disease. Protection of host via Microbial antagonism or Limited number of attachment sites Chemical or physiological environment created by resident biota is hostile to other microbes.

7 Location

8 Factors that weaken host defenses and increase susceptibility to infection? Name at least 5:

9 The Progress of an Infection: Vocabulary Pathology: Pathogen: Pathogenic agents have special properties that allow them to invade the human body or produce toxins. Pathogenicity: Virulence: and virulence factors True or 1 pathogens vs. pathogens Infection: invasion and growth of pathogens in the body Disease: Abnormal state in which the body is not functioning normally. i.e.: infectious agent overcomes body s defenses Etiology:

10 Step One: Becoming Established Portals of Entry Portals of entry Exogenous vs. endogenous agents Various portals of entry: Mucous membranes Conjunctiva Respiratory tract: Droplet inhalation of moisture and dust particles. Most common portal of entry. GI tract: food, water, contaminated fingers Genitourinary tract Skin Impenetrable for most microorganisms; possible to enter through hair follicles and sweat ducts. Parenteral Route Trauma (S. aureus, C. tetani) Arthropods (Y. pestis) Injections

11 Inoculum Size: Numbers of Invading Microbes ID 50 : LD 50 : Bacillus anthracis has more than one portal of entry Portal of Entry ID 50 Skin Inhalation Ingestion endospores 10,000 20,000 endospores 250,000 1,000,000 endospores -ID for rickettsia: a single cell. -ID for tuberculosis, giardiasis, and coccidioidomycosis: about 10 cells. -ID for gonorrhea: 1,000 cells. -ID for cholera is 1,000,000,000 cells.

12 Step Two: Becoming Established Attachment Adhesion or adherence Adhesins: surface projections on pathogen, mostly made of glycoproteins or lipoproteins. Adhere to complementary receptors on host cell. They can be part of: Fimbriae (also pili and flagella): e.g.e. coli Capsules : e.g. S. mutans Biofilms provide attachment and resistance to antimicrobial agents Spikes Mechanical devices on worms

13 Step Three: Becoming Established Surviving Host Defenses Phagocytes =? Antiphagocytic Factors: Capsules (and slime layers) avoid phagocytosis Leukocidins: kill phagocytes outright Some bacteria survive inside the phagocyte. Step Four: Causing Disease Three ways by which microorganisms cause damage to their hosts: Enzyme action Toxins (endotoxins and exotoxins) Excessive or inappropriate host defense

14 Enzymes

15 Toxins Exotoxins: proteins (Gram- and + bacteria can produce) Endotoxins: Gram- bacteria only. LPS, Lipid A part released upon cell death. Symptoms due to vigorous inflammation. Massive release endotoxic shock

16 Vocabulary related to Toxin Production Toxin: Substances that contribute to pathogenicity. Toxigenicity: Ability to produce a toxin. Toxemia: Toxoid: Antitoxin:

17 Exotoxins Summary Source: Gram + and Gram - Relation to microbe: Chemistry: By-products of growing cell Fever? Neutralized by antitoxin? LD 50 : No Small Circulate to site of activity. Affect body before immune response possible. Exotoxins with special action sites: Neuro-, entero-, and nephrotoxins, hemolysins.

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19 Superantigens Special type of Exotoxin Nonspecifically stimulate T-cells. Intense immune response due to release of cytokines. Fever, nausea, vomiting, diarrhea, shock, death. and

20 Representative Examples of Exotoxins Bacterial Species Exotoxin C. diphtheriae toxin S. pyogenes Membrane-disrupting erythrogenic toxin C. botulinum neurotoxin C. tetani neurotoxin V. cholerae enterotoxin S. aureus Superantigen

21 Endotoxins Bacterial cell death, antibiotics, and antibodies may cause the release of endotoxins. Pyrogen: Endotoxins cause fever by inducing the release of interleukin-1. Dramatic fall in blood pressure can lead to shock and death Fig 15.6

22 Endotoxin Summary Compare to Table 11.3 Source: Gram Relation to microbe: Present in LPS of outer membrane Chemistry: Fever? Neutralized by antitoxin? LD 50 : Yes Relatively large

23 Warning Signals of Disease Symptoms are subjective. Change in body function felt by patient as result of disease Signs are objecitve. Change that can be measured or observed. E.g.:? Syndrome: Group of signs and/or symptoms that accompany a disease Signs & Symptoms of Inflammation: 4 (5) cardinal signs:?

24 Signs of Infection in the Blood -Leukocytosis -Leukopenia -Difference between septicemia and Bacteremia? -asymptomatic, subclinical, or inapparent infections

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26 Step Five: Vacating the Host Portals of Exit Usually the same as the portal of entry, but some pathogens use a different route. Respiratory tract: Coughing and sneezing Gastrointestinal tract: Feces and saliva Genitourinary tract: Urine and vaginal secretions Skin Blood: Biting arthropods and needles or syringes Fig 11.6

27 Persistence of Microbes and Pathologic Conditions Latency: dormant state in certain chronic diseases - Viral latency: herpes simplex, herpes zoster, Epstein-Barr, hepatitis B, AIDS - Bacterial/protozoan latency: syphilis, typhoid fever, tuberculosis Sequelae: long-term or permanent damage to tissues or organs - Meningitis: deafness - Strep throat: rheumatic heart disease - Lyme disease: arthritis - Polio: paralysis

28 What Happens in Your Body Incubation period: Time interval between initial infection and 1 st appearance of signs and symptoms. Prodromal stage: Characterized by appearance of first mild signs and symptoms. Period of invasion (illness): Disease at its height: all disease signs and symptoms apparent. Signs and symptoms subside. Period of convalescence: Body returns to prediseased state, health is restored.

29 Reservoirs: Where Pathogens Persist Continual source of infectious agents Transmitter: Individual or object from which infection is acquired - Syphilis: reservoir and transmitter are the same - Hepatitis A: reservoir is a human, transmitter is food Human: people with disease or asymptomatic carriers may have inaparent infections or latent diseases Nonliving: Soil,... Animal: Pathogen for some other species lives and multiplies in reservoir. Zoonoses make up 70% of new emerging diseases worldwide

30 Reservoirs Compare to Table 11.5

31 Aquisition and Transmission of Disease How does disease behave in population? Communicable vs. Non-communicable vs. Contagious Transmission Patterns: Horizontal vs. vertical Direct: Close association between infected and susceptible host. Touch, droplet, parenteral Indirect: Spread via fomites and vehicle transmission. Vector transmission

32 Vectors Vector Transmission: Arthropods carry pathogens from one host to another. Mechanical vector vs. biological vector.

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34 Healthcare-Associated Infections Nosocomial Infections From % of all admitted patients, with an average of 5% 2 4 million cases a year, resulting in 90,000 deaths 8 million in additional days of hospitalization and an increased cost of $5 10 billion Factors tied to healthcare-associated infections: - Compromised patients - Lowered defenses permit normal biota to enter the body - Collection point for pathogens - Infections acquired directly or indirectly from fomites, medical equipment, other patients, medical personnel, visitors, air, and water

35 Fig 11.8

36 Healthcare processes that lead to healthcare-associated infections: Treatments using reusable instruments such as respirators and thermometers Indwelling devices such as catheters, prosthetic heart valves, grafts, drainage tubes, and tracheostomy tubes antimicrobial therapy selects for drug-resistant microbes

37 Common Causes of HAIs Coagulase-negative staphylococci Percentage of Total Infections Percentage Resistant to Antibiotics 15% 89% S. aureus 15% 80% Enterococcus 10% 4 71% Gram-negative rods 15 25% 3 32% C. difficile 13% Not reported

38 Koch s Postulates: Proof of Etiology of Infectious Diseases 1. The same pathogen must be present in every case of the disease 2. The pathogen must be isolated from the diseased host and grown in pure culture 3. The pathogen from the pure culture must cause the disease when it is inoculated into a healthy, susceptible lab animal 4. The pathogen must be isolated from the inoculated animal and must be shown to be the original microbe

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40 Exceptions to Koch s Postulates Modification of Koch s postulates were necessary 1. to establish disease etiology for viruses and bacteria, which cannot be grown on artificial media 2. Certain pathogens, such as HIV, cause disease in humans only or have a very narrow host range 3. Some diseases, e.g.: pneumonia and nephritis, may be caused by polymicrobial infections. 4. Some pathogens, such as S. pyogenes, cause different diseases in different hosts.

41 For each of the descriptions below, determine if it pertains to an exotoxin or an endotoxin. Toxic in minute amounts Causes systemic effects such as fever and inflammation Released by a cell via shedding or during lysis Composed of small proteins Composed of lipopolysaccharide Can be converted into a toxoid Click A for Exotoxin and B for Endotoxin

42 Epidemiology: The Study of Disease in Populations - Considers all forms of disease: heart disease, cancer, mental illness... Florence Nightingale: - Laid foundations of modern epidemiology - Before the discovery of the germ theory, she understood that filth contributed to disease. - Instituted revolutionary methods in military field hospitals, including separate linens and towels for each patient, cleaning of floors, and unclogging of sewage pipes - Kept meticulous notes and demonstrated that more men died of disease than traumatic injuries Florence Nightingale - Mini Biography

43 Tracking Disease in the Population Reportable or notifiable diseases: - Certain diseases must be reported to authorities. - Other diseases are reported on a voluntary basis. Network of agencies at local, district, state, national, and international levels keeps track of IDs Nationally notifiable diseases: Physicians are required to report occurrence. (also Table 11.10)??

44 Epidemiological Statistics Morbidity: Incidence of a specific notifiable disease. Mortality: Deaths from notifiable diseases. Morbidity rate: Number of people affected in relation to total population in a given time period. Mortality rate: Number of deaths from a disease in relation to total population in a given time period. Overall death rate from infectious diseases has dropped, although the the morbidity rate has remained high

45 Frequency of Cases Prevalence: How much of a disease is in population = Total # of cases in population Total # of persons in population X 100 = % Incidence: Rate of occurrence of new cases = # of new cases in a designated time period Total # of susceptible persons (Usually reported per 100,000 persons)

46 Fig. 11.9

47 Epidemiological Statistics cont. Common-source epidemic: Common exposure to a single source of infection over period of time Point-source epidemic: Subclassification of commonsource epidemic. Group is exposed over a relatively brief period. Everyone who becomes ill does so within one incubation period. Propagated epidemic: Infectious agent is communicable from person to person and is sustained over time in a population

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49 Epidemiological Statistics cont. Index case: first patient found in an epidemiological investigation. May not be the first case of the disease, but it is the first case that brought the epidemic to the attention of officials. first case of the disease = Sporadic: Occasional occurrence Endemic: Constantly present at Epidemic: Widespread occurrence at given time and in given area Pandemic:

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51 Case File: A Permanent Fix Universal Precautions Inside the Clinic: Fecal Transplants