Disease

1
Disease Epidemiology and Control

• Introduction to Microbiology
• Chapters 14 and 20

2
Epidemiology

• The study of where and when diseases occur
• Centers for Disease Control and Prevention (CDC)
• Collects and analyzes epidemiological information
  in the United States
• Publishes Morbidity and Mortality Weekly Report
  (MMWR)
• www.cdc.gov

3
Epidemiology
John Snow 18481849 Mapped the occurrence of cholera in London
Ignaz Semmelweis 18461848 Showed that handwashing decreased the incidence of puerperal fever
Florence Nightingale 1858 Showed that improved sanitation decreased the incidence of epidemic typhus
4
Epidemiology

• Descriptive Collection and analysis of data
• Snow
• Analytical Comparison of a diseased group and a
  healthy group
• Nightingale
• Experimental Controlled experiments
• Semmelweis

5
Epidemiology

• Case reporting Health care workers report
  specified disease to local, state, and national
  offices
• Nationally notifiable diseases Physicians are
  required to report occurrence

6
The CDC

• Morbidity Incidence of a specific notifiable
  disease
• Mortality Deaths from notifiable diseases
• Morbidity rate Number of people affected in
  relation to the total population in a given time
  period
• Mortality rate Number of deaths from a disease
  in relation to the population in a given time

7
Pathology, Infection, and Disease

• Pathology The study of disease
• Etiology The study of the cause of a disease
• Pathogenesis The development of disease
• Infection Colonization of the body by pathogens
• Disease An abnormal state in which the body is
  not functioning normally

8
Normal Microbiota and the Host

• Transient microbiota may be present for days,
  weeks, or months
• Normal microbiota permanently colonize the host
• Symbiosis is the relationship between normal
  microbiota and the host

9
Representative Normal Microbiota
Figure 14.1
10
Symbiosis

• In commensalism, one organism benefits, and the
  other is unaffected
• In mutualism, both organisms benefit
• In parasitism, one organism benefits at the
  expense of the other
• Some normal microbiota are opportunistic pathogens

11
Normal Microbiota and the Host

• Microbial antagonism is a competition between
  microbes.
• Normal microbiota protect the host by
• Occupying niches that pathogens might occupy
• Producing acids
• Producing bacteriocins
• Probiotics Live microbes applied to or ingested
  into the body, intended to exert a beneficial
  effect

12
Classifying Infectious Diseases

• Symptom A change in body function that is felt
  by a patient as a result of disease
• Sign A change in a body that can be measured or
  observed as a result of disease
• Syndrome A specific group of signs and symptoms
  that accompany a disease

13
Classifying Infectious Diseases

• Communicable disease A disease that is spread
  from one host to another
• Contagious disease A disease that is easily
  spread from one host to another
• Noncommunicable disease A disease that is not
  transmitted from one host to another

14
Occurrence of a Disease

• Incidence Fraction of a population that
  contracts a disease during a specific time
• Prevalence Fraction of a population having a
  specific disease at a given time
• Sporadic disease Disease that occurs
  occasionally in a population

15
Occurrence of a Disease

• Endemic disease Disease constantly present in a
  population
• Epidemic disease Disease acquired by many hosts
  in a given area in a short time
• Pandemic disease Worldwide epidemic
• Herd immunity Immunity in most of a population

16
Severity or Duration of a Disease

• Acute disease Symptoms develop rapidly
• Chronic disease Disease develops slowly
• Subacute disease Symptoms between acute and
  chronic
• Latent disease Disease with a period of no
  symptoms when the causative agent is inactive

17
Extent of Host Involvement

• Local infection Pathogens are limited to a small
  area of the body
• Systemic infection An infection throughout the
  body
• Focal infection Systemic infection that began as
  a local infection
• Superinfection occurs when a pathogen develops
  resistance to the drug being used for treatment
  or when normally resistant microbiota multiply
  excessively, adding to infection.

18
Extent of Host Involvement

• Sepsis Toxic inflammatory condition arising from
  the spread of microbes, especially bacteria or
  their toxins, from a focus of infection
• Bacteremia Bacteria in the blood
• Septicemia Growth of bacteria in the blood

19
Extent of Host Involvement

• Toxemia Toxins in the blood
• Viremia Viruses in the blood
• Primary infection Acute infection that causes
  the initial illness
• Secondary infection Opportunistic infection
  after a primary (predisposing) infection
• Subclinical disease No noticeable signs or
  symptoms (inapparent infection)

20
Predisposing Factors

• Make the body more susceptible to disease
• Short urethra in females
• Inherited traits, such as the sickle cell gene
• Climate and weather
• Fatigue
• Age
• Lifestyle
• Chemotherapy

21
The Stages of a Disease
Figure 14.5
22
The Spread of Infection

• Reservoirs of Infection
• Continual sources of infection
• Human AIDS, gonorrhea
• Carriers may have inapparent infections or
  latent diseases
• Animal Rabies, Lyme disease
• Some zoonoses may be transmitted to humans
• Nonliving Botulism, tetanus
• Soil

23
The Spread of Infection Transmission Types

• Contact
• Vehicle
• Vector

24
Transmission of Disease

• Contact
• Direct Requires close association between
  infected and susceptible host
• Indirect Spread by fomites
• Fomite inanimate object that can spread
  disease.
• Example toys, clothing, utensils, etc.
• Droplet Transmission via airborne droplets

25
Transmission of Disease

• Vehicle
• Contact with food, water, other liquids
• These are constantly taken into the body, so they
  serve as vehicles into the body.

26
Transmission of Disease

• Vector
• Transmission from an animal (insect)

27
Transmission of Disease
Figure 14.6a, d
28
Vehicle Transmission

• Transmission by an inanimate reservoir (food,
  water, air)

Figure 14.7b
29
Nosocomial Infections

• Are acquired as a result of a hospital stay
• Affect 515 of all hospital patients

Figure 14.6b
30
Nosocomial Infections
Figure 14.9
31
Nosocomial Infections
Table 14.5
32
Common Causes of Nosocomial Infections
Percentage of Total Infections Percentage Resistant to Antibiotics
Coagulase-negative staphylococci 25 89
S. aureus 16 80
Enterococcus 10 29
Gram-negative rods 23 5-32
C. difficile 13 None
33
MRSA

• USA100 92 of health care strains
• USA300 89 of community-acquired strains

Clinical Focus, p. 422
34
Which Procedure Increases the Likelihood of
Infection Most?
Clinical Focus, p. 422
35
Emerging Infectious Diseases

• Diseases that are new, increasing in incidence,
  or showing a potential to increase in the near
  future

36
Emerging Infectious Diseases

• Contributing factors
• Genetic recombination
• E. coli O157, avian influenza (H5N1)
• Evolution of new strains
• V. cholerae O139
• Inappropriate use of antibiotics and pesticides
• Antibiotic-resistant strains
• Changes in weather patterns
• Hantavirus

37
Emerging Infectious Diseases

• Modern transportation
• West Nile virus
• Ecological disaster, war, and expanding human
  settlement
• Coccidioidomycosis
• Animal control measures
• Lyme disease
• Public health failure
• Diphtheria

38
Crossing the Species Barrier
Clinical Focus, p. 371
39
Treatment Antibiotics/Antimicrobials

• Chemotherapy The use of drugs to treat a disease
• Antimicrobial drugs Interfere with the growth of
  microbes within a host
• Antibiotic A substance produced by a microbe
  that, in small amounts, inhibits another microbe
• Selective toxicity A drug that kills harmful
  microbes without damaging the host

40
Antimicrobial Drugs

• 1928 Fleming discovered penicillin, produced by
  Penicillium
• 1940 Howard Florey and Ernst Chain performed
  first clinical trials of penicillin

Figure 1.5
41
Most Antibiotics come from other Microorganisms
42
The Spectrum of Antimicrobial Activity
43
The Spectrum of Antimicrobial Activity

• Broad spectrum
• Treats a variety of microbes
• Narrow spectrum
• Treats few microbes

44
The Action of Antimicrobial Drugs

• Bactericidal
• Kill microbes directly
• Bacteriostatic
• Prevent microbes from growing
• Ideally, an antimicrobial should target the
  pathogen only and not disrupt normal microbiota
• Risk vs. Benefit Analysis

45
The Action of Antimicrobial Drugs
46
Commonly used Antimicrobials Modes of Action

• Inhibitors of Cell Wall Synthesis
• Antimycobacterial Antibiotics
• Inhibitors of Protein Synthesis
• Injury to the Plasma Membrane
• Inhibitors of Nucleic Acid (DNA/RNA) Synthesis
• Competitive Inhibitors of the Synthesis of
  Essential Metabolites

47
Commonly Used Antimicrobials

• Antibacterial Antibiotics Inhibitors of Cell
  Wall Synthesis
• All penicillins (natural and semisynthetic)
• Carbapenems
• Cephalosporins
• Bacitracin
• Vancomycin

48
Commonly Used Antimicrobials

• Antimycobacterial Antibiotics
• Isoniazid (INH) and ethambutol inhibit cell wall
  synthesis in mycobacteria.

49
Commonly Used Antimicrobials

• Inhibitors of Protein Synthesis
• Chloramphenicol, aminoglycosides, tetracyclines,
  macrolides, and streptogramins inhibit protein
  synthesis at 70S ribosomes.
• Oxazolidinones prevent formation of 70S
  ribosomes.

50
Commonly Used Antimicrobials

• Injury to the Plasma Membrane
• A new class of antibiotics inhibits fatty-acid
  synthesis, essential for plasma membranes.
• Polymyxin B and bacitracin cause damage to plasma
  membranes.

51
Commonly Used Antimicrobials

• Inhibitors of Nucleic Acid (DNA/RNA) Synthesis
• Rifamycin inhibits mRNA synthesis it is used to
  treat tuberculosis.
• Quinolones and fluoroquinolones inhibit DNA
  gyrase for treating urinary tract infections.

52
Commonly Used Antimicrobials

• Competitive Inhibitors of the Synthesis of
  Essential Metabolites
• Sulfonamides competitively inhibit folic acid
  synthesis.

53
Antiviral Drugs

• Protease inhibitors
• Indinavir HIV
• Integrase inhibitors
• HIV
• Inhibit attachment
• Zanamivir Influenza
• Block CCR5 HIV
• Inhibit uncoating
• Amantadine Influenza
• Nucleoside and Nucleotide Analogs
• Inhibit DNA/RNA synthesis
• Enzyme inhibitors
• Inhibit fusion, Inhibit attachment, Inhibit
  uncoating
• Interferons
• Prevent spread of viruses to new cells

54
Antiprotozoan Drugs

• Metronidazole
• Damages DNA
• Entamoeba, Trichomonas
• Nitazoxanide
• Interferes with metabolism of anaerobes

55
Antihelminthic Drugs

• Niclosamide
• Prevents ATP generation
• Tapeworms
• Praziquantel
• Alters membrane permeability
• Flatworms

Figure 12.26
56
Antihelminthic Drugs

• Mebendazole
• Inhibits nutrient absorption
• Intestinal roundworms
• Ivermectin
• Paralyzes worm
• Intestinal roundworms

Figure 12.28a
57
Testing Effectiveness of Treatment

• Disk Diffusion Test (Kirby Bauer)
• Broth Dilution Test
• MIC (minimal inhibitory concentration) Test
• The E-test
• Microtitre plates

58
The Disk-Diffusion Method
Figure 20.17
59
The E Test
Figure 20.18
60
Microtitre Plate
Figure 20.19
61
Antibiotic Resistance

• A variety of mutations can lead to antibiotic
  resistance
• Mechanisms of antibiotic resistance
• Enzymatic destruction of drug
• Prevention of penetration of drug
• Alteration of drug's target site
• Rapid ejection of the drug
• Resistance genes are often on plasmids or
  transposons that can be transferred between
  bacteria

62
Antibiotic Resistance

• Misuse of antibiotics selects for resistance
  mutants. Misuse includes
• Using outdated or weakened antibiotics
• Using antibiotics for the common cold and other
  inappropriate conditions
• Using antibiotics in animal feed
• Failing complete the prescribed regimen
• Using someone else's leftover prescription

63
Effects of Combinations of Drugs

• Synergism occurs when the effect of two drugs
  together is greater than the effect of either
  alone
• Antagonism occurs when the effect of two drugs
  together is less than the effect of either alone

64
Synergism between Two Different Antibiotics
Figure 20.23
65
Antagonism Between Antimicrobials The D-test
66
The Future of Antimicrobial Treatment and
Development

• Chemicals produced by plants and animals are
  providing new antimicrobial agents called
  antimicrobial peptides.
• Phage therapy is also something that is being
  investigated for new treatment