1. Chapter 14 Principles of Disease and Epidemiology
Lectures prepared by Christine L. Case
© 2013 Pearson Education, Inc.

3. Introduction Pathogens- disease causing organisms
Our defenses either resist the pathogens or they can get into our body and cause temporary or permanent damage

4. 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

5. Normal Microbiota and the Host
Humans are generally free of microbes while in the uterus
At birth, microorganisms begin to establish themselves on our bodies.
Normal microbiota- permanently colonize the host
Transient microbiota- may be present for days, weeks, or months
Symbiosis- is the relationship between normal microbiota and the host

6. Many factors determine Normal Microbiota distrubution:
Nutrients
Physical and chemical factors- pH, temp
Host defenses
Mechanical factors- chewing, urine flow
Host conditions- age, diet, emotional state

7. Figure 14.1 Representative normal microbiota for different regions of the body.
Bacteria (orange
spheres) on the surface of the nasal epithelium
Bacteria (brown) on the lining of the stomach
Bacteria (orange) in the small intestine

8. Symbiosis- the relationship is needed by at least one of the organism
Commensalism- one organism benefits, and the other is unaffected
Mutualism- both organisms benefit
Parasitism- one organism benefits at the expense of the other
Opportunistic pathogens- usually don’t cause disease in a healthy person when they are in their normal habitat but do when they get moved
AIDS pt. becoming infected with Pneumocystis jirovecii

9. 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

10. Normal Microbiota by Body Region
Skin- Propionibacterium, Staphylococcus sp., Candida
Nose and Throat- Staphylococcus aureus and epidermidis, Streptococcus sp., Neisseria
Mouth- Candida sp.
Large Intestine- Escherichia coli, Proteus sp., Klebsiella sp., Clostridium difficile
Urinary and Reproductive Tracts- Pseudomonas sp., Klebsiella sp., Proteus sp., Candida albicans

11. Table 14.1 Normal Microbiota on the Human Body
Eyes (conjunctiva)
Nose and throat
(upper respiratory
system)
Mouth
Skin
Large intestine
Urinary and
reproductive
systems (lower
urethra in both
sexes and vagina
in females)

12. Koch’s Postulates
The same pathogen must be present in every case of the disease.
The pathogen must be isolated from the diseased host and grown in pure culture.
The pathogen from the pure culture must cause the disease when it is inoculated into a healthy, susceptible laboratory animal.
The pathogen must be isolated from the inoculated animal and must be shown to be the original organism.

13. Figure 14.3 Koch’s Postulates: Understanding Disease.
Microorganisms are isolated from a diseased or dead animal.
The microorganisms are
grown in pure culture. 3
The microorganisms are injected into a healthy laboratory animal. 1 2a
Colony
The microorganisms
are identified. 2b 4
Disease is reproduced in a laboratory animal. 5a
The microorganisms are isolated from this animal and grown in pure culture.
Microorganisms
are identified. 5b
The microorganism from the
diseased host caused the same
disease in a laboratory host.

14. Koch’s Postulates Organisms and their specific diseases:
Bacillus anthracis- anthrax
Mycobacterium tuberculosis- TB
Koch’s postulates are used to prove the cause of an infectious disease

15. Exceptions
Some microorganisms can only be grown in humans. This leads to ethical questions.
HIV
Some diseases all cause the same type of symptoms. Can be hard to distinguish.
Some organisms require specific environments to grow
Treponema pallidum can’t grow on an ARTIFICIAL media.
These organisms have to be grown using live specimens such as rats, guinea pigs, birds.

16. 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

17. Classifying Infectious Diseases
Communicable disease: a disease that is spread from one host to another
Genital herpes, Chicken Pox
Contagious disease: a disease that is easily spread from one host to another
Chicken Pox
Noncommunicable disease: a disease that is not transmitted from one host to another
Tetanus

18. Occurrence of a Disease
Incidence: fraction of a population that contracts a disease during a specific time; new cases
HIV cases in US ,300
Prevalence: fraction of a population having a specific disease at a given time; looks at old and new cases
HIV cases in the world in ,185,000
Sporadic disease: disease that occurs occasionally in a population

19. Occurrence of a Disease
Endemic disease: disease constantly present in a population
Colds
Epidemic disease: disease acquired by many hosts in a given area in a short time
Flu
Pandemic disease: worldwide epidemic
AIDS

20. Severity or Duration of a Disease
Acute disease: symptoms develop rapidly; usually short lived
Stomach virus, Flu
Chronic disease: disease develops slowly; usually long
TB, Hepatitis B, Mononucleosis
Subacute disease: symptoms between acute and chronic
Latent disease: disease with a period of no symptoms when the causative agent is inactive
Shingles

21. Vaccinations
Can provide short term or long term immunity against certain diseases.
Can stop diseases from spreading rapidly.
Herd immunity: immunity in most of a population

22. Extent of Host Involvement
Local infection: pathogens are limited to a small area of the body; where they enter
Abscesses
Systemic infection: an infection throughout the body spread by lymph or blood
Measles
Focal infection: systemic infection that began as a local infection
Strept throat  Scarlet Fever

23. 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 not multiplying
Septicemia: growth of bacteria in the blood
Toxemia: toxins in the blood
Viremia: viruses in the blood

24. Extent of Host Involvement
Primary infection: acute infection that causes the initial illness
Chicken pox- pustules
Secondary infection: opportunistic infection after a primary (predisposing) infection
Staphylococcus aureus- infection of pustules due to child scratching
Subclinical disease: no noticeable signs or symptoms (inapparent infection)
Poliovirus, Hepatitis A

25. 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

26. Development of Disease
Incubation period- period from initial infection until signs/symptoms are present; varies
Prodromal period- Mild symptoms
Period of Illness- Most severe signs/symptoms
Period of Decline- Signs/symptoms start to go away and get better
Period of Convalescence- Recovery

27. Incubation period (no signs or symptoms)
Figure 14.5 The stages of a disease.
Period of
illness
Period of
decline
Incubation period (no signs or symptoms)
Prodromal period (mild signs or symptoms)
Number of microbes
Period of convalescence
Most severe signs
and symptoms
Signs and
symptoms
Time

28. Reservoirs of Infection
Continual sources of infection
Humans: AIDS, gonorrhea
Carriers may have inapparent infections or latent diseases
Animals: rabies, Lyme disease
Some zoonoses may be transmitted to humans
Nonliving: botulism, tetanus
Soil
Water

29. Transmission of Disease
Contact
Direct: requires close association between infected and susceptible host
Indirect: spread by fomites
Droplet: transmission via airborne droplets
Small droplets travel farther (Airborne)
Large droplets travel not as far (Droplet)

30. Vehicle Transmission
Transmission by an inanimate reservoir (food, water, air)
Salmonella, Cholera, and Fungal infections

31. Vectors Arthropods, especially fleas, ticks, and mosquitoes
Transmit disease by two general methods:
Mechanical transmission: arthropod carries pathogen on feet
Houseflies, roaches
Biological transmission: pathogen reproduces in vector
Trypansoma sp.

32. Figure 14.8 Mechanical transmission.
Vectors

33. Nosocomial Infections
Are acquired as a result of a hospital stay or other healthcare settings
Affect 5–15% of all hospital patients
Increased in the last 20 years
United States Statistics:
2 million/year
20,000 deaths/year
8th cause of death

34. Figure 14.6b Contact transmission.
Preventing direct contact transmission through the use of gloves, masks, and face shields

35. Microorganisms in hospital environment
Figure 14.9 Nosocomial infections.
Microorganisms in hospital environment
Compromised host
Nosocomial infection
Chain of transmission

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

37. Compromised Host Resistance to infection is impaired due to
Disease- suppresses immune system
Surgery- incisions, anesthesia
Invasive procedures- putting things in the body that don’t belong there
Burns- missing skin
Drugs- can suppress immune system

38. Chain of Transmission Equipment being reused.
Contract from healthcare worker (passive carrier)
Patients grouped together in one area for specific treatments
Invasive procedures

40. Control of Nosocomial Infections
Aseptic techniques
Proper handling of contaminated materials
Handwashing
Staff education
Isolation
Prescribing antibiotics only when necessary
Infection control committees

41. Emerging Infectious Diseases
Diseases that are new, increasing in incidence, or showing a potential to increase in the near future

42. 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
Malaria

43. Emerging Infectious Diseases
Modern transportation
West Nile virus
Ecological disaster, war, and expanding human settlement
Animal control measures
Lyme disease
Public health failure
Diphtheria

44. 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)
Paper/report will come from this publication. Information for the paper is on Blackboard under Course Content in the MMWR PAPER folder.

45. Epidemiology Descriptive: collection and analysis of data
Snow
Analytical: comparison of a diseased group and a healthy group
Nightingale
Experimental: controlled experiments
Semmelweis

46. Epidemiology
Case reporting: health care workers report specified disease to local, state, and national offices
Nationally notifiable diseases: physicians are required to report occurrence

47. 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

48. Number of reported cases
Figure a & b Epidemiological graphs.
40,000
35,000
30,000
25,000
Number of reported cases
20,000
15,000
10,000
5,000
(a) Lyme disease cases, 1999–2010
600
500
400
300
Reported cases per
100,000 people
200
100
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month
(b) Lyme disease by month, 2009

49. Reported tuberculosis cases, 1948–2010
Figure 14.10c Epidemiological graphs.
120
100 80 60 40 20
Reported cases per
100,000 people
Year
Reported tuberculosis cases, 1948–2010