1. Principles of Disease and Epidemiology14
Principles of Disease and Epidemiology

2. Principles of Disease and Epidemiology
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

3. Infection and Disease The Adventures of Sherlock Holmes,
ETIOLOGY –cause of disease
PATHOGENISIS-how the disease develops
The Adventures of
Sherlock Holmes,
20th Century Fox-1939
Basil Rathbone
Nigel Bruce

4. Infection and Disease Infection and disease represents a balance.
A pathogen causes harm
A commensal can be part of the normal flora
The site in the body can determine the classification –E. coli in urine=bad; E. coli in colon = normal

5. NORMAL MICROBIOTA

6. Normal Microbiota and the Host
Locations of normal microbiota on and in the human body.
Table 14.1c

7. NORMAL MICROBIOTA You can contain 1013 cells
You also contain 1014 cells that are bacterial
These make up normal and transient flora

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.
Figure 14.1c

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 are live microbes applied to or ingested into the body, intended to exert a beneficial effect.

10. MICROBIAL COOPERATION MICROBES
PERIODONTAL DISEASE

11. OPPORTUNISTIC MICROBES
A good organism which gains entrance into a new site can be pathogenic

12. Koch’s Postulates
Koch's postulates are used to prove the cause of an infectious disease.
Figure 14.3 (2 of 2)

13. Koch’s Postulates
Koch's postulates are used to prove the cause of an infectious disease.
Figure 14.3 (1 of 2)

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

15. SYMBIOSES

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.
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.

18. Occurrence of 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.
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.

19. Figure 14.4

20. 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 patient is inactive.

21. 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.
Bacteremia: Bacteria in the blood.
Septicemia: Growth of bacteria in the blood.

22. 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).

23. 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

24. The Stages of a Disease
Figure 14.5

25. Reservoirs of Infection
Reservoirs of infection are 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

26. Transmission of Disease
Contact
Direct: Requires close association between infected and susceptible host.
Indirect: Spread by fomites.
Droplet : Transmission via airborne droplets.

27. Transmission of Disease
Figure 14.6a, d

28. Transmission of Disease
Vehicle: Transmission by an inanimate reservoir (food, water).
Vectors: Arthropods, especially fleas, ticks, and mosquitoes.
Mechanical: Arthropod carries pathogen on feet .
Biological: Pathogen reproduces in vector.

29. Transmission of Disease
Figures 14.7b, 14.8

30. Nosocomial (Hospital-Acquired) Infections
Are acquired as a result of a hospital stay.
5-15% of all hospital patients acquire nosocomial infections.
Figures 14.6b, 14.9

31. Relative Frequency of Nosocomial Infections
Table 14.5

32. Common Causes of Nosocomial Infections
Percentage of Nosocomial Infections
Percentage Resistant to Antibiotics
Gram + cocci
51%
29%-89%
Gram – rods
30%
3-32%
Clostridium difficile
13%
Fungi 6%

33. NOSOCOMIAL INFECTIONS
In the United States, it has been estimated that as many as one hospital patient in ten acquires a nosocomial infection, or 2 million patients a year. Estimates of the annual cost range from $4.5 billion to $11 billion and up. Nosocomial infections contributed to 88,000 deaths in the U.S. in One third of nosocomial infections are considered preventable.

34. NOSOCOMIAL INFECTIONS

35. Emerging Infectious Diseases
Diseases that are new, increasing in incidence, or showing a potential to increase in the near future.
Contributing factors
Genetic recombination
E. coli 0157, Avian influenza (H5N1)
Evolution of new strains
V. cholerae 0139
Inapproriate use of antibiotics and pesticides
Antibiotic resistant strains

36. Emerging Infectious Diseases
Changes in weather patterns
Hantavirus
Modern Transportation
West Nile virus
Ecological disaster, war, and expanding human settlement
Coccidioidomycosis
Animal control measures
Lyme disease
Public Health failure
Diphtheria

37. Crossing the Species Barrier
UN 13.3

38. Epidemiology
The study of where and when diseases occur
Figure 14.10

39. Epidemiology John Snow 1848-1849
Mapped the occurrence of cholera in London
Ignaz Semmelweis
Showed that hand washing decreased the incidence of puerperal fever
Florence Nightingale
1858
Showed that improved sanitation decreased the incidence of epidemic typhus

40. Descriptive
Collection and analysis of data regarding occurrence of disease
Snow
Analytical
Comparison of a diseased group and a healthy group
Nightingale
Experimental
Study of a disease using controlled experiments
Semmelweis
Case reporting
Health care workers report specified disease to local, state, and national offices
Nationally notifiable diseases
Physicians are required to report occurrence
PLAY
Animation: Epidemiology

41. “AIDS” to “Gonorrhea”; “Pertussis” to “Streptococcal Toxic Shock Syndrome”
Table 14.7 (1 of 2)

42. “Haemophilus influenzae” to “Mumps”; “Streptococcus pneumonaie” to “Yellow Fever”
Table 14.7 (2 of 2)

43. Centers for Disease Control and Prevention (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.

44. Centers for Disease Control and Prevention (CDC)
Collects and analyzes epidemiological information in the United States.
Publishes Morbidity and Mortality Weekly Report (MMWR)

45. TERMINOLOGY REVIEW Sign Symptom Syndrome Communicable Contagious
Non-communicable

46. TERMINOLOGY REVIEW Local Systemic Focal Sepsis
Septicemia – bacteremia, viremia, toxemia
Primary, Secondary, Subclinical

47. TERMINOLOGY REVIEW Incidence Prevalence Sporadic Endemic Epidemic
Pandemic

48. TERMINOLOGY REVIEW
What was the incidence of Aids in 2005?

49. TERMINOLOGY REVIEW
Acute
Subacute
Chronic
Latent
Herd Immunity

50. Now We Have Disease! Predisposing factors Resistance Incubation Period
Prodromal Period
Period of Disease
Period of Decline
Convalescence

51. Nonliving reservoirs (food & water)
SOURCES OF DISEASE
Human reservoirs
Animal reservoirs
Zoonotic Diseases
Nonliving reservoirs (food & water)

52. MOVE IT ON!
DIRECT CONTACT
INDIRECT CONTACT
DROPLET
VEHICLE

53. MECHANICAL VS. BIOLOGICAL
MOVE IT ON!
VECTORS
MECHANICAL VS. BIOLOGICAL

54. vectors
Ticks
Mosquitoes
Blackflies
Horseflies
Tsetse flies