1. Disease, Disease Transmission, and Epidemiology
Chapter 14

2. Symbiotic Relationships Between Microbes and Their Hosts
Types of symbiosis
Mutualism
Commensalism
Parasitism 2

3. Table 14.1 The Three Types of Symbiotic Relationships

4. Figure 14.1 Mutualism as shown by wood-eating termites

5. Symbiotic Relationships Between Microbes and Their Hosts
Normal Microbiota in Hosts
Organisms that colonize the body’s surfaces without normally causing disease
Two types
__________microbiota 5

6. Symbiotic Relationships Between Microbes and Their Hosts
Normal Microbiota in Hosts
Acquisition of normal microbiota
Development in uterus is free of microorganisms
Microbiota begin to develop during birthing process
Much of your resident microbiota is established during first month of life 6

7. Symbiotic Relationships Between Microbes and Their Hosts
How Normal Microbiota Become Opportunistic Pathogens
Opportunistic pathogens
Normal microbiota that cause disease under certain circumstances
Conditions that provide opportunities for pathogens 7

8. What is a disease? Infection Disease
Most infections are eliminated by the bodies defenses
Disease
Infections may lead to disease

9. Causation of Disease Germ theory of disease
Disease caused by infections of pathogenic microorganisms
Robert Koch developed a set of postulates to prove a particular pathogen causes a particular disease
Exceptions to Koch’s postulates
HIV/AIDS
Not ethical
Syphilis
Not culturable in lab 9

10. The Nature of Infectious Disease
Manifestations of Disease: Symptoms and Signs
Symptoms
Signs
Asymptomatic
Infections that lack symptoms but may still have signs of infection and can be transmitted 10

11. Classification of Infectious Diseases
Terms used to classify infectious disease
_________disease (rapid onset, short period of time ex. Common cold)
_________disease (develop slowly, continual or recurrent ex. Hepatitis C, TB)
_________disease (pathogen remains inactive for a long period of time before becoming active ex. shingles) 11

12. The Stages of Infectious Disease
Many infectious diseases have five stages following infection
____________period (time between infection and first symptoms and signs of disease)
_____________period (short time, mild symptoms)
____________(severe stage, signs and symptoms most evident)
____________(gradual decline of signs and symptoms as body returns to normal due to immune response or drug treatment)
_____________(patient recovers no signs or symptoms)
Patient can be infectious at any stage of disease depending on the causative agent 12

13. Figure 14.10 The stages of infectious diseases
Incubation period (no signs or symptoms)
Prodromal period (vague, general symptoms)
Illness (most severe signs and symptoms)
Decline (declining signs and symptoms)
Convalescence (no signs or symptoms)
Number of microorganisms or intensity of signs or symptoms
Time

14. How do we acquire a disease causing organism?
Most pathogens cannot survive for long outside their host
A successful pathogen needs to overcome the innate and adaptive defenses long enough for the pathogen to multiply and exit the host
It is a disadvantage for the pathogen to actually kill a host, since the opportunity to be transmitted may be limited and it loses the source of nutrients 14

15. Reservoirs of infection
Reservoir may or may not be harmed by pathogen
Three types of reservoirs
__________reservoirs

16. Human reservoirs The principle living reservoir- the human body
Infected individuals who are ___________ but infective to others (before or after onset of illness)
Some individuals remain asymptomatic and infective for years (ex. Tuberculosis, syphilis, and AIDS) 16

17. Animal Reservoirs __________or Zoonotic diseases (150 diseases)
Diseases naturally spread from animal host to humans
Acquire zoonoses through various routes
_____________with animal or its waste (E. coli O157:H7)
__________animals (tape worm)
____________(Rabies)
____________(Lyme Disease) 17

18. Nonliving Reservoirs
_______________________can be reservoirs of infection
Presence of microorganisms often due to contamination by feces or urine
Can be naturally occurring in environment (Tetanus and botulism)
Water (Example: parasitic eggs or E. coli)
Meats and vegetables 18

19. The Movement of Pathogens Out of a reservoir: ______________
Pathogens leave host through portals of exit
Many portals of exit are the same as portals of entry
Pathogens often leave hosts in materials the body secretes or excretes 19

20. Seminal vesicles (semen and lubricating secretions)
Figure Portals of exit
Ear (earwax)
Broken skin (blood)
Skin (flakes)
Anus (feces)
Urethra (urine)
Seminal vesicles (semen and lubricating secretions)
Eyes (tears)
Nose (secretions)
Mouth (saliva, sputum)
In females: Mammary glands (milk, secretions)
Vagina (secretions, blood)

21. Movement of a pathogen into a host
Portals of Entry
Sites through which pathogens enter the body
Four major pathways
Broken skin
Insect bite
Anus
Ear
Conjunctiva of eye
Mouth
Placenta
Vagina
Penis
Urethra 21

22. Portals of Entry
Skin
Outer layer of dead skin cells acts as a barrier to pathogens
Some pathogens can enter through openings or cuts
Others burrow into or digest outer layers of skin 22

23. Portals of Entry Mucous membranes
Line the body cavities that are open to the environment
Respiratory tract is the most common site of entry
Entry is through the nose, mouth, or eyes
Gastrointestinal tract may be route of entry
Must survive the acidic pH of the stomach 23

24. Portals of Entry Placenta
Typically forms effective barrier to pathogens
Pathogens may cross the placenta and infect the fetus
Can cause spontaneous abortion, birth defects, premature birth
Listeria (lunch meats) 24

25. Portals of Entry Parenteral route Not a true portal of entry
A way portals of entry can be bypassed
Mechanically depositing pathogens directly into tissues beneath the skin or mucous membranes
Hypodermic needles
Thorns, nails, etc.. 25

26. Modes of Infectious Disease Transmission
Transmission is from a reservoir or a portal of exit to another host’s portal of entry
Three groups of transmission 26

27. Contact Transmission Direct Contact
One person physically touches another
Handshake
Sexual intercourse
Fecal-oral

28. Contact Transmission Indirect Contact
Transfer of pathogens via inanimate objects (called fomites)
Clothing
Doorknobs
Glasses and eating utensils
Ex. Scabies: Bedding serves as fomite involved in transmission

29. Contact Transmission: Droplet
Transmission of a pathogen through inhalation of respiratory droplets.
Large microbe saturated droplets fall to the ground no farther than 3 feet from release.
Close proximity necessary
Coughing
Sneezing
Examples of diseases:
Cold, Flu

30. Vehicle Transmission: Airborne
Transmission of a pathogen that is suspended in the air and travels through the air to another host
Very difficult to control!
Remains suspended indefinitely
Coughing
Sneezing
Examples of diseases:
Tuberculosis, Measles

31. Vehicle Transmission: Food
Usually digestive tract diseases
Contamination can occur in a variety of different ways
Animals can harbor pathogens
Salmonella
E. coli O157:H7
Inadvertently added during food preparation
No handwashing
Staphylococcus aureus
Cross-contamination
Cutting board used on meat and vegetables for your salad
Meat and vegetable processing facilities

32. Vehicle Transmission: Food
Toxin causes illness not the living organisms
Staphylococcus aureus and Clostridium botulinum

33. Vehicle Transmission: Food
Undercooked hamburger or chicken
Symptoms do not usually appear for at least 1 day
Diarrhea
Thorough cooking before consumption will kill the organisms
E. coli O157:H7
Salmonella

34. Vehicle Transmission: Water
Can involve large numbers of people
1993 Cryptosporidium parvum (intestinal parasite)
Watery diarrhea 10-15L a day
Infectious dose: less than 10 organisms
Milwaukee, WI
Infected ~400,000 people from municipal water source

36. Vector Transmission

37. 1. Biological Vector An organism transmits and serves as host.
Ex: Malaria: Part of life cycle of protozoan, Plasmodium, occurs inside the Anopheles mosquito

38. 2. Mechanical Vector
Ex: Trachoma (Blindness): Chlamydia trachomatis carried on feet of fly from infected person's eye to eye of new host

39. Epidemiology
Epidemiology focuses on the effect of a pathogen in a population
The study of where and when diseases occur and how they are transmitted in a population.
Why is this field important?
Earth’s population is becoming over populated.
Humans are relying more on mass food production and distribution
Travel to other countries very readily.
Leads to higher incidence, number of new cases of a disease in a population)
Prevalence, the total number of cases, new and already existing in a population

40. Occurrence of an infectious disease can be classified in terms of geographic distribution and frequency.
Sporadic
Endemic
Outbreak
Epidemic
Pandemic

41. Sporadic
Example:
Plague in U.S.

42. Endemic Endemic disease can lead to epidemic Example:
Pertussis in U.S.
Common cold
Influenza
Year
Reported Cases*
2000
7,867
2001
7,580
2002
9,771
2003
11,647
2004
25,827
2005
25,616
2006
15,632
2007
10,454
2008
13,278
2009
16,858
2010
27,550
2011*
18,719
*Total reported cases include those with unknown age.

43. Outbreak
Implies a cluster of cases occurring during a brief period of time and attacking a specific population, usually food borne
E. coli O157:H7 from contaminated food sources
Seventy-seven people sick and one died in a salmonella outbreak caused by contaminated ground turkey:
Centers for Disease Control 2011

44. Epidemic
Affecting an unusually large number of individuals within given region or population
Epidemic may lead to pandemic
H1N1 was epidemic in US in 2009
Pandemic- epidemic on more
than one continent
Example 2009 H1N1, also known as Swine Flu, breaks out and quickly spreads to more than 70 countries.

45. A disease affecting an increased proportion of the population over a wide geographic area, most often worldwide
Example:
AIDS
Pandemic

46. Local and state level health departments rely on doctors and hospitals to report infectious diseases.
In some cases the disease occurrence is nationally recorded to the Center for Disease Control (CDC).
Weekly updates can be viewed of the notable diseases in the Morbidity and Mortality Weekly Report (MMWR).

47. Epidemiology of Infectious Diseases
Hospital Epidemiology: Nosocomial Infections
Control of nosocomial infections
Disinfection, good housekeeping, bathing, sterile procedures, and HAND WASHING!
CDC reports that on average, health care workers wash their hands before interacting with patients only __________________ 47

48. Factors that influence nosocomial infections:>>>>>
Figure The interplay of factors that result in nosocomial infections
Factors that influence nosocomial infections:>>>>>
Infection can result from any one of these factors but usually it is a product of all three
Presence of microorganisms in hospital environment
Immunocompromised patients
Nosocomial infection
Transmission of pathogens between staff and patients and among patients

49. Emerging Disease What is an emerging Disease? Examples:
West Nile virus
HIV/AIDS
Cat Scratch Fever

50. Factors that contribute to disease emergence
Microbial evolution
Advances in technology
Mass production, widespread distribution and importation of food
Climate Change

51. Reemerging Diseases Resurgence of old diseases due to:
Diseases include:
TB, Pertussis

52. Tuberculosis reemerging in US
Mycobacterium tuberculosis
Causes an infection of the lower respiratory system
Inhalation of airborne bacteria from infected persons
9 million people each year develop TB
2 million deaths
About 2 billion people world wide are infected
14,000 cases annually in US usually from foreign born individuals. Increasing at rate of about 2% each year.

53. Pertussis commonly called whooping cough
Bordetella pertussis
Causes an infection of the lower respiratory system
Before DTP vaccination 50% of individuals would develop pertussis.
Vaccination significantly decreased this disease
Since 1980s number of cases has increased significantly affecting adults and adolescents.
Individuals are not up to date on booster shots which are intended to boost immunity
Immunity to the DTP vaccine declines after a few years
No protection by age 12