1. Chapter 14
Principles of Disease and Epidemiology

2. Pathology, Infection, and Disease
Disease is an abnormal state in which part or all of the body is not properly adjusted or is incapable of performing normal functions.
Pathology is the scientific study of disease.
Etiology (cause)
Pathogenesis (development)
Structural and functional changes brought about by disease with their final effects on the body
Infection is the invasion and growth of pathogenic microorganisms in the body.

3. Pathology, Infection, and Disease
Infection disease
Presence of particular microorganism in part of the body where is not usually found.
When a microorganism overcomes the body’s defenses, a state of disease results.
Pathogens - disease-causing microorganisms.
Pathogenic microorganisms have special properties that allow them to invade the human body or produce toxins.
A host is an organism that shelters and supports the growth of pathogens.

4. Normal Microbiota 
Animals, including humans, are usually germfree in utero (used in biology to describe the state of an embryo or fetus )
Microorganisms begin colonization in and on the surface of the body soon after birth
Normal microbiota - microorganisms that establish permanent colonies inside or on the body without producing disease.
Staphylococcus on epidermis and mucus membranes;
Escherichia coli in colon
Transient microbiota are microbes that are present for various periods and then disappear.
Although these types of organisms may colonize a host and reproduce briefly, the defenses of the human body do not allow them to become permanent.

5. Relationships Between the Normal microbiota and the Host
Symbiosis - living together - long-term interaction between two or more different biological species
The three types of symbiosis
Normal microbiota and the host exist in symbiosis
Opportunistic pathogens
Opportunistic pathogens do not cause disease under normal conditions (live in their normal habitat) but cause disease under special conditions.
Streptococcus pneumoniae
E.coli
E.coli (in colon)
Synthesize vitamin K
Mycobacteria
(in the ear)
Disease-causing
bacteria

6. Normal Microbiota and the Host
Locations of normal microbiota on and in the human body
100 trillion non-pathogenic bacteria/microorganisms that reside in or on a human body
Human body is built by 10 trillion cells
Human body/Commensal microbiota exist as a community
Figure 14.2

7. Normal Microbiota or Microbiome
Microbiome - collective genomes of all the microorganisms (bacteria, fungi and viruses) that reside in a person, literally share our body space

8. Microbiome and human body environment
Microbial community vary at different body sites on the same person (different ecosystem)
Bacteria of a specific body site from different persons have more common characteristic (common ecosystem).
The microbiome of a healthy and diseased person looks very different (rearranged ecosystem)

9. Microbiome and metabolic activity
Gut microbiome – “forgotten organ”
Produce hydrolytic enzymes - help our digestive system – they can vary
Synthesize vitamins - B2, B12 and folic acid – slight variation
Skin and gut microbiome
Stabilize epithelial homeostasis and barrier function
Modulate our innate and adaptive immunity
Prevent growth of pathogens
Production of antimicrobial substances
Compete for the nutrients

10. What is a healthy Microbiome?
Who we are ?
Microbiome
(bacterial
Phenotype)
Individual genetic material
What we eat
(diet)
Homeostasis
Health
Low risk of allergies
Infection resistance
Perturbation
Diseases
Allergies
Metabolic syndrome
Obesity
Infections
What is a healthy Microbiome?
One size does NOT fit all - Each person’s microbiome is unique

11. Relationships Between the Normal Microbiota and other microorganisms
Microbial antagonism.
Normal microbiota can prevent pathogens from causing an infection by competing for nutrition.
Produce substances harmful for invading organisms
E. coli produce bacteriocines
Affecting condition as pH or available oxygen
Cooperation Among Microorganisms 
In some situations, one microorganism makes it possible for another to cause a disease or produce more severe symptoms
Streptococci that colonize the teeth

12. How to take care of our “second genome”
We are what we eat
Probiotics – application of life microbial culture
Typically lactic acid producing bacteria ingested to aid digestion and protect intestine from pathogens
Prebiotics - refer to chemicals that induce the growth and/or activity of commensal microorganisms
Mix of bacteria instead of antibiotics
Fecal transplantation
Restoration of normal microbiota

13. The Etiology of Infectious Diseases
Koch’s postulates are criteria for establishing that specific microbes cause specific diseases.
Koch’s postulates have the following requirements:
1. The same pathogen must be present in every
case of the disease;
2. The pathogen must be isolated in pure culture;
3. The pathogen isolated from pure culture must
cause the same disease in a healthy, susceptible
laboratory animal;
4. The pathogen must be isolated from the
inoculated laboratory animal and must be shown
to be the original organism

14. Exceptions to Koch’s Postulates
Koch’s postulates are modified to establish etiologies of diseases caused by viruses and some bacteria, which cannot be grown on artificial media.
Some diseases have unequivocal signs and symptoms.
Tetanus - affects the nervous system and causes painful, uncontrolled muscle spasms
Some diseases may be caused by a variety of microbes.
Pneumonia and nephritis
Some pathogens, cause several different diseases.
Streptococcus pyogenes – sore throat, scarlet fiver, skin infections,
Certain pathogens, such as HIV, cause disease in humans only.

15. Classifying Infectious Diseases 1. Patient Appearance
Every disease alters body structures and functions
A patient may exhibit:
Symptoms (subjective changes in body functions)
Pain or body discomfort
Signs (measurable changes)
Fever, swelling, paralysis
A physician uses signs to make a diagnosis (identification of the disease)
Syndrome - a specific group of symptoms or signs that always accompanies a specific disease

16. Classifying Infectious Diseases 2. Spreadability
Communicable diseases are transmitted from one host to another.
Chicken pox, genital herpes, tuberculosis
A contagious disease is one that is easily spread from one person to another.
Chicken pox
Noncommunicable diseases are caused by microorganisms that normally grow outside the human body and are not transmitted from one host to another
Tetanus - Clostridium tetani

17. Classifying Infectious Diseases 3
Classifying Infectious Diseases 3. Occurrence of a Disease  (frequency of occurrence)
Sporadic – occur only occasionally in population
Typhoid fever
Endemic – constantly present in a population
Common cold
Epidemic – if many people in a given area acquire a certain disease in a relatively short period
Influenza
Pandemic – An epidemic disease that occurs worldwide
Some influenza, AIDS
Disease occurrence is reported by:
Incidence - Number of new disease cases per population at risk ( indicator of the spread of the disease)
Measured over a given time interval
Prevalence - Number of current ( old and new) cases per population at risk ( how seriously and how long the disease affects a population)
Fraction of a population having a specific disease at a given time
Herd immunity is the presence of immunity to a disease in most of the population.
Vaccination (immunization) prevent spread of the disease

18. Classifying Infectious Disease 4. Severity and Duration of a Disease
The scope of a disease can be defined as:
Acute – develops rapidly but last for short time
influenza, common cold
Chronic - develop slowly, continual or recurrent for long time
tuberculosis
Subacute – intermediate between acute and chronic
some brain diseases, endocarditis
Latent – the causative agent remains inactive for a time but than becomes active to produce symptoms of the disease .
shingles

19. Classifying Infectious Disease 5. Extent of Host Involvement
Local infection: Pathogens are limited to a small area of the body
abscesses
Systemic infection: An infection throughout the body by blood and/or lymph
Bacteremia: Bacteria in the blood
Sepsis: Toxic inflammatory condition arising from the spread of microbes, especially bacteria or their toxins, from a focus of infection
Septicemia: Growth of bacteria in the blood
Toxemia: Toxins in the blood
Viremia: Viruses in the blood
Focal infection: Systemic infection that began as a local infection
Local tooth infection can moves via blood or lymph to set up a new infection at another site - rheumatoid arthritis
Primary infection: Acute infection that causes the initial illness
Secondary infection: Opportunistic infection after the primary infection (predisposing) has weakened the body defense
Subclinical infection: No noticeable signs or symptoms (inapparent infection)

20. Predisposing Factors
A predisposing factor is one that makes the body more susceptible to disease or alters the course of a disease.
Gender (short urethra in females)
Climate and weather
Age
Fatigue
Inadequate nutrition.
Inherited traits, such as the sickle-cell anemia (SCA)
Chemotherapy

21. Patterns of Disease Development of Disease
1. The incubation period is the time interval between the initial infection and the first appearance of signs and symptoms.
2. The prodromal period is characterized by the appearance of the first mild signs and symptoms.
3. During the period of illness, the disease is at its height, and all disease signs and symptoms are apparent.
4. During the period of decline, the signs and symptoms subside.
5. During the period of convalescence, the body returns to its predeceased state, and health is restored.

22. The Spread of Infection
1. Reservoir of Infection - A continual source of infection
Human reservoirs of infection - People who have a disease or are carriers of pathogenic microorganisms.
Sick people = actively ill
Carriers = one who harbors disease organisms in their body without manifest symptoms (healthy)
Latent infection carriers = contagious during incubation period or convalescent period
Zoonoses - are diseases that affect wild and domestic animals and can be transmitted to humans.
Direct contact with animal or its waste
Eating animals
Bloodsucking arthropods
Nonliving reservoirs - Soil, water, and food can be reservoirs of infection
Presence of microorganisms is often due to contamination by feces or urine.

23. The Spread of Infection
2. Transmission of Disease 
Direct contact - involves close physical contact between the source of the disease and a susceptible host.
Indirect contact - transmission by fomites (inanimate objects)
Vehicle transmission -transmission by a medium such as water, food, or air.
Droplet transmission - transmission via saliva or mucus in coughing or sneezing
Airborne transmission refers to pathogens carried on water droplets or dust for a distance greater than 1 meter.
Arthropod vectors carry pathogens from one host to another
mechanical transmission passively carry pathogens on body parts e.g. houseflies
biological transmission from bites: usually involves complex life cycle of pathogen cycling between vector and host (e.g. mosquito - malaria)

24. Nosocomial (Hospital-Acquired) Infections
A nosocomial infection is any infection that is acquired during the course of stay in a hospital, nursing home, or other health care facility.
(2011) Healthcare-associated infections (HAI) are defined as infections not present and without evidence of incubation at the time of admission to a healthcare setting.
About 5 to 15% of all hospitalized patients acquire nosocomial infections (bloodstream infection, pneumonia, and urinary tract infection)

25. 1. Microorganisms in the Hospital environment
Certain normal microbiota are often responsible for nosocomial infections when they are introduced into the body through such medical procedures as surgery and catheterization.
Opportunistic, drug-resistant bacteria are the most frequent causes of nosocomial infections.

26. 2. Compromised Host 
Patients which are the most susceptible to nosocomial infections:
burns
surgical wounds
suppressed immune systems

27. Chain of Transmission of nosocomial infections
Direct contact
staff members and patients
between patients.
Indirect contact
Fomites such as catheters, syringes, and respiratory devices
Ventilation system - airborne transmission

28. Control of Nosocomial Infections
Aseptic techniques can prevent nosocomial infections.
Washing hands before inserting a catheter
Proper handling contaminated materials.
Hospital infection control staff members are responsible for overseeing the proper cleaning, storage, and handling of equipment and supplies.

29. 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 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
Modern transportation
Spread to new geographic areas
Ecological disaster, war, and expanding human settlement
Coccidioidomycosis
Animal control measures
Lyme disease
Public health failure
Diphtheria

30. Epidemiology The study of where and when diseases occur
when the disease occurs
to whom (age, race, class etc.)
mode of transmission
reservoirs
effective methods of control
plans to prevent future outbreaks
Descriptive epidemiology.
collection of data describing the occurrence of disease (affected people, place and period of disease)
Analytical epidemiology.
A group of infected people is compared with an uninfected group.
Experimental epidemiology
Controlled experiments designed to test hypotheses are performed.

31. Epidemiology Centers for Disease Control and Prevention (CDC)
Collects and analyzes epidemiological information in the United States
Publishes Morbidity and Mortality Weekly Report (MMWR)
Nationally notifiable diseases (contagious and/or deadly diseases)
Physicians are required to report occurrence of specified disease to local, state, and national offices.
Case reporting provides data on incidence and prevalence
Morbidity: Incidence of a specific notifiable disease.
Morbidity rate: Number of people affected in relation to the total population in a given time period
Mortality: Deaths from notifiable diseases
Mortality rate: Number of deaths from a disease in relation to the population in a given time

32. Epidemiology, Epidemiological graphs

33. Learning objectives
Define pathology, etiology, infection, and disease.
Define normal and transient microbiota, and microbiom.
Compare commensalism, mutualism, and parasitism, and give an example of each.
Contrast normal and transient with opportunistic microbes.
List Koch’s postulates.
Differentiate a communicable from a noncommunicable disease.
Categorize diseases according to frequency of occurrence.
Categorize diseases according to severity.
Define herd immunity.
Identify four predisposing factors for disease.
Put the following terms in proper sequence in terms of the pattern of disease: period of decline, period of convalescence, period of illness, prodromal period, incubation period.
Define reservoir of infection.
Contrast human, animal, and nonliving reservoirs, and give one example of each.
Explain three methods of disease transmission.
Define nosocomial infections and explain their importance.
Define compromised host.
List several methods of disease transmission in hospitals.
Explain how nosocomial infections can be prevented.
Define epidemiology and describe three types of epidemiologic investigation.
Identify the function of the CDC