Principles of Disease and Epidemiology

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

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M I C R O B I O L O G Ya n i n t r o d u c t i o n

ninth edition TORTORA FUNKE CASE

14Principles of Disease and

Epidemiology


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


Infection and Disease

ETIOLOGY –cause of

disease

PATHOGENISIS-how the

disease develops

The Adventures ofSherlock Holmes,20th Century Fox-1939Basil RathboneNigel Bruce


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


NORMAL MICROBIOTA


Normal Microbiota and the Host

Locations of normal

microbiota on and in

the human body.

Table 14.1c


NORMAL MICROBIOTA

You can contain 1013 cells

You also contain 1014 cells that are bacterial

These make up normal and transient flora



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



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.


MICROBIAL COOPERATION MICROBES

PERIODONTAL DISEASE


OPPORTUNISTIC MICROBES

A good organism which gains

entrance into a new site can be

pathogenic


Koch’s Postulates

Koch's postulates are

used to prove the

cause of an infectious

disease.

Figure 14.3 (2 of 2)


Koch’s Postulates

Koch's postulates are

used to prove the

cause of an infectious

disease.

Figure 14.3 (1 of 2)


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.


SYMBIOSES


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.


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.


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.

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 14.4


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.


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.


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).


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


The Stages of a Disease

Figure 14.5


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


Transmission of Disease

Contact

Direct: Requires close association between infected

and susceptible host.

Indirect: Spread by fomites.

Droplet : Transmission via airborne droplets.



Figure 14.6a, d



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.



Figures 14.7b, 14.8


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


Relative Frequency of Nosocomial Infections

Table 14.5


Percentage of Nosocomial Infections

Percentage Resistant to Antibiotics

Gram + cocci 51% 29%-89%

Gram – rods 30% 3-32%

Clostridium difficile 13%

Fungi 6%

Common Causes of Nosocomial Infections


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 1995.

One third of nosocomial

infections are considered

preventable.


NOSOCOMIAL INFECTIONS


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


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


Crossing the Species Barrier

UN 13.3


Epidemiology

The study of where

and when diseases

occur

Figure 14.10


John Snow 1848-1849 Mapped the occurrence of cholera in London

Ignaz Semmelweis 1846-1848 Showed that hand washing decreased the incidence of puerperal fever

Florence Nightingale 1858 Showed that improved sanitation decreased the incidence of epidemic typhus

Epidemiology


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

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Table 14.7 (1 of 2)

“AIDS” to “Gonorrhea”; “Pertussis” to “Streptococcal Toxic Shock Syndrome”

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Table 14.7 (2 of 2)

“Haemophilus influenzae” to “Mumps”; “Streptococcus pneumonaie” to “Yellow Fever”


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.


Collects and analyzes epidemiological information in

the United States.

Publishes Morbidity and Mortality Weekly Report

(MMWR) www.cdc.gov

Centers for Disease Control and Prevention (CDC)


TERMINOLOGY REVIEW

Sign

Symptom

Syndrome

Communicable

Contagious

Non-communicable


TERMINOLOGY REVIEW

Local

Systemic

Focal

Sepsis

Septicemia – bacteremia, viremia, toxemia

Primary, Secondary, Subclinical


TERMINOLOGY REVIEW

Incidence

Prevalence

Sporadic

Endemic

Epidemic

Pandemic


TERMINOLOGY REVIEW

What was the incidence of Aids in 2005?


TERMINOLOGY REVIEW

Acute

Subacute

Chronic

Latent

Herd Immunity


Now We Have Disease!

Predisposing factors

Resistance

Incubation Period

Prodromal Period

Period of Disease

Period of Decline

Convalescence


SOURCES OF DISEASE

Human reservoirs

Animal reservoirs

Zoonotic Diseases

Nonliving reservoirs (food &

water)


MOVE IT ON!

DIRECT CONTACT

INDIRECT CONTACT

DROPLET

VEHICLE


MOVE IT ON!


vectors

Ticks

Mosquitoes

Blackflies

Horseflies

Tsetse flies

Documents

Principles of Disease and Epidemiology