powerpoint lecture cslo8 explain transmission and

PowerPoint® Lecture

Presentations prepared by

Mindy Miller-Kittrell,

North Carolina

State University

C H A P T E R

© 2014 Pearson Education, Inc.

Infection,

Infectious

Diseases, and

Epidemiology

14

CSLO8. Explain transmission and virulence

mechanisms of cellular and acellular infectious agents.


Symbiotic Relationships Between Microbes and

Their Hosts

Symbiosis means "to live together“

• We have symbiotic relationships with countless

microorganisms

• 3 Types of symbiosis

• Mutualism

• Commensalism

• Parasitism

CONCEPT 14.1


Any parasite that cause disease

is called a pathogen

CONCEPT 14.1


Symbiotic Relationships Between Microbes and

Their Hosts

Normal Microbiota in Hosts

• Organisms that colonize the body's surfaces without

normally causing disease is called normal microbiota

• Also termed normal flora and indigenous microbiota

• Two types

1) Resident microbiota

2) Transient microbiota

CONCEPT 14.2



1) Resident microbiota

• Are a part of the normal microbiota throughout life

• Are mostly commensal (one benefits – other - no benefit no

harm)

CONCEPT 14.3



2) Transient microbiota

• Found in the same regions as resident microbiota but remain

for short time

• Cannot persist in the body because of following reasons

1) Competition from other microorganisms

2) Elimination by the body's defense cells

3) Chemical or physical changes in the body

CONCEPT 14.4


Acquisition of Normal Microbiota in Hosts

• While fetus is developing in womb which is free of

microorganisms called axenic)

• Microbiota begin to develop during birthing process

• Much of one's resident microbiota established during first

months of life

(free of microorganisms = axenic)

CONCEPT 14.5


What are Opportunistic Pathogens ?

Opportunistic pathogens are normal microbiota that cause disease

under certain circumstances

CONCEPT 14.6

There are 3 ways by which Normal Microbiota become

Opportunistic Pathogens

1) Introduction of normal microbiota into unusual site in body e.g. E.coli

2) Immune suppression e.g. AIDs

3) Changes in relative abundance of the normal microbiota may

decrease microbial antagonism/competition and allow opportunity for a

member to thrive and cause disease

CONCEPT 14.7


Reservoirs of Infectious Diseases of Humans

Reservoirs of infection are sites

where pathogens are maintained as a source of infection

Most pathogens cannot survive for long outside of

their host

Three types of reservoirs

1) Animal reservoir

2) Human carriers

3) Nonliving reservoir

CONCEPT 14.8

CONCEPT 14.9


1) Animal Reservoirs are called Zoonoses

Zoonoses are Diseases naturally spread from animal host to humans

Humans can acquire zoonoses through various routes

A) Direct contact with animal or its waste

B) Eating animals – fruit bats –Ebola connection

C) Bloodsucking arthropods

CONCEPT 14.10

CONCEPT 14.11


e.g. Rabies virus – (bats/foxes/skunks)

– spread to domesticated pets – then to

humans


Reservoirs of Infectious Diseases of Humans

2) Human Carriers

• Asymptomatic infected individuals can be infective to others

• Healthy carriers may have defensive systems that protect them

• Some individuals eventually develop illness while others never get sick

3) Nonliving Reservoirs

• Soil, water, and food can be reservoirs of infection

• Presence of microorganisms often due to contamination by feces or urine

CONCEPT 14.12

CONCEPT 14.13


Exposure to Microbes: Contamination/Infection/Disease

• Contamination = the mere presence of microbes in or on the

body

• Infection is the invasion of the host by a pathogen

• Infection = when organism evades body's external defenses,

multiplies, and becomes established in the body

• Infection – may or may not result in disease

• Disease results if the invading pathogen alters normal body

functions

• Disease is also referred to as morbidity

CONCEPT 14.14


The Invasion and Establishment of Microbes in

Hosts: Infection

Portals of Entry are sites through which pathogens

enter the body

4 major portals of entry

1. Skin

2. Mucous membranes

3. Placenta

4. Entry via the parenteral route circumvents the

usual portals - punctures by nail, needle

CONCEPT 14.15


The Invasion and Establishment of Microbes in Hosts: Infection

1) 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 enter by burrowing into or digesting outer layers of skin

CONCEPT 14.16



2) Portals of Entry : Mucous Membrane

• Line the body cavities that are open to the environment

• Provide a moist, warm environment hospitable to pathogens

• Respiratory tract is the most common site of entry

• Entry is through the nose, mouth, or eyes (viruses) –

cold/influenza virus

• Gastrointestinal tract may be route of entry

• Must survive the acidic pH of the stomach

CONCEPT 14.17



3) Portals of Entry : Placenta

• Typically placenta forms effective barrier to pathogens

• Pathogens may cross the placenta and infect the fetus

• Can cause spontaneous abortion, birth defects, premature birth

CONCEPT 14.18



4) Portals of Entry : Parenteral route

• Not a true portal of entry

• Means by which portals of entry can be circumvented

• Pathogens deposited directly into tissues beneath the skin or

mucous membranes – nail/thorn/needles/cuts/bites/surgery

CONCEPT 14.19



The Role of Adhesion in Infection

• Adhesion is process by which microorganisms attach themselves

to cells and is required to successfully establish colonies within the

host

• Uses adhesion factors

1) Specialized structures

1) Attachment proteins

CONCEPT 14.20

fimbriae/glycocalyx


Attachment proteins help in adhesion

• Found on viruses and many bacteria

• Viral or bacterial ligands bind host cell receptors - Interaction

can determine host cell specificity

Clinical Importance = Changing/blocking a ligand or its receptor can

prevent infection


The Nature of Infectious Disease Manifestations of Disease: Symptoms, Signs, and Syndromes

What are Symptoms ?

• Subjective characteristics of disease felt only by the

patient

What are Signs ?

• Objective manifestations of disease observed or

measured by others

What is a Syndrome ?

• Symptoms and signs that characterize a disease or

abnormal condition

Asymptomatic, or subclinical, infections lack symptoms but may

still have signs of infection

CONCEPT 14.21


The Nature of Infectious Disease

Etiology = Study of the cause of disease

• Diseases have various causes

CONCEPT 14.22


Find Causes of Disease Using Koch's postulates

• Robert Koch developed a set of postulates one must satisfy to

prove a particular pathogen causes a particular disease

CONCEPT 14.23

Exceptions to Koch's postulates

• Some pathogens can't be

cultured in the laboratory

• Diseases caused by a

combination of pathogens

and other cofactors

• Ethical considerations

prevent applying Koch's

postulates to pathogens that

require a human host


Virulence Factors of Infectious Agents

• Pathogenicity

• Ability of a microorganism to cause disease

• Virulence

• How easily the organism can cause disease

• Not about severity of the disease it causes but how easily it

causes disease

An organism (species or strain) is defined as being

pathogenic (or not), and depending upon conditions, may

exhibit different levels of virulence.

CONCEPT 14.24What is Pathogenicity and Virulence ?

What is the Difference between them ?


Figure 14.8 Relative virulence of some microbial pathogens.

Opportunistic pathogens

All are pathogenic

but less or more virulent

CONCEPT 14.24



1) Extracellular enzymes

• Secreted by the pathogen

• Dissolve structural chemicals in the body

• Help pathogen maintain infection, invade, and avoid body defenses

CONCEPT 14.25



2) Toxins are chemicals that harm tissues or trigger host immune responses

that cause damage

Two types of toxin are seen

1) Exotoxins 2) Endotoxins

Toxemia is a condition that refers to the presence of toxins in the

bloodstream and means the toxins are carried beyond the site of

infection.

CONCEPT 14.26


The Nature of Infectious Disease


3) Antiphagocytic factors

• Factors prevent phagocytosis by the host's phagocytic cells

• Allow pathogens to remain in a host for longer time

3a) Bacterial capsule

• Composed of chemicals not recognized as foreign

• Slippery and difficult for phagocytes to engulf

3b) Antiphagocytic chemicals

• Prevent fusion of lysosome and phagocytic vesicles

• Leukocidins directly destroy phagocytic white blood cells

CONCEPT 14.27


Figure 14.9c Some virulence factors.

Phagocytosis blocked by capsule

Capsule around

bacterium

Phagocyte

Capsule aroundbacterium

Bacteriareproduce

Phagocytic

vesicle

Lysosome

Incomplete phagocytosis

Antiphagocytic factors

2 main reasons why capsules block phagocytosis

1) They are Slippery

2) Hyaluronic acid or other normal body components seen in capsules

CONCEPT 14.27


The Nature of Infectious Disease • The Stages of Infectious Disease

• The disease process occurs following infection

• Many infectious diseases have five stages following infection

• Incubation period

• Prodromal period

• Illness

• Decline

• Convalescence

CONCEPT 14.28

ipidc


The Movement of Pathogens

Out of Hosts: Portals of Exit

• 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

CONCEPT 14.29


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

1) Contact transmission

2) Vehicle transmission

3) Vector transmission

CONCEPT 14.30


Modes of Infectious Disease Transmission

1) Contact Transmission

1a) Direct contact transmission

• Usually involves body contact between hosts

• Transmission within a single individual can also occur

1b) Indirect contact transmission

• Pathogens are spread from host to host by fomites (inanimate

objects – needles AIDS/hepatitis B)

1c) Droplet transmission

• Spread of pathogens in droplets of mucus by exhaling,

coughing, and sneezing

CONCEPT 14.31



Transmission

2) Vehicle Transmission

2a) Airborne transmission

• When pathogens travel more than 1 meter via an aerosol

• Aerosols can occur from various activities

• Sneezing, coughing, air-conditioning systems, sweeping

2b) Waterborne transmission

• Important in the spread of many gastrointestinal diseases

• Fecal-oral infection

CONCEPT 14.32



Transmission

2) Vehicle Transmission

2c) Foodborne transmission

• Spread of pathogens in and on foods

• Inadequately processed, cooked, or refrigerated foods

• Foods may become contaminated with feces

2d) Bodily fluid transmission

• Bodily fluids such as blood, urine, saliva can carry pathogens

• Prevent contact with conjunctiva or breaks in the skin or

mucous membranes

CONCEPT 14.32



Transmission

3) Vector Transmission (animals which transmit)

3a) Biological vectors

• Transmit pathogens and serve as host for some stage of the

pathogen's life cycle

• Biting arthropods transmit many diseases to humans

3b) Mechanical vectors

• Passively transmit pathogens present on their body to new

hosts

CONCEPT 14.33


Classification of Infectious DiseasesDiseases can be classified in a number of ways

• The body system they affect

• Taxonomic categories

• Their longevity and severity

• How they are spread to their host

• The effects they have on populations

CONCEPT 14.34


CONCEPT 14.35


So far we looked at Effect of pathogens on individuals

If studying effect of pathogens on populations - Epidemiology

Study of where and when disease occur and

how they are transmitted in populations

e.g. Study Frequency of Disease

CONCEPT 14.36


Epidemiology of Infectious Diseases

Study Frequency of Disease - Track occurrence of diseases

using two measures

1) Incidence

• Number of new cases of a disease in a given

area during a given period of time

2) Prevalence (always larger than incidence)

• Number of total cases (old and new) of a disease

in a given area during a given period of time

CONCEPT 14.37


Figure 14.14 Curves representing the incidence and the estimated prevalence of AIDS among U.S. adults.

CONCEPT 14.37


CONCEPT 14.38

Figure 14.15 Epidemiologists

report data in a variety of ways.

- to find patterns which may

give clues as to cause or cure


Figure 14.17 Epidemics may have fewer cases than nonepidemics.

Epidemic 1

Epidemic 2

Expected number of cases

Actual number of cases Disease A

Actual number of cases Disease B

Not about numbers but frequency CONCEPT 14.39


Figure 14.16 Illustrations of the different terms for the occurrence of disease.

Ebola ?

CONCEPT 14.39


CDC’s weekly Morbidity and Mortality Weekly Report

(MMWR)

reports on the number of cases of most of the

nationally notifiable diseases

Figure 14.18 A page from the MMWR.



How do they conduct Epidemiological Studies ?

3 methods - Descriptive/Analytical/Experimental

1) Descriptive epidemiology

Careful tabulation of data concerning a disease

• Record location and time of the cases of disease

• Collect patient information

• Try to identify the index case of the disease

CONCEPT 14.40



How do they conduct Epidemiological Studies ?

2) Analytical epidemiology

• Seeks to determine the probable cause, mode of

transmission, and methods of prevention

3) Experimental epidemiology

• Test a hypothesis concerning the cause of a disease

• Application of Koch's postulates

CONCEPT 14.40


Figure 14.19 A map showing cholera deaths in a section of London, 1854.

CONCEPT 14.40

• Record location

and time of the

cases of disease

• Collect patient

information

2 methods -

Descriptive/Analytical

• Seeks to determine

the probable cause,

mode of transmission,

and methods of

prevention


Figure 14.20 The interplay of factors

that result in nosocomial infections.CONCEPT 14.41



Hospital Epidemiology: Nosocomial Infections

Types of nosocomial infections

1) Exogenous

• Pathogen acquired from the health care environment

2) Endogenous

• Pathogen arises from normal microbiota due to factors

within the health care setting

3) Latrogenic (procedure/technique induced)

• Results from modern medical procedures

4) Superinfections

• Use of antimicrobial drugs reduces competition from some

resident microbiota – other microbes may thrive

CONCEPT 14.42


Epidemiology of Infectious DiseasesHospital Epidemiology: Nosocomial Infections

CONCEPT 14.43

Handwashing is the

most effective way to

reduce nosocomial

infections

Control of nosocomial

infections

Requires aggressive control

measures



Epidemiology and Public Health

1) Sharing of data among public health organizations

Agencies at the local, state, national, and global level share

information concerning disease

National - The United States Public Health Service

• National public health agency

• CDC is one branch

Global - World Health Organization (WHO)

• Coordinates public health efforts worldwide

CONCEPT 14.44


Epidemiology and Public Health

2) Role of public health agencies in interrupting

disease transmission

• Monitor water and food safety

• Work to reduce disease vectors and reservoirs

• Establish and enforce immunization schedules

• Locate and treat individuals exposed to contagious

pathogens

• Establish isolation and quarantine measures

CONCEPT 14.44

3) Public health education

• Public health agencies campaign to educate the public

on healthful choices to limit disease

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