Chapter 13 - Microbe-Human Interactions Infection, Disease, and Epidemiology - Talaro Microbiology - NSU 251 (Estiandan)

Normal resident microbiota / commensals

microbes that engage in mutual or commensal associations with humans

Infection

microbe that has penetrated the host defenses, invaded sterile tissue, and multiplied

Disease

damage to host, any deviation from health

pathogen

disease causing microorganism

the uterus and contents are

normally sterile and remain so until just before birth

initial colonization of the newborn

Breaking of fetal membrane exposes the infant; all subsequent handling and feeding continue to introduce what will be normal flora

major factors that weaken host defenses and increase susceptibility to infection

old age and extreme youth

genetic defects in immunity and acquired defects in immunity

surgery and organ transplants

organic disease: cancer, liver malfunction, diabetes

chemotherapy/immunosuppressive drugs

physical and mental stress

other infections

Steps in the Development of an Infection

1) Finding a portal of entry

2) Attach firmly (to cell)/Adhesion

3) Invasion/Multiplication/Surviving host defense

4) Infection of target/Cause damage

5) disease

5) Exit host through portal of exit

portals of entry

characteristic route a microbe follows to enter the tissues of the body

exogenous agents

originate from source outside of the body

endogenous agents

already exist on or in the body

portal of entry - skin

nicks, abrasions, punctures, incisions

portal of entry - gastrointestinal tract

-contaminated food and drink

-fecal-oral transmission

-stomach pH, mucus, normal flora prevent infections

portal of entry - respiratory tract

oral and nasal cavities

portal of entry - urogenital tract

sexual contact, displaced organisms

Portal of entry: transplacental

- some pathogens exhibit vertical transmission

- spread from mother to developing child in utero

STORCH

Infection during pregnancy; vertical transmission; Syphilis, Toxoplasmosis, Other diseases (hepatitis B, AIDS and chlamydia), Rubella, Cytomegalovirus and Herpes simplex virus

Infectious Dose

the number of microorganisms or viruses sufficient to establish an infection

Adhesion

microbes gain a stable foothold at the portal of entry; dependent on binding between specific molecules on host or pathogen

Organelles or Parts that aid in attaching to a host

-Fimbriae

-Flagella

-Glycocalyx

-Cilia

-Suckers

-Hooks

-Barbs

-Viral spikes

Virulence factors

•traits used to invade and establish themselves in the host, also determine the degree of tissue damage that occurs - severity of disease

Virulence Factors for Infection in Chapter 13

Blocking phagocytosis, Invasion factors, Exoenzymes, Toxins

Phagocytes

A type of white blood cell that ingests invading microbes

antiphagocytic factors

used to avoid phagocytosis

leukocidins

produced by species of Staphylococcus and

Streptococcus, toxic to white blood cells; create pores in white blood cells and lead to lysis

Slime layer or capsule

makes phagocytosis difficult and imparts an ability to survive intracellular phagocytosis

Blocking phagocytosis and M. tuberculosis

Ability to survive intracellular phagocytosis

Invasion Factors

Some pathogens produce a secretion system to insert specialized virulence proteins directly into the host cells, ex. Salmonella

exoenzymes (extracellular enzymes)

(Mucinase, keratinase, collagenase, hyaluronidase, coagulase, strepto/sphaylokinase)

enzyme that is secreted by a cell and functions outside that cell

Toxigenicity

capacity to produce toxins at the site of multiplication

Endotoxin

A toxic component of the outer membrane of bacteria that is released only when the bacteria is damaged or dies; associated with certain gram-negative

Example of an endotoxin

LPS

Exotoxin

a toxin released by a living bacterial cell into its surroundings or into the infected tissue; have strong specificity

Examples of Exotoxins

hemolysins, A-B toxins

A-B Toxin

Exotoxin composed of an active subunit (A subunit) and a binding subunit (B subunit)

4 Stages of Clinical Infections

incubation period, prodromal stage, period of invasion, convalescent period

Incubation Period

time from initial contact with the infectious agent to the appearance of first symptoms; agent is multiplying but damage is insufficient to cause symptoms; several hours to several years

Prodromal Stage

vague feelings of discomfort; nonspecific complaints

Period of Invasion

multiplies at high levels, becomes well-established; more specific signs and symptoms

Convalescent Period

as person begins to respond to the infection, symptoms decline

Localized Infection

microbes enter the body and remains confined to a specific tissue

Systemic Infection

infection spreads to several sites and tissue fluids usually in the bloodstream

Focal Infection

when infectious agent breaks loose from a local infection and is carried to other tissues

Mixed Infection

several microbes grow simultaneously at the infection site - polymicrobial

Primary Infection

initial infection

Secondary Infection

another infection by a different microbe, succeeding a primary infection

Acute Infection

comes on rapidly, with severe but short-lived effects

Example of an Acute Infection

Common Cold

Chronic Infection

progress and persist over a long period of time

Examples of Chronic Infections

HIV, Herpes Simplex Virus type-2 - cold sores

signs of inflammation

redness, heat, swelling, pain, fever, soreness

edema

accumulation of fluid

granulomas and abcesses

walled-off collections of inflammatory cells and microbes in the tissues

lymphadenitis

swollen lymph nodes

leukocytosis

increase in the number of white blood cells

leukopenia

Abnormally low white blood cell count

septicemia

-microorganisms are multiplying in the blood and present in large numbers

bacteremia

bacteria in the blood; small numbers present in the blood, but not necessarily multiplying

viremia

viruses in the blood; usually in small numbers, but not necessarily multiplying

•Asymptomatic (subclinical) infection

although infected, the host doesn't show any signs of disease

Types of Portal of Exit

respiratory, skin scales, fecal exit, urogenital tract, open wounds, removal of blood

latency

infection in which the pathogen is not active or causes disease

chronic carrier

person with a latent infection who sheds the infectious agent

sequelae

long-term or permanent damage to tissues or organs

resevior

primary habitat in the natural world from which a pathogen originates

source

individual or object from which an infection is actually acquired

fomite

Any inanimate object to which infectious material adheres and can be transmitted.

carrier

•an individual who inconspicuously shelters a pathogen and spreads it to others; may or may not have experienced disease due to the microbe

asymptomatic carrier

someone who is infected with a disease organism but is not experiencing symptoms

passive carrier

contaminated healthcare provider picks up pathogens and transfers them to other patients

incubation carrier

spread the infectious agent during the incubation period

convalescent carrier

a person who recovers from a disease but continues to be a carrier

chronic carrier

an individual who shelters the infectious agent for a long period after recovery because of the latency of the infectious agent

communicable disease

when an infected host can transmit the infectious agent to another host and establish infection in that host

contagious

Able to be passed easily from one person to another.

non-communicable disease

infectious disease that does not arise through transmission from host to host; -Occurs primarily when a compromised person is invaded by his or her own normal microflora; -Contact with organism (facultative parasites, fungal/bacterial spores) in natural, non-living reservoir

direct contact

physical contact or fine aerosol droplets

indirect contact

passes from infected host to intermediate conveyor and then to another host

vehicle

Any substance that transmits microbes

airborne

droplet nuclei, aerosols

direct contact - communicable disease

contact, droplets, vertical, biological vector

indirect contact - communicable disease

fomites, food, water, biological products, air

nosocomial infection

an infection acquired during hospitalization

prevalence

•total number of existing cases with respect to the entire population usually represented by a percentage of the population

incidence

•measures the number of new cases over a certain time period, as compared with the general healthy population

mortality rate

the total number of deaths in a population due to a certain disease

morbidity rate

number of people afflicted with a certain disease

endemic

disease that exhibits a relatively steady frequency over a long period of time in a particular geographic locale

sporadic

when occasional cases are reported at irregular intervals

epidemic

when prevalence of a disease is increasing beyond what is expected

pandemic

epidemic across continents

Koch's Postulates

a sequence of experimental steps for directly relating a specific microbe to a specific disease