Microbiology Chapter 14: Principles of Disease

Pathology

scientific study of disease

What 3 things does pathology include the study of

Etiology

Pathogenesis

Clinical significance

Etiology

cause or origin of disease

Pathogenesis

the manner in which the disease develops, progresses, maintains after it is caused

Clinical significance

Structural + functional changes brought about by disease + effects on the body

Symptom

subjective changes that are not apparent to the observer

not measureable

ex. pain, fatigue, malaise

Definition of sign

objective changes that are measurable

ex. fever, lesions, swelling

Definition of syndrome

a specific group of symptoms or signs that may always accompany a particular disease

Local infection

microbe enters the body and remains confined to specific tissues / small areas

ex. boils, lesions

Systemic infection

Spread of infection, usually through the bloodstream

ex. viral diseases (chickenpox, HIV/AIDS)

Definition of primary infection

The acute infection that causes the initial illness

Definition of secondary infection

caused by an opportunistic pathogen (something normally harmless or mild)

occurs after the primary infection weakens the body's defenses

Characterization of normal microbiota

microorganisms that colonize the body but do not produce disease under normal conditions

Benefits of normal microbiota

Serve protective function

More developed immune system

Microbial antagonism

Definition of microbial antagonism

Normal microbiota protect against colonization by pathogens

by competing for nutrients and producing harmful substances (bacteriocins) to kill / inhibit growth

Symbiosis

The relationship between two organisms where one organism is dependent on the other

Commensalism

one organism benefits, other unaffected

Mutualism

both organisms benefit

Parasitism

one organism benefits at expense of other

What does it mean for a microorganism to be opportunistic?

microorganism ordinarily does not cause disease

but may do so if in different environment or if host is compromised

(causing opportunistic infections)

What is an example of an opportunistic microorganism?

E. coli causing UTIs and pulmonary infections but harmless in large intestine

Why are Koch's Postulates significant?

standard for determining the causative agent in the germ theory of disease

Koch's Postulate 1

the same pathogen must be present in every case of the disease

Koch's Postulate 2

the pathogen must be isolated from the diseased host and grown in pure culture

Koch's Postulate 3

the isolated pathogen must be used to inoculate a healthy lab animal and must cause the same disease

Koch's Postulate 4

the same pathogen must be re-isolated from the new host and must be shown to match the first pathogen

Acute disease

develops rapidly but lasts only a short time

ex. the flu

Chronic disease

Develops more slowly

likely to continue for longer periods or recur

Signs and symptoms may be less severe

ex Mononucleosis, hep B

Sepsis (septicemia?)

presence of a toxin or microbe in the blood or tissue

Bacteremia

presence of bacteria in the blood

Viremia

presence of viruses in the blood

Toxemia

presence of toxins in the blood

Explain "human reservoir"

the human body is the principal living reservoir of human disease

includes symptomatic individuals and asymptomatic carriers

Ways diseases can be transmitted

direct contact (physical contact)

indirect contact (fomites)

droplet transmission

vehicle transmission

vectors

Definition of zoonoses

diseases that occur in animals (animal reservoirs) that can be transmitted to humans

What are examples of nonliving reservoirs?

soil and water

Direct contact transmission

Person-to-person transmission

Physical contact b/w source and host (no intermediate object)

Most commonly through touching, kissing, sex

Indirect contact transmission

from nonliving object (fomite) reservoir to host

ex. cups, tissues, doorknobs, stethoscope

Droplet transmission

microbes spread in droplet nuclei (mucus droplets)

travel short distances (less than 1 meter)

through sneezing, coughing, laughing, talking

Vehicle transmission

transmission via non-living medium

ex food, water, air, body fluids (blood)

Air vehicle transmission

Spread of disease through droplet nuclei in dust

travelling over 1 meter

ex. fungal spores

Vector + ways

animals that carry pathogens

mechanical transmission + biological transmission

Mechanical transmission

passive transport of pathogens on the insect's feet/body parts

lands on food which is consumed by host

Biological transmission

pathogen reproduces in the vector

ex. Plasmodium vivax

Incidence

number of people who develop a disease during a particular time period (new cases only)

indicator of spread of disease

“water flowing into a tub”

Prevalence

number of people who have a disease at a specific time regardless of when it first appeared

Includes all existing (both old and new) cases

Indicator of seriousness and how long a disease affects population

“water level sitting in tub”

Nosocomial infections

infections that are hospital-acquired

aka Healthcare Associated Infections (HAIs)

Nosocomial infection numbers

Acquired by 5-15% of hospital patients

Three factors in nosocomial infections

presence of microorganisms in hospital

compromised host

chain of transmission

(interaction of all 3 factors more likely to cause HAI)

Definition of a compromised host

an individual impaired by disease, therapy, or burns

Principal conditions compromising a host

having broken skin/mucous membranes

suppressed immune system

HAIs chain of transmission principal routes

direct contact (staff-patient or patient-patient)

indirect contact (fomites like catheters, needles, ventilation system)