H. Microbiology - Principles of Disease & Epidemiology

Antimicrobial antagonism

normal microbiota prevent foreign strains of microorganisms from entering the body

Symbiosis

a relationship between 2 organisms where at least 1 organism is dependent on the other

Opportunistic pathogens

pathogens that do not cause disease in their normal habitat in a healthy person but may do so in a different environment; ex. - microbes that gain access through broken skin can cause infection
- can only cause disease in situations that compromise the host's defenses, such as the body's protective barriers, immune system, or normal microbiota

Mutualism

both organisms benefit (ex. - E. coli in intenstines)

Commensalism

A relationship between two organisms in which one organism benefits and the other is unaffected (ex. - S epidermis on skin, corynebacteria on eye surface, & mycobacteria in the ear and external genitalia)

Parasitism

one organism benefits and the other is harmed

Nosocomial infection

= Health-care associated infection (HAI); can be prevented with aseptic techniques, careful handling of contaminated material, frequent hand washing by staff, & staff education on infection control

What is a nosocomial infection?

hospital-acquired infection
- Caused by microorganisms in the hospital environment, compromised (weakened) status of host, & chain of transmission in hospital

Most common types of nosocomial infections

MRSA & aureus (staph infections) & C. difficile (causes colon inflammation)

Koch's postulates must be met __

in order to demonstrate that a specific microorganism is the cause of a specific disease

Koch's postulates (4 total)

1. same pathogen must be present in every case of the disease
2. pathogen must be isolated from diseased host and grown in pure culture
3. pathogen from culture must CAUSE disease when inoculated into healthy & susceptible lab animal
4. pathogen must again be isolated from inoculated animal and shown to be the same as original

Koch's postulates mnemonic

SIP CI (Same pathogen in every case, Isolated & grown in Pure culture, Cause disease in lab animal, Isolated and shown to be original pathogen)

Incidence

The number of people in a population who
develop a disease during a particular time period.
Indicates the spread of a diseases.

Epidemic

many people in a given area acquire a certain disease in a short period of time (ex. - influenza)

Endemic

disease that is constantly present (ex. - common cold)

Pandemic

worldwide epidemic

Sporadic

disease that occurs only occasionally

Focal infection

when a local infection enters the blood or lymph system and spreads to other parts of the body

Where does a focal infection start?

Usually starts as a local infection - when microorganisms are limited to a small area of the body

Herd immunity

when many people in a community are immune to a disease

How does herd immunity increase?

Increased by enough people in the community having the disease and developing protective antibodies against future infections OR by 95% community vaccination against a virus

Septicemia

infection in the blood; sepsis (toxic inflammatory condition that arises from the spread of bacteria) that results from pathogens in the BLOODSTREAM

Bacteremia

presence of bacteria in the blood

Viremia

presence of viruses in the blood

Reservoir of infection

a continual source of the organisms that cause a disease; can be living or an animate object as long as conditions are right for the organisms to survive

How do humans act as reservoirs of infection?

people have pathogens within their bodies that can be transmitted either directly or indirectly, people w/ signs and symptoms of disease can transmit disease, carriers - people who harbor a pathogen and transmit it to others even though they have no signs/symptoms

How do animals act as reservoirs of infection?

Zoonoses - diseases that occur mainly in wild or domestic animals but that may be transmitted to humans via direct contact with infected animals or pet waste; contamination of food and water; insects; contaminated hides, fur, or feathers; consumption of infected animal products

Fomite

a nonliving object (such as a glass, tissue, towel, money. etc.); the disease is transmitted from the reservoir of infection to the host by way of the fomite

Acute disease

a disease that develops rapidly, but only lasts a short time (for example, influenza)

Chronic disease

develops more slowly; the body reactions are often less severe but it is continuous or recurrent for long periods of time (examples - mononucleosis, tuberculosis, hepatitis B)

Primary infection

an acute infection that causes initial illness; Body has no defenses built up to disease

4 pathogens that cause primary infections

viruses, bacteria, fungi, parasites

Secondary infection

caused by a pathogen after a primary infection has weakened the body's defenses

Symptoms

Subjective characteristics of disease felt only by the patient (changes in body function such as pain and malaise→ may not be apparent to an observer)

Signs

objective changes that a doctor can measure; includes lesions, swelling, fever, and paralysis

Emerging infectious disease (EID)

new or changing diseases that show an increase in incidence in the recent past or a potential increase in the future; Can be caused by a virus, bacterium, fungus, or protozoan

How do most EIDs form?

Most are zoonoses, mainly viral, usually transmitted via a vector (insects, etc.)

Factors that contribute to emergence of new infectious disease

Genetic recombination
Evolution of existing microorganisms
Antibiotic-resistant bacteria
Global warming
Spread to new geographic areas by modern transportation
Natural disasters
Increase in animal populations
Failure of public health measures (vaccine boosters)

Transmission of a disease occurs when

agent leaves its reservoir or host through a portal of exit, is conveyed by some mode of transmission, and enters through an appropriate portal of entry to infect a susceptible host → this sequence is sometimes called chain of infection

3 forms of contact transmission

direct, indirect, droplet

Direct contact transmission

person-to-person transmission; the direct transmission of an agent by physical contact between disease source and host (ex. - kissing, handshaking, bites, sexual intercourse)

Indirect contact transmission

spreads to a host by a fomite (nonliving host)

Droplet transmission

transmission via airborne droplets of respiratory or salivary secretions less than 1 meter

Vehicle transmission

spread of pathogens via inanimate reservoirs such as food, water, or blood; can also be on blood or other body fluids, drugs, or IV fluids

Vector transmission

transmission of an infectious agent from 1 host to another by an insect, arthropod, or anima; can be mechanical →passive transport of pathogens on the insect's feet or other body parts. If the insect makes contact with the host's food, pathogens can be used transferred to the food & later swallowed by the host

Latent infection

a pathogen is inactive for a time but then becomes active to produce symptoms (ex. - shingles)

5 stages of an infectious disease

incubation, prodromal, illness, decline, convalescence

Incubation period

interval between initial infection and first signs and symptoms

Prodromal period

short period after incubation; early, mild symptoms

Period of illness

most severe signs and symptoms

Period of decline

signs and symptoms subside

Period of convalescence

body returns to its prediseased state