Chapter 11 Study Guide

Colonization

Microbes present in the host but do not cause disease

Infection

Microbes get past host defenses, enter tissues, and multiply → produces inflammation

Disease

The effects of infection damage or disrupt tissues and organs

Infectious disease

A pathologic state caused directly by microorganisms or their products

Commensalism

Microbes benefit; host is unaffected

Example: E. coli in the intestine

Mutualism

Both organisms benefit

Example: Bacteria in the stomachs of cows

Parasitism

Pathogen damages the host; may result in disease

Example: ticks

Types of parasites

Obligate, facultative, endoparasite, extoparasite

Obligate parasite

Requires a host

Facultative parasite

Can be free-living and then use a host

Endoparasites

Live inside a host

Ectoparasites

Live outside the host

Sites where normal biota found in humans

Skin, upper respiratory tract, GI tract, outer urethra, external genitalia, vagina, external ear canal, conjunctiva

Factors that weaken host defenses

Old age or extreme youth, genetic or acquired immune defects, surgery or organ transplants, underlying disease, chemotherapy or immunosuppressive medications, physical or mental stress, pregnancy, other infections

5 sources where newborns acquire microbiota

In utero, birth, milk, caregives, environment

Pathogenicity

The potential of a microorganism to cause disease

Virulence

Determined by a microorganism’s ability to establish itself in a host and cause damage

Steps for a microbe to cause disease

Find a portal of entry → attach to host cells → survive host defenses → cause damage → exit the host

Polymicrobial infections

Infectious involving more than one organism, so an initial infection can be associated with another infection

Portals of entry

Skin, GI tract, respiratory tract, urogenital tract, parenteral route, endogenous biota

Portals of exit

Skin cells or open lesion, fecal matter, respiratory secretions, urogenital secretions, blood, salivary gland secretions

Infectious Dose (ID)

The minimum number of microbes necessary for an infection to proceed. A smaller infectious dose → greater virulence

3 Ways microbes can cause tissue damage

Enzymes or toxins, excessive or inappropriate host response, and epigenetic changes

Exoenzymes

Enzymes secreted by microbes that break down and damage host tissues or dissolve protective barriers, allowing disease to spread

Examples: mucinase, hyaluronidase, coagulase, kinase

Mucinase

Digests the protective coating on mucous membranes

Hyaluronidase

Digests the substance that cements animals cells together

Coagulase

Causes clotting of blood or plasma

Kinase

Dissolves fibrin clots

Exotoxins

Small proteins secreted from either gram-postive or gram-negative bacterial cells that becomes toxic in minute amounts and targets specific locations like nerves or intestines. Unstable in heat, can be converted into toxoids, stimulate the production of antitoxins, and do not usually cause fever

Endotoxin

Lipopolysaccharide (LPS) released from gram-negative bacteria through shedding or during cell lysis that are toxic in high doses and cause systemic effects like fever and inflammation. Stable in heat, cannot be converted into toxoids, do not stimulate antitoxins, and usually cause fever.

Exampels of exotoxins

Neurotoxins (nervous system), enterotoxins (intestines), hemotoxins (lyse red blood cells), and nephrotoxins (damage the kidneys)

Sign

Objective evidence of disease observed by another person

Symptom

Subjective evidence of disease experienced by the patient

Syndrome

A disease identified by a characteristic combination of signs and symptoms

Leukocytosis

Increased white blood cell levels

Leukopenia

Decreased white blood cell levels

Septicemia

Microorganisms multiply in the blood and are present in large numbers

Bacteremia

Bacteria present in the blood but are not mutiplying

Viremia

Viruses present in the blood but are not multiplying

Signs of a blood infection

Leukocytosis or leukopenia, septicemia, bacteremia, or viremia

Asymptomatic

An infection in which the microbe is active in host tissues but produces no noticeable symptoms

Pathogen

A microorganism whose relationship with the host is parasitic and results in infection and disease

Sequelae

Long-term or permanent damage to tissues or organs caused by an infectious disease

Examples: Meningitis → deafness, strep throat → rheumatic heart disease, lyme disease → arthritis, polio → paralysis

Virulence Factors

Characteristics, structures, or adaptations that contribute to a microbe’s ability to establish itself in a host and cause damage

Examples: fimbriae, capsules, surface proteins, leukocidins, enzymes, and toxins

5 Stages of Disease

Incubation period, prodromal stage, acute phase, convalescent period, continuation phase

Incubation period

Time from initial contact to first symptoms. Microbes multiply without causing enough damage for symptoms. Usually lasts 2-30 days in most cases

Prodromal Stage

Earliest noticeable symptoms, usually 1-2 days. Headaches, muscle aches, fatigue, upset stomach, and general malaise

Acute phase

Microbes multiply at high levels. Fever and specific signs and symptoms occur

Convalescent Period

Symptoms decline, and strength and health gradually return. Continue prescribed antibiotics as directed

Continuation Phase

Occurs in only some infections. Microbes may remain for months, years, or indefinitely, or symptoms may continue after the organism is gone

Reservoir

The primary habitat of a pathogen. Includes humans, animals, soil, water, and plants.

Human Reservoirs

Infected individuals or carriers who harbor pathogens

Animal Reservoirs

Animals that harbor pathogens capable of causing human infection

Soil and water reservoirs

Non-living environment reservoirs that contain microorganisms

Direct contact

Transmission through close contact between individuals

Indirect transmission

An object or substance carries an infectious agent

Vector transmission

Arthropdos harbor and transfer infectious agents to humans

Vertical transmission

An infectious agent passes from parent to offspring

Carrier

An individual who harbors an infectious agent and may serve as a source of infection

Asymptomatic carrier

Infected individual that shows no symptom of disease

Example: gonorrhea

Incubating Carrier

Spread the infectious agent during the incubation period

Example: infectious mononucleosis

Convalescent Carrier

Recuperating patient without symptoms but continues to shed viable microbes and convey the infection to others

Example: Hepatitis A

Chronic Carrier

Individuals who shelter the infectious agent for a long period after recovery because of the latency of the infectious agent

Example: Tuberculosis

Passive Carrier

Medical personnel that handle contaminated materials who risk mechanically or accidently transferring microbes to other patients

Example: Various HAIs

Horizontal Transmission

Disease spreads from one infected individual to another within a population; direct, indirect, and vector transmission

Healthcare-associated infection (HAI)

Also known as a nosocomial infection: acquired or devleoped during a hospital or healthcare facility stay.

Examples: Pneumonia, GI infections

Transmitter

The invidiual or object from which an infection is acquired

Zoonosis

An infection naturally found in animals that can be transmitted to humans

Communicable

A disease in which an infected host can transmit the agent to another host and establish infection

Contagious

A highly communicable disease, especially through direct contact

Noncommunicable

An infectious disease that is not transmitted from one host to another

;Epidemiology

The study of the frequency and distribution diseases and other health-related factors in defined populations

Goals of Epidemiology

Identify the causative agents of disease, investigate sources and mode of transmission, trach behaviors such as exercise and smoking, study disease pathology, and track the number and distribution of cases in communities

How epidemiology differs from traditional medical practice

Epidemiology focuses on disease patterns in populations; studies the frequency, distribution, and transmission; and investigates factors affecting community health

Notifiable or reportable disease

A disease that must be reported to public health authorities

Example: anthrax

Incidence

Number of new cases during a specific time period. Measures the occurrence of new disease. Usually reported per 100,000 susceptible individuals

Prevalence

Total existing cases in a population. Provides a snapshot of disease burden. Can be expressed as a percentage

Index case

The first case that brings an epidemic to the attention of public health officials

Endemic

An infectious disaese that occurs at a relatively steady frequency over a long period in a particular geographic area

Sporadic

Occasional disease cases appearing at irregular intervals and random locations

Epidemic

An increase in disease occurence beyond what is expected for a population

Pandemic

An epidemic that spreads across continents

Mortality Rate

Measures deaths in a population due to a particular disease

Morbidity rate

Measures the occurrence of illness in a population