Chapter 14: Infection, Infectious Disease, and Epidemiology

Infection

condition where pathogenic microbes penetrate host defenses, enter tissues, and multiply

Disease

any deviation from health, disruption of a tissue or organ

Infectious Disease

an infection that results in disease

Signs

objective evidence of disease

Symptoms

subjective effect of the disease

Communicable/contagious disease

infectious disease that spread from one host to another

Pathogens

parasitic microbes whose relationship with a host results in infection and disease

True pathogens

capable of causing disease in healthy persons

Opportunistic pathogens

cause disease when host's defenses are compromised or microbe is introduced into an unusual location

Localized infection

microbe is limited to a small area

Systemic infection

infectious disease is disseminated throughout the body

Primary infection

initial infection

Secondary infection

additional infection that occurs as a result of the primary infection

Course of infectious disease

1. Incubation period

2. Prodromal phase

3. Illness

4. Decline

5. Convalescence

Incubation period

time between introduction of microbe to host and onset of illness

Prodromal phase

early, vague symptoms, malaise, headache

Illness

most severe stage, pathogen replicating at highest rate

Decline

Immune response peaks at this period, body gradually returns to normal

Convalescence

stage of recuperation and recovery

Chronic carriers

have no signs or symptoms of disease but are contagious

Infectious Dose

minimum number of microbes necessary to establish an infection

Infectious dose of measles

1 virion

Infectious dose of cholera

100,000,000 cells

Portal of Entry

characteristic route a microorganism follow to enter the tissues of the body

Examples of portals of entry

skin and mucous membranes

Vertical Transmission

the transfer of disease or infection from a parent to their child during pregnancy, childbirth, or breastfeeding

STORCH

Syphilis, toxoplasmosis, other (listeriosis), rubella, cytomegalovirus, herpes

Adhesion

how microorganisms attach themselves to cells

Examples of adhesion factors

fimbriae, flagella, biofilms, cilia, spikes

Adherence E. coli strains

normal microbiota, strains that cause UTIs, and diarrhea causing strain

Normal microbiota E. coli

adhesin allows them to adhere to cells that line large intestine

UTI E. coli strain

have unique fimbriae that allow them to attach to bladder

Diarrhea-causing strain of E. coli

have unique fimbriae that allow them to attach to cells of small intestine

3 ways of avoiding immune system detection

biofilms, hiding within a host cell, and antiphagocytic factors

coagulase

enzyme that causes microscopic blood clots to hide bacteria

glycocalyx/capsule/slime layer

composed of chemicals normally found in the body to hide the bacteria

exoenzymes

can damage host cells and tissues and allow bacteria to invade tissues/cells

streptokinase

dissolve fibrin clots and allows dissemination of the bacteria

hyaluronidase

enhances pathogen penetration through tissues by dissolving ECM in connective tissue or collagen

exotoxins

extracellular toxins that are secreted by bacterium or leak following lysis

3 types of exotoxins

cytotoxins, enterotoxins, and neurotoxins

cytotoxins

generally kill cells or affect their function

enterotoxins

affect cells lining the gastrointestinal tract

neurotoxins

affect conduction of nerve impulses, interfere with neuromuscular activity

endotoxin

Lipid A of the outer membrane of certain gram-negative bacteria that is released only when the bacteria die.

Chain of Infection

reservoir of infectious agent, portal of exit, transmission, portal of entry, susceptible host

reservoirs of infection

sites where pathogens are normally maintained as a source of infection

Types of reservoirs

Animal, human, non-living

Source

individual or object from which an infection is actually acquired

Non-living reservoirs

soil, water, food

Zoonoses

diseases that spread naturally from animal hosts to humans

Vectors

Animals that carry pathogens from person to person

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

shows no symptoms

Incubation carriers

spread the infectious agent during the incubation period

Convalescent carriers

recuperating without symptoms

Chronic carrier

individual who shelters the infection for a long period

Passive carrier

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

Portals of Exit

Routes through which pathogens leave the host.

Secretions

earwax, tears, nasal, secretions, saliva, sputum, respiratory droplets, vaginal secretions, semen, breast milk

excretions

feces & urine

Communicable disease

an infected host can transmit the infectious agent to another host

Non-communicable disease

does not arise through transmission from host to host

3 types of transmission

contact transmission, vehicle transmission, and vector transmission

Direct contact transmission

body contact between hosts

Indirect contact transmission

pathogen spread by fomite

fomite

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

vehicle transmission

spread of pathogens via air, drinking water and food, bodily fluids outside the body

airborne transmission

spread of pathogens farther than 1 meter

waterborne transmission

water is both reservoir and vehicle of transmission

food-borne transmission

The contamination of food or water with an organism that can cause disease.

blood fluid transmission

pathogen is spread through blood

biological vectors

Transmit pathogens and serve as host for some stage of the pathogen's life cycle

mechanical vectors

Passively transmit pathogens present on their body to new hosts

HAI

infection that an individual acquires while receiving treatment in a healthcare facility

nosocomial infection

hospital-acquired infection

Factors that result in HAI

presence of microorganisms in hospital environment, immunocompromised patients, transmission of pathogens between staff and patients and among patients

Normal microflora

organisms that live on or in the body but do not cause disease

Benefits of normal microflora

microbes in the digestive system produce enzymes that aid in digestion & help break down molecules humans can not metabolize on their own

Where are normal microflora found?

Skin, mouth, gastrointestinal tract, respiratory tract, urogenital tract, and eyes.

Major species of normal microflora

Lactobacillus, streptococcus, & escherichia

colonization of the newborn

recent research indicates that the intestines become colonized in utero. Babies continue to become colonized during the delivery process, feeding and during interactions with other individuals.