Week 11

symptoms

• Subjective changes in body function that are felt by a patient as a result of disease

  • Not apparent to an observer

signs

Objective changes in a body that can be measured or observed as a result of disease

syndrome

A specific group of signs and symptoms that accompany a disease

pathology

The study of disease

etiology

The cause of a disease

pathogenesis

The manner in which a disease develops

infection

Invasion or colonization of the body by pathogens

infectious disease

• Occurs when an infection results in any change in the state of health

  • An infection may exist in the absence of a detectable disease

  • Disease may result when a particular type of microorganism locates in a part of the body where it is not normally found

communicable disease

• A disease that is spread from one host to another

  • Examples: COVID-19, chicken pox, measles, influenza, genital herpes, tuberculosis

contagious diseases

Diseases that are easily and rapidly spread from one host to another

noncommunicable disease

• A disease that is not spread from one host to another

  • Example: tetanus

duration

Average time that individuals have a disease from diagnosis until they are either cured or die

acute disease

Symptoms develop rapidly but has a short duration

chronic disease

Symptoms develop slowly, likely to last for a long period

subacute disease

Intermediate between acute and chronic

latent disease

Causative agent is inactive for a time but then activates and produces symptoms

severity

The presence and extensiveness of a disease in the body and its ability to cause death

asymptomatic (COVID-19)

No signs or symptoms

mild (COVID-19)

Fever, dry cough, tired, muscle pain, sore throat

moderate (COVID-19)

Breathlessness, tachycardia, persistent cough, higher fever

severe (COVID-19)

Pneumonia, extreme breathlessness, chest pain, high temperature, bluish lips/face

critical (COVID-19)

Severe acute respiratory syndrome (SARS), inflamed alveoli, may require ventilator

sepsis

Extreme inflammatory syndrome in response to severe infection

local infection

Pathogens are limited to a small area of the body

systemic (generalized) infection

An infection spread throughout the body by the blood and lymph

focal infection

Systemic infection that began as a local infection

sepsis

Toxic inflammatory condition arising from the spread of microbes, especially bacteria or their toxins, from a focus of infection

bacteremia

Bacteria in the blood

septicemia

Also known as blood poisoning; growth of bacteria in the blood; bacteria are proliferating in the blood

toxemia

Toxins in the blood

viremia

Viruses in the blood

primary infection

Acute infection that causes the initial illness

secondary infection

Opportunistic infection after a primary (predisposing) infection

subclinical infection

No noticeable signs or symptoms (inapparent infection, asymptomatic infection)

Koch’s postulates

• _____ are used to prove the cause of an infectious disease

• Exceptions to _____

  • Some pathogens can cause several disease conditions

  • Some pathogens cause disease only in humans

  • Some microbes have never been cultured

  • Several different pathogens may cause the same signs and symptoms

molecular Koch’s postulates

• Stanley Falkow - 1988

• Premise is not the ability to isolate a particular pathogen but rather to identify a gene that may cause the organism to be pathogenic

predisposing factors

• Variables that make the body more susceptible to disease or may alter the course of a disease

  • Nutrition

  • Sex

  • Genetic inheritance

  • Climate

  • Environment

  • Vaccination

  • Age

  • Lifestyle/behaviors

  • Compromised host

stages of disease

Incubation period → prodromal period → period of illness → period of decline → period of convalescence

incubation period

Interval between initial infection and first signs and symptoms

prodromal period

Short period after incubation; early, mild nonspecific symptoms

period of illness

Disease is most severe

period of decline

Signs and symptoms subside

period of convalescence

Body returns to its prediseased state; recovery

reservoirs

Continual sources of infection

human reservoirs

People with signs and symptoms

carriers

• May have inapparent infections or latent diseases

  • Asymptomatic carriers

  • Incubating carriers

  • Convalescent carriers

  • Chronic carriers

  • Passive carriers

zoonoses

Diseases primarily in wild and domestic animals that can be transmitted to humans

nonliving reservoirs

• Soil and water

• Foods

direct contact transmission

Requires close association between the infected and a susceptible host

congenital transmission

Transmission from mother to fetus or newborn at birth

indirect contact transmission

Spreads to a host by a nonliving object called a fomite

droplet transmission

Transmission via airborne droplets less than 1 meter

vehicle transmission

• Transmission by an inanimate reservoir

  • Airborne

  • Waterborne

  • Foodborne

    • May involve cross‐contamination (transfer of pathogens from one food to another)

vectors

• Arthropods, especially fleas, ticks, and mosquitoes

• Transmit disease by two general methods

  • Mechanical transmission

  • Biological transmission

mechanical transmission

Arthropod carries pathogen on its feet

biological transmission

Pathogen reproduces in the vector; transmitted via bites or feces

healthcare-associated infections (HAIs)

• Hospitals are a major reservoir for a variety of pathogens

• Also known as nosocomial infections

• Certain normal microbiota are opportunistic and pose a risk

• Antimicrobial resistance is high among _____

Clostridium difficile

Leading cause of HAIs

compromised host

Individual whose resistance to infection is impaired by disease, therapy, or burns

transmission of HAIs

• Direct contact transmission from hospital staff to patient or patient to patient

• Indirect contact through fomites and hospital ventilation system

  • Urinary catheters (fomite transmission)

  • Intravenous catheters

  • Respiratory aids

  • Needles

  • Surgical dressings

control of HAIs

• Reduce number of pathogens

  • Handwashing

  • Disinfecting tubs used to bathe patients

  • Cleaning instruments scrupulously

  • Using disposable bandages and intubation equipment

• Improve patients’ resistance to infection

  • Prescribe antibiotics only when necessary

  • Avoid invasive procedures

  • Minimize use of immunosuppressive drugs

• Infection control committees in hospitals oversee and monitor infection control

emerging infectious diseases

Diseases that are new or changing, increasing in incidence, or showing a potential to increase in the near future

antigenic shift

Two strains of influenza virus infect the same cell and the genomes get mixed; This makes a dramatically different virus

antigenic drift

Random mutations can occur within the cell that a virus infects, creating small changes in virus proteins

Escherichia coli and avian influenza

Contributing factor of emerging infectious diseases: genetic recombination between organisms

Vibrio cholerae

Contributing factor of emerging infectious diseases: evolution of existing organisms

antibiotic-resistant strains

Contributing factor of emerging infectious diseases: widespread use of antibiotics and pesticides

RNA viruses and antigenic shift/drift

Contributing factor of emerging infectious diseases: inherent genetic instability of some microbes

hantavirus

Contributing factor of emerging infectious diseases: changes in global climate and weather patterns

zika virus, chikungunya, and West Nile encephalitis

Contributing factor of emerging infectious diseases: modern transportation

Aedes aegypti and A. albopictus

Contributing factor of emerging infectious diseases: insect vectors transported to new areas where they become established

coccidioidomycosis

Contributing factor of emerging infectious diseases: ecological disaster, war, and expanding human settlement

diphtheria

Contributing factor of emerging infectious diseases: public health failure

pathogenicity

The ability to cause disease

virulence

The degree of pathogenicity

attenuation

• Weakening of the disease-producing ability of the pathogen

  • Attenuated vaccines contain crippled viruses or bacteria that are injected into a host to stimulate an immune response

portals of entry

• Mucous membranes

• Skin

• Parenteral route

  • Deposited directly into tissues when barriers are penetrated

  • Injections, bites, wounds, cuts, surgery

• Most pathogens have a preferred _____

ID50

• Infectious dose for 50% of a sample population

  • Measures virulence of a microbe

LD50

• Lethal dose for 50% of a sample population

  • Measures potency of a toxin

  • Virulence can be estimated from experimental studies

virulence factors

Once organisms enter a host, how do they cause disease?

examples of virulence factors

• Pili

• Enzymes that harm the host or prevent detection

• Proteins that disrupt normal cellular function

• Capsule

• Enzymes that inactivate antibiotics

pathogenicity island

A genomic island that contains virulence factors

adherence (adhesion)

Almost all pathogens attach to host tissues in a process called _____

adhesins (ligands)

_____ on the pathogen bind to receptors on the host cells

glycocalyx

_____ of Streptococcus mutans, made of dextran, enables the bacteria to adhere to teeth

fimbriae

_____ of Actinomyces adheres to the glycocalyx of S. mutans

viral spikes

_____ of SARS-CoV2 – adhere to ACE2 receptor on host cells

capsules

• Glycocalyx around the cell wall

• Impair phagocytosis

Streptococcus pneumoniae

pneumonia

Haemophilus influenzae

pneumonia and meningitis

Bacillus anthracis

anthrax

Yersinia pestis

plague

cell wall components

• M protein

• Opa protein

• Waxy lipid (mycolic acid)

M protein

• Resists phagocytosis

  • Streptococcus pyogenes

opa protein

• Allows attachment to host cells

  • Neisseria gonorrhoeae

waxy lipid (mycolic acid)

• Resists digestion by phagocytes

  • Mycobacterium tuberculosis

coagulases

coagulate fibrinogen forming fibrin

kinins

digest fibrin clots

hyaluronidase

digests hyaluronic acid, a host polysaccharide that hold cells together

collagenase

breaks down collagen