Chapter 15: Understanding Infectious Diseases and Pathogen Mechanisms

Pathology

Study of disease

Etiology

Study of the cause of disease

Pathogenesis

Development of disease

Infection

Multiplication of any parasitic organisms

Disease

Disturbance in the state of health wherein the body can't carry out all of its normal functions

Signs of Disease

Objective and measurable; directly observed by a clinician

Symptoms of Disease

Subjective; felt or experienced by a patient but cannot be confirmed or measured

Syndrome

A specific group of signs and symptoms

Infectious disease

Caused by infectious agents

Noninfectious disease

Caused by some other factor - for example a poison

Communicable diseases

Can be spread from host to host - examples include measles and hepatitis

Non-communicable disease

Cannot be spread from host to host - examples include food poisoning and tetanus

Iatrogenic disease

Contracted as the result of a medical procedure

Nosocomial disease

Acquired in hospital settings

Zoonotic disease

Transmitted from animals to humans

Subclinical disease

No noticeable signs or symptoms (inapparent infection)

Acute disease

Symptoms develop rapidly

Chronic disease

Disease develops slowly

Subacute disease

Symptoms between acute and chronic

Latent disease

Disease with a period of no symptoms when the causative agent is inactive

Koch's Postulates

A set of criteria to establish a causative relationship between a microbe and a disease

Molecular Koch's Postulates

Premise is to identify a gene that may cause the organism to be pathogenic

Pathogenicity

Capacity to produce disease

Virulence

Intensity of the disease produced by the pathogen

Attenuation

Weakening of the disease-producing ability of the pathogen

ID50

Infectious dose for 50% of the test population

LD50

Lethal dose for 50% of the test population

Primary pathogen

Always causes disease

Opportunistic pathogen

Can only cause disease when the host's defenses are compromised

Virulence Factors

Molecules that enable pathogens to attach to host cells and cause disease

Adhesins

Molecules that bind to receptors on host cells

Biofilms

Communities of microorganisms that adhere to surfaces

Invasion

The dissemination of a pathogen throughout local tissues or the body.

Exoenzymes

Enzymatic virulence factors help bacteria invade tissue and evade host defenses.

Toxin

Substance that contributes to pathogenicity.

Toxigenicity

Ability to produce a toxin.

Toxemia

Presence of toxin in the host's blood.

Toxoid

Inactivated toxin used in a vaccine.

Antitoxin

Antibodies against a specific toxin.

Exotoxins

Proteins produced inside pathogenic bacteria, most commonly gram-positive bacteria, as part of their growth and metabolism.

Endotoxins

Lipid portions of lipopolysaccharides (LPS) that are part of the outer membrane of the cell wall of gram-negative bacteria.

Two-Subunit AB Toxins

A subunit is toxic. B subunit binds host cell receptors.

Primary infection

Acute infection that causes the initial illness.

Secondary infection

Opportunistic infection after a primary (predisposing) infection.

Local infection

Pathogens are limited to a small area of the body.

Systemic infection

An infection throughout the body.

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

Growth of bacteria in the blood.

Viremia

Viruses in the blood.

Antigenic variation

100 known serotypes of rhinovirus; each virus has a unique capsid protein.

Antigenic shift

Two strains of influenza virus infect the same cell and the genomes get mixed.

Antigenic drift

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

Latent Herpes Virus

Herpes virus goes into latency and incorporates its genome into the host cell.

Antigenic Masking

Some protozoans coat themselves in host antigens to avoid detection by the immune system.

Intracellular Location

Some protozoans have found ways to live inside the host cell to prevent detection.

Immunosuppression

Some protozoans induce the secretion of anti-inflammatory cytokines to reduce the innate immune response.