Chapter 15

What is the difference between a sign and a symptom?

A sign is an observable expression of disease, while a symptom is experienced or felt only by the patient.

What is a syndrome?

A combination of signs and symptoms that occur together.

What are sequelae?

The after-effects or long-term complications of a disease.

What does asymptomatic (subclinical) mean?

Having no noticeable signs or symptoms despite infection.

What is the difference between an infectious and a non-infectious disease?

Infectious diseases are caused by microorganisms or their toxins, while non-infectious diseases are caused by factors such as genetics or cancer.

What is the difference between communicable and contagious diseases?

Communicable diseases spread from host to host, while contagious diseases are especially easy to spread from person to person.

What is a zoonosis?

A disease transmitted from animals to humans.

What is an iatrogenic disease?

A disease caused by a medical procedure or treatment.

What is a nosocomial infection?

A hospital-acquired infection.

What are the six stages of disease?

Incubation, prodromal, invasive, acme, decline, and convalescence.

What happens during the incubation period?

The pathogen is present, but no signs or symptoms have appeared yet.

What occurs during the invasive phase of disease?

Typical signs and symptoms appear, and the disease reaches its greatest severity (acme).

What are Koch's four postulates?

The pathogen must be found in every case of the disease, isolated in pure culture, cause the disease in a healthy host, and be reisolated from the newly infected host.

What is pathogenicity?

The ability of an organism to cause disease.

What is virulence?

The degree or intensity of disease caused by a pathogen.

What factors determine a pathogen's pathogenicity?

Its ability to invade the host, multiply, and avoid host defenses.

What is the difference between a primary pathogen and an opportunistic pathogen?

Primary pathogens cause disease in healthy individuals, while opportunistic pathogens cause disease when host defenses are weakened or conditions change.

What are indigenous microbiota?

The normal microorganisms that live on or in the body without usually causing disease.

What are the main stages of pathogenesis?

Exposure (contamination), adhesion (colonization), invasion, infection/infestation, and disease progression.

What is an adhesin?

A protein or glycoprotein on a pathogen that allows it to attach to host cell receptors.

What is the difference between exotoxins and endotoxins?

Exotoxins are secreted toxins produced by bacteria, while endotoxins are components of Gram-negative bacterial cell walls released when cells break apart.

What are virulence factors?

Structural or physiological traits that help pathogens infect hosts and cause disease.

What is antigenic drift?

Small changes in viral surface proteins caused by point mutations.

What is antigenic shift?

A major change in viral surface proteins caused by gene reassortment, often when two influenza viruses infect the same host.

What is the ID50?

The median infectious dose required to infect 50% of a test population.

What is the LD50?

The median lethal dose required to kill 50% of a test population