Final Exam Key Concepts: Infections, Immunity, and Epidemiology

Human microbiome

The collection of microorganisms living in and on the human body that influence health, digestion, immunity, and metabolism.

Normal biota

Microbes normally present in or on the body that typically do not cause disease but can protect the host or become opportunistic pathogens.

Portal of entry

The route by which a microbe enters a susceptible host (e.g., skin breaks, mucous membranes, respiratory tract).

Portal of exit

The route by which a pathogen leaves the host (e.g., respiratory droplets, blood, body fluids, feces).

Adhesion (attachment to host cells)

The process by which microbes bind to host cell receptors using structures like fimbriae or capsules.

Surviving host defenses

Evading or resisting the host’s immune defenses to establish infection.

Virulence

The degree to which a pathogen can cause disease; a measure of its potency.

Pathogenicity

The ability of an organism to cause disease in a host.

Pathogenesis

The sequence of events and mechanisms by which a disease develops.

Endotoxin

A lipopolysaccharide component of Gram-negative bacteria (lipid A) released upon cell death that triggers strong inflammatory responses.

Exotoxin

Toxin secreted by bacteria that can cause damage to host cells; often highly potent and immunogenic.

Latency

A period when a pathogen is present but inactive or not causing symptoms, with possible reactivation later.

Sequelae

A condition resulting from a disease or injury that persists after the acute phase.

Sign

An objective finding observed by others (e.g., fever, rash).

Symptom

A subjective experience reported by the patient (e.g., pain, fatigue).

Syndrome

A group of signs and symptoms that characterize a particular disease.

Subclinical / asymptomatic

An infection or disease with no noticeable symptoms; may still be transmissible.

Incubation period

Time between infection and the first appearance of symptoms.

Prodromal stage

Early, nonspecific symptoms that precede the full-blown illness.

Acute phase

Period of most intense symptoms of a disease.

Convalescent period

Recovery phase as the patient regains health.

Continuation period

Phase after the acute illness when some symptoms may persist or recur.

Reservoir

Any natural habitat where a pathogen Live and multiplies (humans, animals, environment).

Transmitter

Agent or mechanism that conveys a pathogen from reservoir to host.

Carrier

A person or animal that harbors a pathogen without showing symptoms but can transmit it.

Zoonosis

A disease that can be transmitted from animals to humans.

Direct transmission

Immediately person-to-person transmission (touch, droplet spread).

Indirect transmission

Transmission via a intermediary (fomites, vehicles, or vectors).

Mechanical transmission

Passive transfer of a pathogen by a vector or object without replication in the vector.

Biological transmission

Transmission involving a pathogen that multiplies within a vector before transfer.

Nosocomial infections

Healthcare-associated infections acquired in a hospital or other healthcare setting.

Top 3 nosocomial infections

Urinary tract infections, pneumonia, and surgical-site infections are the most common nosocomial infections.

Koch’s postulates

Four criteria to establish a causative relationship between a microbe and a disease: (1) microbe in diseased, (2) isolate in pure culture, (3) cause disease when introduced to a susceptible host, (4) re-isolate the microbe from the newly diseased host.

Prevalence

The total number of cases of a disease in a population at a given time.

Incidence

The number of new cases of a disease that develop in a population during a specific time period.

Epidemiology

The study of how diseases distribute and what determines their distribution in populations.

Epidemic

A rapid and widespread increase in the number of cases of a disease in a population.

Endemic

A disease that is consistently present in a population or geographic area at a baseline level.

Sporadic

Cases occur irregularly and infrequently in a population.

Pandemic

An epidemic that spreads across large geographic areas, often globally.

MRSA

Methicillin-resistant Staphylococcus aureus; a Staphylococcus aureus strain resistant to many beta-lactam antibiotics.

Measles

A highly contagious viral disease with fever, cough, conjunctivitis, and a characteristic rash; preventable by vaccination.

Impetigo

A contagious bacterial skin infection (usually Staphylococcus aureus or Streptococcus) causing crusted lesions.

Chickenpox/Shingles

Varicella-zoster virus infection; chickenpox in children (rash, fever); reactivation causes shingles.

Ringworm (Tinea infections)

Fungal dermatophyte infections of skin, hair, or nails; not a worm; various body-site names (tinea corporis, capitis, etc.).

Conjunctivitis

Inflammation of the conjunctiva (pink eye); can be bacterial or viral; contagious.

Meningitis

Inflammation of the meninges surrounding the brain and spinal cord; causes include Neisseria meningitidis among others.

Neonatal meningitis

Meningitis occurring in newborns, often due to Group B Streptococcus or E. coli.

Encephalitis

Inflammation of the brain; usually viral; causes fever, headache, altered mental status.

Rabies

A viral encephalitis transmitted by animal bites; nearly always fatal without post-exposure vaccination.

Tetanus

Clostridium tetani infection causing muscle rigidity and spasm; preventable by vaccination.

Botulism

Caused by botulinum toxin from Clostridium botulinum; leads to flaccid paralysis; three types: foodborne, infant, wound.

Malaria

Parasitic disease caused by Plasmodium spp. transmitted by Anopheles mosquitoes; fever cycles and flu-like symptoms.

Sepsis

A life-threatening organ dysfunction caused by a dysregulated host response to infection.

Lyme disease

Infection with Borrelia burgdorferi transmitted by Ixodes ticks; early rash (erythema migrans) and flu-like symptoms.

Pharyngitis

Sore throat; can be viral or bacterial (e.g., Streptococcus pyogenes); diagnosis and treatment vary.

Acute Otitis Media

Acute middle-ear infection common in children; ear pain, fever; often follows a viral URI.

Community-Acquired vs Hospital-Associated Pneumonia

CAP occurs outside hospitals; HAP occurs 48 hours after admission and is not incubating on admission; different pathogens and management.

RSV (Respiratory Syncytial Virus)

A common viral pathogen causing bronchiolitis and pneumonia, especially in infants and young children.

Tuberculosis (primary, secondary, extrapulmonary)

Infection by Mycobacterium tuberculosis; primary TB, reactivation TB (secondary), and TB outside the lungs (extrapulmonary).

Acute diarrhea

Sudden onset of frequent loose stools; often caused by Campylobacter jejuni or Clostridioides difficile among others.

Chronic diarrhea

Prolonged diarrhea lasting weeks or more; can be due to diverse bacterial, viral, parasitic, or inflammatory causes.

Gastritis and gastric ulcers

Inflammation of the stomach lining and ulcers, commonly associated with Helicobacter pylori infection.

Hepatitis A

Viral hepatitis transmitted fecal-orally;