Infection and Immunity Lecture Notes

Vocabulary flashcards covering the major terms and concepts discussed in the infection and immunity lecture.

Saprophytes

Free-living microbes that survive on dead or decaying organic matter; usually found in soil and water and rarely involved in human infectious disease.

Commensals (Normal Flora)

Microorganisms that live in harmony with the host without causing damage.

Pathogens

Microorganisms capable of producing disease in a host.

Pathogenicity

The ability of a microorganism to cause disease.

Primary (Frank) Pathogen

Organism that can cause disease in a previously healthy host with intact defenses.

Opportunist Pathogen

Organism that causes disease only when host defenses are impaired or compromised.

Infection

Lodgment and multiplication of an agent in host tissues; may or may not cause disease.

Primary Infection

Initial infection of an organism in a host.

Reinfection

A subsequent infection in the same host by the same organism.

Secondary Infection

Infection by a new agent in a host whose resistance is lowered by a pre-existing disease.

Local Infection

Infection confined to one specific area of the body.

Systemic Infection

Infection that spreads throughout the body.

Nosocomial Infection

Cross-infection acquired in a hospital setting.

Iatrogenic Infection

Physician-induced infection resulting from investigative, therapeutic, or other medical procedures.

Inapparent (Subclinical) Infection

Infection with no obvious clinical symptoms.

Atypical Infection

Infection lacking the typical clinical manifestations of the disease.

Latent Infection

Persistence of an organism in tissues in a hidden form, producing disease when host resistance falls.

Carrier

Person who harbors a pathogen without showing symptoms.

Convalescent Carrier

Individual recovered from disease but still harboring large numbers of the pathogen.

Healthy Carrier

Individual who harbors the pathogen but is clinically well.

Incubatory Carrier

Individual incubating the pathogen in large numbers but not yet ill.

Temporary Carrier

Carrier state lasting less than six months.

Chronic Carrier

Person harboring a pathogen for months, years, or life.

Contact Carrier

Person who acquires the pathogen directly from a patient.

Paradoxical Carrier

Carrier who acquires pathogens from another carrier.

Reservoir Host

Animal or insect that maintains a pathogen in nature and serves as a source of infection.

Zoonosis

Disease transmissible from animals to humans.

Vector

Arthropod or other living carrier that transmits an infectious agent to a susceptible host.

Mechanical Vector

Vector that transmits pathogens without the agent multiplying or developing within it.

Biological Vector

Vector in which the pathogen multiplies or undergoes development before transmission.

Extrinsic Incubation Period

Interval between pathogen entry into a vector and the vector becoming infective.

Fomite

Inanimate object that conveys infectious agents between individuals.

Droplet Nuclei

Tiny airborne particles that transmit respiratory pathogens during inhalation.

Inoculation Transmission

Direct introduction of a pathogen into skin or mucosa (e.g., by bites, needles).

Vertical (Congenital) Transmission

Passage of pathogens from mother to fetus across the placenta.

Attenuation

Reduction of virulence of a microorganism.

Virulence

Relative ability or degree with which a microbe causes disease.

Adhesins

Bacterial surface ligands that mediate specific attachment to host cell receptors.

Invasiveness

Ability of a pathogen to spread within host tissues after infection is established.

Exotoxin

Heat-labile, highly potent protein toxin secreted by bacteria; can be converted to toxoids.

Endotoxin

Heat-stable lipopolysaccharide component (lipid A) of gram-negative outer membranes released on cell lysis.

Capsule

Slippery mucoid layer around some bacteria that inhibits phagocytosis.

Streptococcal M Protein

Surface protein of Streptococcus pyogenes that resists phagocytosis.

Antigenic Variation

Change in surface antigen composition during infection to evade immune responses.

Serum Resistance

Ability of bacteria to resist complement-mediated lysis in blood.

Siderophore

Bacterial molecule that scavenges iron from host iron-binding proteins.

Coagulase

Staphylococcal enzyme that forms a fibrin barrier to inhibit phagocytosis.

Lecithinase-C

Clostridium perfringens enzyme that damages tissues and promotes spread of infection.

Collagenase

Enzyme that breaks down collagen, aiding bacterial invasion (e.g., C. perfringens).

Hyaluronidase

Enzyme that splits hyaluronic acid, facilitating spread through tissue spaces.

Streptokinase (Fibrinolysin)

Streptococcal enzyme that dissolves fibrin clots, promoting spread of infection.

Cytolysins

Toxins, such as hemolysins and leukocidins, that destroy red or white blood cells.

IgA1 Protease

Bacterial enzyme that cleaves protective IgA at mucosal surfaces.

Plasmid

Extrachromosomal DNA element carrying genes such as antibiotic resistance (R-factors).

Communicability

Ability of a microbe to spread from one host to another.

Infective Dose (ID50)

Quantity of organisms required to infect 50 % of exposed hosts under defined conditions.

Bacteremia

Presence of bacteria circulating in the bloodstream.

Septicemia

Condition where bacteria multiply in blood, produce toxins, and cause high swinging fever.

Pyemia

Septicemia with multiple abscesses in internal organs caused by pyogenic bacteria.

Endemic

Disease constantly present in a particular geographic area.

Epidemic

Disease that spreads rapidly, affecting many individuals in an area simultaneously.

Pandemic

Epidemic that spreads worldwide, involving very large numbers of people.