Infectious Disease Transmission and Epidemiology

Vocabulary flashcards reviewing infectious disease transmission, epidemiology concepts, disease staging, and bacterial mechanisms of pathogenicity.

Reservoir

The habitat of a pathogen where it can survive (living reservoirs like humans and animals, or non-living reservoirs like water and soil).

Symptoms

A subjective body function response felt by a patient as a result of a disease (e.g., fatigue).

Signs

Objective changes in a body that can be measured or observed by a medical professional as a result of a disease (e.g., fever).

Syndrome

A specific group of signs and symptoms used to characterize a condition (e.g., Irritable Bowel Syndrome).

Communicable Disease

A disease that is spread from one human host to another (e.g., influenza and chicken pox).

Noncommunicable Disease

A disease that is not spread from one human host to another, often involving microbes that live outside the body and only cause disease when introduced (e.g., tetanus).

Carrier

A living organism with a pathogen reproducing inside them and being shed into the environment, with symptoms ranging from none (asymptomatic) to obvious.

Direct Transmission

Person-to-person spread of a pathogen through physical contact (such as touch, kissing, or exchange of body fluids) without an intermediate host or object involved.

Droplet Transmission

Transmission of microbes via respiratory droplets over short distances ($<1\,\text{m}$) through sneezing and coughing.

Indirect Transmission

Transmission of a pathogen via a contaminated non-living item, referred to as a fomite.

Fomites

Inanimate, nonliving objects that become contaminated with pathogens (e.g., bedding, toys, surgical instruments, money, cups, and syringes).

Airborne Transmission

A vehicle transmission route where infectious agents begin in respiratory droplets but are dispersed via dust over distances $>1\,\text{m}$ from the initial reservoir.

Vectors

Living organisms, including arthropods (flies, ticks, mosquitoes) and vertebrates (dogs, rodents), that transfer a pathogen from one person to another.

Mechanical Transmission

Passive transport of a pathogen by a vector, such as when a fly carries a pathogen on its feet to food that is subsequently consumed by a human.

Biological Transmission

Active transport of a pathogen by a vector, such as when a mosquito bites an infected person, picks up the pathogen in blood, and injects it into a new host.

Epidemiology

The study of the occurrence, distribution, and determinants of health and disease in a population.

Descriptive Epidemiology

The collection and analysis of general data regarding disease occurrence in a population.

Analytical Epidemiology

The analysis of a particular disease to determine its probable cause.

Experimental Epidemiology

An approach that involves formulating a hypothesis and conducting controlled experiments, such as clinical trials with test and control groups.

John Snow

Epidemiologist who mapped the occurrence of cholera in London between 1848 and 1849.

Ignaz Semmelweise

Investigator who tested the theory from 1846 to 1848 that improved hand sterilization by doctors prior to exams would reduce the death rate.

Florence Nightingale

Pioneer who recorded in 1858 that individuals with a lower incidence of typhus were treated in hospitals with better sanitation.

Outbreak

The occurrence of numerous cases of a disease over a short period of time, often in an area where cases are typically minimal.

Incidence

The number of new cases of a disease during a particular time, serving as an indicator of the spread of disease.

Prevalence

The number of new and existing cases of a disease at a particular time, indicating how long a disease can persist in a population.

Endemic

A disease that is constantly present at a low incidence in a population (e.g., the common cold).

Epidemic

A disease that infects an unusually high number of individuals in a population (e.g., influenza).

Pandemic

A widespread, usually worldwide epidemic.

Common-source Epidemic

An epidemic originating from a contaminated common vehicle (such as food or water) characterized by a rapid increase in infected individuals over a short time period.

Human Host-to-Human Host Epidemic

An epidemic starting from an index case (patient zero) that spreads to susceptible hosts, showing a slow, steady progression followed by a gradual decline.

Incubation Period

The stage of disease progression representing the duration between the initial infection and the appearance of symptoms.

Prodromal Period

A short period following incubation characterized by low pathogen concentrations and mild symptoms.

Acute Period

The disease progression phase where the pathogen reaches highest concentrations and symptoms are severe.

Decline Period

The disease phase during which symptoms subside as pathogen levels decrease.

Convalescent Period

The final stage of disease progression during which the patient regains strength and returns to normal health.

Primary Infection

An initial infection that causes illness in a host.

Secondary Infection

An opportunistic infection that occurs after a primary infection.

Latent Disease

A disease in which the causative agent remains inactive or hidden for a period of time before activating to produce symptoms (e.g., shingles, tuberculosis).

Healthcare-associated Infections (HAIs)

Infections acquired while receiving treatment in a healthcare facility, affecting 1 in 38 hospital patients (2025 data).

Shiga Toxins

Toxins produced by enterohemorrhagic E. coli that target capillaries in the intestinal lining, inducing platelet clumping that damages red blood cells and can lead to kidney failure.

E. coli Strain O157:H7

The predominant enterohemorrhagic E. coli strain, where 'O157' designates the O antigen sugar composition of the LPS layer and 'H7' designates the specific flagellar protein.

Pathogenicity

The potential ability of a pathogen to cause disease in a host.

Virulence

The actual ability of a pathogen to infect or damage a host.

ID50

The number of microbes or viruses required to produce an infection in $50\%$ of healthy humans; a lower value indicates higher infectivity.

Adhesins

Surface molecules located on a pathogen's glycocalyx, fimbriae, or flagella that bind complementary receptors on host cells during adherence.

Phagocytosis

A host defense process in which immune cells recognize invading pathogen proteins, engulfing and destroying them.

Capsule

A thick polysaccharide layer formed around the bacterial cell wall inside a host that impairs TLR binding to PAMPs, preventing effective phagocytosis.

Coagulases

Bacterial enzymes produced by some Staphylococcus species that convert soluble fibrinogen into insoluble fibrin blood clots to shelter microbes from immune cells.

Kinases

Bacterial enzymes that digest fibrin clots to release trapped microbes into host tissues.

Antigenic Variation

The ability of certain microbes to alter their surface antigens so host antibodies can no longer recognize and bind to them.

Siderophores

Microbial proteins secreted into the environment to scavenge circulating iron ($\text{Fe}$) from the host and transport it back into the bacterial cell.

Exotoxins

Toxins produced inside bacterial cells and excreted into the surrounding environment, synthesized by both gram-positive and gram-negative bacteria.

Endotoxins

Toxins that constitute structural parts of the lipopolysaccharide (LPS) layer of gram-negative bacterial cell walls and are released upon cell damage.