VET 401: Population Health, Epidemiology, and Disease Causation

Vocabulary flashcards covering core principles of epidemiology, disease measurement, causal inference frameworks, and outbreak investigation procedures from the VET 401 lecture series.

Quantitative Data

Numerical measurements that can be classified as either discrete (counts, such as flock size) or continuous (measurements along a continuum, such as age or weight).

Qualitative Data

Categorical data divided into nominative types (unordered categories or dichotomous states such as live/dead, ill/well, breed) and ordinal types (ordered ranking scales such as illness scores or body condition scores).

Ratio

A mathematical comparison of two mutually exclusive frequencies ($a:b$) where the numerator is not included in the denominator (e.g., disease odds of cases to non-cases); it cannot be interpreted directly as a probability statistic.

Proportion

A fraction in which the numerator ($a$) is included within the denominator ($a+b$), yielding a value from $0$ to $1$ that expresses probability or risk when multiplied by $100$.

Rate

A measure of the relationship between an event ($a$) and a defined population at risk evaluated over a specified time period ($x$), expressed as $\frac{a}{x}$ where $x$ represents population-time.

Population-Time

The sum of all disease-free time experienced by all individuals at risk in a study population, used as the denominator to estimate the rate of developing a disease outcome.

Crude Mortality

An outcome metric calculated as total deaths from all causes divided by the total population at risk of dying ($\frac{D}{A}$).

Cause-Specific Mortality

The mortality rate calculated as deaths from a specific disease $X$ divided by the total population at risk of death ($\frac{C}{A}$).

Case Fatality

The proportion of diagnosed cases of a specific disease $X$ that result in death ($\frac{C}{B}$, where $C$ is deaths from disease $X$ and $B$ is total cases of disease $X$).

Proportionate Mortality

The proportion of total observed deaths from all causes that is attributable to a specific disease $X$ ($\frac{C}{D}$, where $C$ is deaths from disease $X$ and $D$ is deaths from all causes).

Prevalence

A static cross-sectional measure representing the proportion of all existing cases (both old and new) in a defined population at a single point in time.

Incidence

The rate or risk of new cases developing within a susceptible population during a specified time interval, measuring the transition from disease-free status to diseased.

Risk Ratio (Relative Risk)

The ratio comparing the risk of disease in an exposed group to the risk of disease in an unexposed group, calculated as $\frac{a/(a+b)}{c/(c+d)}$.

Attributable Risk (Risk Difference)

The absolute difference in disease incidence or risk between an exposed group and an unexposed group ($\frac{a}{a+b} - \frac{c}{c+d}$), representing the excess risk directly attributable to the exposure factor.

Direct Causal Pathway

A relationship in which a pathogen directly causes disease without intermediate steps; the pathogen is both necessary and sufficient, meaning exposure always leads to identical disease manifestation in all individuals.

Indirect Causal Pathway

A multi-step causal mechanism where a pathogen produces disease through intermediate steps and interactions with other variables such as dose, route of exposure, age, and host immune status.

Epidemiologic Triad

A fundamental model of disease causation representing complex relationships and interactions between the agent, the host, and the environment.

John Snow's Broad Street Investigation

An 1850s cholera outbreak investigation in London that utilized contact tracing, household mortality rates, and a spot map to identify a contaminated public water pump as the point source, refuting miasma theory.

Spurious Correlation

A mathematical coincidence where two unrelated variables show strong statistical association over time without having any direct causal connection.

Koch's Postulates

An 1880 four-step framework to establish disease causation: 1) microorganism found in abundance in diseased but not healthy organisms; 2) isolated and grown in pure culture; 3) causes disease when introduced to a healthy host; 4) reisolated from the inoculated host and proven identical.

Bradford Hill Criteria (1964 Guidelines)

Nine guidelines used to evaluate epidemiological evidence for causation: temporality, strength of association, dose-response, experiment, consistency, biological plausibility, alternate explanations, specificity, and coherence.

Temporality

The essential causal guideline requiring that exposure to the suspected causal agent must precede the biological onset and clinical manifestation of disease.

Confounding

A distortion in the estimated association between an exposure and an outcome that arises when an extraneous third factor is independently associated with both the exposure and the outcome.

Rothman's Causal Pies

A multi-causal model conceptualizing sufficient causes of disease as complete pies comprised of individual slices representing component causes.

Necessary Cause

A component cause that must be present for disease to develop and is therefore a required component of every sufficient causal mechanism (pie).

Sufficient Cause

A complete causal mechanism or set of minimal conditions and component causes that inevitably produces a specific disease outcome.

Counterfactual Thinking

A theoretical concept in causal inference that evaluates what the disease outcome would have been in the exact same population if the exposure of interest had not occurred.

One Health

A collaborative, multisectoral approach recognizing the deep interconnections among human health, domestic and wild animal health, plant health, and their shared environments.

Herd Immunity

The indirect protection of susceptible individuals in a population that occurs when a sufficiently large proportion of the population is immune, thereby limiting transmission cycles.

Disaster Medicine

A discipline resulting from the integration of emergency medicine and disaster management, focused on providing maximum care to the greatest number of victims based on resources and survival likelihood.

Endemic

The typical, baseline, or expected incidence and geographic occurrence of a disease within a specific population or region.

Epidemic (Outbreak)

The occurrence of cases of an illness, health-related behavior, or event in a community or region clearly in excess of normal expectancy for a given place and time.

Case Definition

A standard set of uniform criteria incorporating clinical symptoms, laboratory test results, and temporal/spatial boundaries to classify whether an individual has a specific disease condition.

Attack Rate (Affected Proportion)

A cumulative incidence measure used in outbreaks calculated as the number of affected animals or individuals divided by the total population at risk during the event.

Point-Source Epidemic

An outbreak stemming from a common, simultaneous exposure of a group to an agent, characterized by a rapid, steep single peak in the epidemic curve occurring within one incubation period.

Propagated Epidemic

An outbreak characterized by person-to-person or animal-to-animal transmission cycles, resulting in an epidemic curve with multiple successive waves or peaks over time.

Spot Map

A geographic visualization plotting individual case locations to detect disease clustering and spatial distribution patterns without accounting for denominator population sizes.

Line List

An organizational outbreak tool where each case is recorded as a single row containing standardized columns for clinical signs, onset dates, demographic data, and laboratory results.

Saiga Antelope Mass Die-Off (2017)

An acute mass mortality event in Kazakhstan where nearly $200{,}000$ antelopes died over a $3$-week period from hemorrhagic septicemia (Pasteurella multocida type B), triggered by high ambient humidity and temperature.

Foreign Animal Disease Diagnostician (FADD)

A specially trained veterinary officer dispatched during the initial 48 hours of suspected foreign animal disease detection to conduct field epidemiological investigations, collect duplicate diagnostic samples, and implement quarantine measures.

Rift Valley Fever Virus (RVFV)

A mosquito-borne phlebovirus (Phenuiviridae) endemic in Africa and the Arabian Peninsula that causes severe abortion storms (near $90\%$ fetal loss) in ruminant livestock and acute zoonotic disease in humans.

DDvax

A candidate human vaccine developed against Rift Valley fever virus evaluated in a Phase I clinical trial at the Bagamoyo Clinical Trial Facility of the Ifakara Health Institute in Tanzania.