Global Health Vocabulary in English

An endemic disease is one that occurs consistently in a particular region or population at a predictable, stable level — for example, malaria in parts of sub-Saharan Africa. An epidemic is a sudden and significant increase in cases of a disease within a specific community or geographical area, beyond what is normally expected. A pandemic is an epidemic that has spread across multiple countries or continents, affecting a large number of people internationally.

Morbidity refers to the presence of illness, disease, or disability in a population — it describes how many people are affected by a condition, not how many have died from it. Mortality refers to the occurrence of death, typically expressed as a rate per population. For example, a disease may have high morbidity (many people become ill) but low mortality (few die from it), as is the case with the common cold.

Incidence refers to the number or rate of new cases of a disease that arise in a population during a specific time period. Prevalence refers to the total number or proportion of people in a population who have the disease at a given point in time, including both new and existing cases. Incidence tells you how fast a disease is spreading; prevalence tells you how widespread it currently is.

Herd immunity occurs when a sufficient proportion of a population has become immune to a disease — either through vaccination or previous infection — that the pathogen can no longer spread efficiently. This protects even those who cannot be vaccinated, such as newborns or immunocompromised individuals. The threshold required for herd immunity varies by disease: measles requires around 95% immunity, while it is lower for less contagious diseases.

Quarantine applies to people who have been exposed to a disease but have not yet shown symptoms. It separates them from others to prevent potential spread during the incubation period. Isolation applies to people who are already confirmed ill, separating them from those who are healthy to prevent transmission. During the COVID-19 pandemic, both terms were widely used but sometimes confused in public communications.

In global health, surveillance refers to the continuous, systematic collection, analysis, and interpretation of health data to inform public health action. Disease surveillance systems track the occurrence and spread of illnesses, identify outbreaks early, and monitor the effectiveness of interventions. International surveillance networks, coordinated by bodies such as the WHO, enable countries to share data and respond collectively to emerging health threats.

Vector-borne diseases are illnesses caused by parasites, bacteria, or viruses transmitted through the bite of an infected arthropod or other carrier (the vector). Common vectors include mosquitoes, ticks, and sandflies. Examples of vector-borne diseases include malaria (Anopheles mosquito), dengue fever (Aedes mosquito), Lyme disease (ticks), and leishmaniasis (sandflies). Climate change is expanding the geographical range of many vectors, posing new public health challenges.

The case fatality rate (CFR) is the proportion of people who have been diagnosed with a disease who die from it within a defined period. It is calculated by dividing the number of deaths by the total number of confirmed cases and expressing it as a percentage. The CFR is an important measure of a disease’s severity, though it can be affected by testing rates: if only severe cases are tested, the CFR will appear higher than it truly is.

Sanitation — the provision of facilities and services for safe disposal of human waste and the maintenance of clean water supplies — is one of the most important determinants of public health. Poor sanitation is a leading cause of waterborne diseases such as cholera, typhoid, and dysentery, which kill hundreds of thousands of people each year. Improving access to clean water and sanitation is a central goal of the UN Sustainable Development Goals (SDGs) and is directly linked to reductions in child mortality and malnutrition.

Global health vocabulary is essential for healthcare professionals, public health students, researchers, journalists, and policy analysts working in international settings. The primary language of the WHO, leading medical journals, international health conferences, and global health research is English. Understanding terms like epidemiology, containment, and intervention enables professionals to access, produce, and critically evaluate the research and guidance that shapes health outcomes worldwide.