What is the difference between pandemic, endemic, and epidemic?

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An endemic disease is one that is always present throughout a specific region or population. The prevalence of the disease remains fairly stable and predictable over time.

Examples

Some examples of endemic conditions include:

• Malaria: This mosquito-borne illness is present in many countries worldwide. However, it is endemic to parts of Africa, among other places, because the higher temperatures allow the Anopheles mosquito, which spreads malaria, to thrive. This means that malaria remains at constant levels in this region.
• Coccidioidomycosis: Inhaling fungal spores causes this condition, which is also known as valley fever. It is endemic to the Southwestern U.S. and northern Mexico.
• Dengue fever: This condition is endemic to tropical and subtropical regions because, as with malaria, it spreads through mosquito bites. The Aedes mosquito carries viruses that can cause dengue fever.
• Hepatitis B: The hepatitis B virus (HBV) is endemic worldwide, although it has higher endemicity in Africa and Asia than in Europe and North America. HBV spreads through contact with blood that contains the virus. Due to this, it does not cause the sudden outbreaks that airborne viruses can.

An epidemic occurs when a disease spreads unexpectedly or quickly across a geographical area or population. It can occur if an endemic disease suddenly becomes more prevalent, or if a new disease begins to affect a region or group.

Many examples of epidemics involve contagious illnesses, but there are exceptions.

Examples

Some examples of epidemics include:

• Zika virus: Scientists first identified this mosquito-borne virus in monkeys in 1947. Zika virus began affecting humans in the 1950s, but it did not cause its first outbreak until 2007. In 2014, it caused an outbreak in Polynesia and then Brazil. From here, it quickly spread to the Caribbean and most of South America.
• Ebola virus: There have been several outbreaks of ebola in various African nations since the 1970s, but in 2013, it became an epidemic in West Africa.
• Opioids: In the U.S., the use of opioids has increased dramatically in recent decades, causing a substantial increase in overdoses. Between 1999 and 2019, there were nearly 500,000 deaths due to opioid overdose. Many more people have ongoing addictions to these substances, which include prescription medication and recreational drugs, such as heroin.

A pandemic occurs when a disease spreads across countries or continents. Scientists may determine that a disease has become a pandemic if it spreads at a very fast rate, with new cases appearing every day.

Pandemics have become more likely due to international travel. People travel to different countries and continents more often than before. Greater urbanization also means that many people live in densely populated towns and cities. This proximity allows the rapid transmission of pathogens from person to person.

Changes in how people use land and exploit the natural environment also play a role. Several pandemics from the past few decades have been zoonotic diseases, which means that they result from viruses that originally affected a species of animal.

However, close contact between animals and humans increases the likelihood of such viruses evolving and adapting to infect humans, too. Some examples of activities that increase the chance of this include:

• keeping livestock
• hunting or trading wild animals
• eating wild animals

Examples

Some examples of pandemics include:

• Bubonic plague: The bubonic plague, also known as the “Black Death,” spreads through flea bites. A bacterium known as Yersinia pestis causes it. The bubonic plague became a pandemic in the 14th century. The disease still exists today and is most endemic in Madagascar, the Democratic Republic of the Congo, and Peru. It is also present in the U.S., particularly in the southwestern states, which include Arizona and Colorado.
• 1918 influenza: A specific strain of influenza (flu) virus caused this pandemic. It affected more than one-third of the global population in 1918 and caused about 50 million deaths.
• HIV: This virus attacks the immune system, making people vulnerable to many other infections. Experts believe that HIV came from chimpanzees before transmitting to humans. This transmission may have happened as early as the late 19th century. HIV reached the United States in the mid-to-late 1970s.
• Severe acute respiratory syndrome (SARS): A virus known as SARS-CoV-1 causes this disease. Experts first identified the virus in Asia in 2003. SARS spread to more than 24 countries in various continents before international efforts to contain it proved successful.
• Swine flu: The H1N1 virus causes swine flu. The first known cases of swine flu in the U.S. were in 2009. The virus, which contains a unique combination of influenza genes that scientists had never seen before, spread across the globe, causing an estimated 151,700–575,400 fatalities worldwide.
• COVID-19: The SARS-CoV-2 virus causes this disease, which experts first detected in late 2019. Many scientists believe that it originated in a wild animal before transmitting to humans, although the exact origin is unclear.

The terms “pandemic,” “epidemic,” and “endemic” do not describe the severity of a disease. Instead, they describe its prevalence. This means that one is not inherently worse than the other.

For example, it is possible for an endemic illness to devastate communities and economies. The term indicates that the level of disease remains steady, rather than the number of cases.

It is also possible to have mild pandemics, in which an illness travels rapidly to many regions but does not cause severe illness or death. In contrast, an epidemic could be severe, causing significant illness and death in most of the people whom it affects.

What someone considers to be the worst depends on what they are measuring. In terms of scale, pandemics are the largest and have the biggest potential to cause worldwide disruption. Whether they fulfill this potential depends on the disease and how humans respond to it.

An endemic disease can become an epidemic or pandemic, and vice versa.

An example of this is cholera. This illness occurs when a person swallows water or food containing Vibrio cholerae bacteria. It originated in India, but in the 19th century, it caused an outbreak that ultimately spread across the globe.

This cholera pandemic was the first of seven. The seventh, which still affects South Asia, Africa, and the Americas, is ongoing.

However, in many places, cholera has become endemic. This means that it is constantly present at relatively steady levels. Epidemics can also occur, even in locations without endemic cholera.

An endemic disease is not necessarily inevitable, and action may still be necessary to stop it. Cholera, for example, is a treatable and preventable disease. Clean water, sanitation, rehydration treatment, and vaccines can easily prevent many of the deaths that cholera currently causes.

Endemic, epidemic, and pandemic are all terms that scientists use to categorize diseases in terms of how widespread they are.

An endemic condition is one that is constant among a population or area, while an epidemic is a sudden spike in cases in one population or location. A pandemic is similar, but it spreads farther, affecting multiple regions or continents.

The severity of a disease depends on several factors. Due to this, although a pandemic affects a higher number of people, it is not necessarily more lethal than an epidemic or an endemic disease.