Endemic infections

• ALSO KNOWN AS: Native diseases, regional diseases

Definition

Endemic infections are diseases that are constant, that vary in numbers and severity, and that are localized to a particular region or population. Endemic infections, or diseases, are caused by any of the pathogens that plague humans: bacteria, viruses, fungi, and parasites. Most endemic diseases are contagious, or communicable. Health conditions can also be described as endemic, and they include those conditions that lead to disease, such as obesity, poor maternal nutrition, and impure drinking water, within a particular area or community.

The World Health Organization’s list of some of the most common, and deadly, infectious diseases throughout the world includes many that are endemic, particularly in developing countries where sanitation is poor. This list of diseases includes cholera, a bacterial infection spread mostly through contaminated drinking water (endemic to Russia, sub-Saharan Africa, and the Indian subcontinent); Japanese encephalitis, a viral infection spread by mosquitoes that live in rice paddies (endemic to parts of rural East Asia); malaria, which is widespread in tropical and subtropical climates, but is endemic to sub-Saharan Africa, where 94 percent of the world’s cases of malaria occur; onchocerciasis, or river blindness (which is endemic to Africa), is caused by a parasitic worm that can live for years in the human body; and schistosomiasis, a parasitic infection that can damage the kidneys and is caused by a worm that swims freely in contaminated water (endemic to many developing countries).

Local Factors

The local climate and microclimate (humidity, temperature, access to safe water, sanitation, and the presence of potential animal or insect vectors) play a major role in certain diseases endemic to a specific region, especially diseases that are spread by indigenous insects. For example, Chagas’ disease, also known as American trypanosomiasis, causes many cases of heart disease in Central America and South America. The disease is caused by the protozoan parasite Trypanosoma cruzi, which is spread by the triatomine bug, or kissing bug (Triatoma pallidipennis), found in tropical regions. This insect carries the parasite in its feces. Humans who come into contact with the feces contract the parasite, which can cause chronic heart problems or death.

Some diseases, such as ear infections in children, are endemic to colder climates. Ear infections are not communicable. They develop when the eustachian tube (the air passage into the middle ear) becomes clogged and inflamed, usually as a secondary infection of the common cold, the endemic, ubiquitous scourge of cold climates. Other local factors that contribute to the balance of endemic infections in a given region include population density, a population's immunity, and access to healthcare.

Populations

The term endemic pertains to population groups, not individual persons. Therefore, chronic conditions are not endemic conditions. An endemic infection is entrenched and sustained within a population (but not necessarily exclusive to that population). For a contagious disease, such as chickenpox, to be sustained or endemic, each member of the population who becomes infected must transmit, or pass along, the infection to a minimum of one other person, on average, in the group. Members of these population groups share certain characteristics (such as age, gender, and genetic heritage) and are affected by the same external influences (such as poverty, social stressors, and climate) that make them susceptible to certain pathogens.

Classifications

Endemic, epidemic, and pandemic are the three broad categories used to describe the spread of infection. Because these categories are related, they are often confused. The common root “demic” comes from the Greek demos, meaning “people.”

Endemic infections. Endemic (en in Greek means “in”) infections are always present at various levels of dissemination in a region or population and remain so without outside inputs. For example, meningococcal diseases, most notably meningitis, are endemic to Canada. Because of their prevalence in the United States, human immunodeficiency virus (HIV) and hepatitis C are considered endemic. Worldwide, hepatitis B virus (HBV) is considered an endemic infection.

Epidemic infections. Epidemic (epi in Greek means “on” or “upon”) infections are sudden, severe outbreaks in a region or population. Many eventually become extinct. However, the number of infections and the aftermath of the outbreak can remain significant for a long time. For example, polio was an epidemic in the United States in the early 1950s, as well as West Africa's 2014 Ebola outbreak.

Pandemic infections. From the Greek word pan, meaning “all,” pandemic infections are epidemics that are geographically widespread across a region or even the entire planet. An example is the Spanish flu pandemic of 1918 and the COVID-19 pandemic of the early 2020s.

Endemic infections are further classified in a number of ways. One distinction is between holoendemic and hyperendemic diseases.

Holoendemic diseases are those diseases that affect almost all the inhabitants of a particular area but are more prevalent in children than in adults (and usually more severe) because of the acquired immunity. For example, over 90 percent of the world's malaria cases occur in Africa, and over 95 percent of malaria-related deaths occur on the continent. Within this population, children under five account for 76 percent of the deaths.

Hyperendemic diseases are those diseases that affect nearly everyone in a given population, but the prevalence is more or less equal across all age groups. The common cold during the cold season is an example of a hyperendemic disease.

A specific endemic infection can be quantified, or counted. One measure is prevalence, the number of cases of a certain disease in a specified region or population at a given time. The prevalence can be low or high, and it can vary, but the disease remains; it is always in the region or within the group.

Impact

The socioeconomic impact of endemic infections on various regions and human populations is impossible to calculate. One ongoing debate is whether to focus resources on control or eradication. The rise in globalization and global populations in the twenty-first century had an enormous effect on endemic infections.

Biological invasions are widespread. Travelers and transported goods carry insects and other living organisms worldwide. These invasions not only introduce new diseases but also increase the frequency and severity of local endemic diseases. Biologists have found that often, the introduced species serve as suitable hosts for local endemic disease agents (such as bacteria and parasites). The introduced hosts help maintain the endemic status of the disease, making that disease increasingly difficult for local health organizations to control or eradicate.

Bibliography

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