coronavirus
What is a coronavirus?
How do I protect myself from the coronavirus?
Does the virus that causes COVID-19 belong to the coronavirus family?
What are common types of coronaviruses?
coronavirus, a group of viruses known for their ability to cause respiratory and gastrointestinal infections in humans and animals, including poultry and cattle. They belong to the family Coronaviridae and are characterized by enveloped virions (virus particles) that are about 120 nm (1 nm = 10−9 meter) in diameter. Distinctive club-shaped glycoprotein spikes project from their surface, giving them a crownlike, or coronal, appearance under a microscope—hence, the name coronavirus.
In humans, coronaviruses are best known for causing respiratory illnesses, which can range from the common cold to severe diseases such as COVID-19. Some strains can also infect the digestive tract. In animals, coronaviruses commonly cause intestinal infections, leading to symptoms such as diarrhea, dehydration, and reduced growth, particularly in young livestock and birds.
Structure
Coronaviruses have a complex structure that supports their ability to infect host cells. They are surrounded by a lipid envelope derived from the host cell, which makes them vulnerable to substances such as soap and alcohol. Embedded in this envelope are the spike (S) proteins, which enable the virus to bind to host cell receptors, as well as membrane (M) and envelope (E) proteins, which help maintain structure and assist in viral assembly. Inside, the virus contains a helical or tubular nucleocapsid, where the single-stranded positive-sense RNA genome is bound to nucleocapsid (N) proteins. This relatively large RNA genome allows coronaviruses to efficiently direct host cells to produce new viral particles.
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Types
The virus family Coronaviridae is divided into multiple groups, with the principal subfamily, Orthocoronavirinae, including four major genera: Alphacoronavirus, Betacoronavirus, Gammacoronavirus, and Deltacoronavirus. Members of these groups are known to infect a range of hosts, particularly mammals and birds.
SARS-CoV-1
In humans, a species known as SARS-CoV-1 (or severe acute respiratory syndrome coronavirus), a member of Betacoronavirus, causes a highly contagious respiratory disease. The illness is characterized by symptoms of fever, cough, and muscle ache, often with progressive difficulty in breathing. The virus emerged in humans in 2002 and is thought to have originated from an animal source, most likely horseshoe bats. Its emergence in humans was made possible by genetic changes that enabled the virus to infect human cells and spread between individuals.
MERS-CoV
In 2012 another coronavirus capable of causing a severe acute respiratory illness later known as Middle East respiratory syndrome (MERS) was discovered in humans. The MERS virus, known as MERS-CoV, is another type of Betacoronavirus. MERS was first identified in Saudi Arabia, with additional cases reported within the following year in countries including France, Germany, Jordan, Qatar, Tunisia, the United Arab Emirates, and the United Kingdom. All confirmed infections were directly or indirectly associated with the Middle East. Since its emergence, approximately one-third of reported cases have resulted in death. The MERS coronavirus shares similarities with other coronaviruses suspected to have originated in bats and is thought to have spread from bats to intermediate hosts before infecting humans. Dromedary camels are a key reservoir, playing a significant role in transmission to humans.
SARS-CoV-2
In late 2019 a virus closely related to SARS-CoV-1 emerged in Wuhan, China. The virus, later named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), causes the disease COVID-19, which primarily affects the respiratory system and often presents with symptoms such as fever and cough. The virus spread rapidly, reaching multiple regions—including Asia, Europe, and North America—by early 2020 through international travel. In March 2020 the World Health Organization declared the outbreak a pandemic, and travel to, from, and within many countries was severely restricted in an effort to control its spread. In many areas, schools and numerous businesses closed, and stay-at-home guidelines were implemented, which strongly encouraged people not to leave their place of residence. By the end of 2020, vaccines had been developed and distributed, enabling a gradual return to normal activities in many parts of the world.
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Over the course of the COVID-19 pandemic, multiple variants of SARS-CoV-2 emerged, each with differing characteristics. In mid-2021, the Delta variant became widespread and was notably more transmissible than earlier forms of the virus, leading to increased infections, including some among vaccinated individuals, and causing significant illness, particularly in those who were unvaccinated. Later, in late 2021, the Omicron variant rapidly became the dominant strain in many regions, including the United Kingdom and the United States. Although Omicron spread more easily than Delta, it generally caused milder symptoms in most people; however, it still resulted in substantial numbers of hospitalizations, especially among individuals who were not vaccinated.
Other coronaviruses
HCoV-OC43 and HCoV-HKU1, along with HCoV-229E and HCoV-NL63, are common human coronaviruses that typically cause mild respiratory illnesses. They are among the viruses responsible for the common cold, producing symptoms such as cough, sore throat, runny nose, and fever. Although infections are usually mild, they can occasionally lead to more serious complications, particularly in young children, older adults, or individuals with weakened immune systems.