This article was updated on June 17, 2020

Coronaviruses typically affect the respiratory tracts of birds and mammals, including humans. Doctors associate them with the common cold, bronchitis, pneumonia, severe acute respiratory syndrome (SARS), and coronavirus disease 2019 (COVID-19). These viruses can also affect the gut.

Coronaviruses usually cause the common cold, though they can be responsible for more severe illnesses.

Over the past 80 years, scientists have found that these viruses can infect mice, rats, dogs, cats, turkeys, horses, pigs, and cattle. Sometimes, these animals transmit the viruses to humans.

Most recently, authorities identified a new coronavirus outbreak in China that has now reached other countries. The virus is called severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and it can cause COVID-19.

In this article, we explain the different types of human coronavirus, their symptoms, and how people transmit them. We also focus on three particularly dangerous diseases caused by coronaviruses: COVID-19, SARS, and Middle East respiratory syndrome (MERS).

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Covering the mouth when sneezing can help stop the spread of coronaviruses.

Researchers first identified a coronavirus in 1937, isolating one that was responsible for a type of bronchitis in birds that had the potential to devastate poultry stocks.

Scientists found evidence of human coronaviruses in the 1960s, in the noses of people with the common cold.

Human coronaviruses that are particularly prevalent include 229E, NL63, OC43, and HKU1.

The name “coronavirus” comes from the crown-like projections on their surfaces. “Corona” in Latin means “halo” or “crown.”

Among humans, coronavirus infections most often occur during the winter months and early spring.

In 2019, the Centers for Disease Control and Prevention (CDC) started monitoring the outbreak of a new coronavirus, SARS-CoV-2, which causes COVID-19. Authorities first identified the virus in Wuhan, China.

Since then, the virus has spread to nearly every country, leading the World Health Organization (WHO) to declare a pandemic.

The new coronavirus has been responsible for millions of infections globally, causing hundreds of thousands of deaths. The United States has seen the highest number of these deaths.

The first people with COVID-19 had links to an animal and seafood market. This suggests that animals initially transmitted the virus to humans. Then, people with no connections to the market developed the disease, confirming that humans can pass the virus to each other.

Most people who get COVID-19 will have a mild form of the disease. According to the WHO, around 80% of people who get COVID-19 will recover without needing hospitalization.

The remaining 20% become seriously ill and develop difficulty breathing.

Some groups are more at risk of severe disease, including older adults and people with underlying medical concerns, including high blood pressure, heart and lung problems, diabetes, and cancer.

The mortality rate varies between countries. In the U.S., the death rate is around 6%.

According to the CDC, children are not at higher risk of COVID-19 than adults.

Pregnant women appear to have the same risk of COVID-19 as other adults. However, during pregnancy, women have a higher risk of severe illness from viruses that are similar to SARS-CoV-2 and influenza.

The CDC also recommend that infants born to women with suspected or confirmed COVID-19 are put into isolation.

Symptoms of COVID-19

According to the CDC, people may start to experience symptoms 2–14 days after exposure to the virus. Symptoms may include:

  • a fever
  • chills
  • a cough
  • shortness of breath or difficulty breathing
  • sore throat
  • congestion or a runny nose
  • fatigue
  • headache
  • muscle pain
  • new loss of taste or smell
  • nausea or vomiting
  • diarrhea

No vaccine is currently available for COVID-19. However, scientists have now replicated the virus. This could allow for early detection and treatment in people who have the virus but are not experiencing symptoms.

According to the CDC, the following groups have a higher risk of developing serious illness from COVID-19:

  • people aged 65 years or older
  • people living in nursing homes or care facilities
  • people of any age who have serious underlying medical conditions, including chronic lung disease, serious heart conditions, severe obesity, a compromised immune system, or diabetes

The CDC note that although there have been reports of complications in young children, these are rare. COVID-19 most commonly produces mild symptoms in children.

Cold- or flu-like symptoms usually set in around 2–4 days after the infection develops. Typically, the symptoms are mild, though they vary from person to person. In some people, coronavirus infections are fatal.

Symptoms may include:

  • a runny nose
  • a headache
  • a cough
  • a fever
  • a sore throat
  • generally feeling unwell

While scientists can easily cultivate rhinoviruses — which also cause the common cold — in the laboratory, this is not the case with coronaviruses. This makes it difficult to gauge the impact of these pathogens.

There is currently no cure for the cold-like illnesses caused by coronaviruses. Treatments include self-care and over-the-counter medications.

Taking the following steps may help:

  • resting and avoiding overexertion
  • drinking plenty of water
  • avoiding smoking and smoky areas
  • taking acetaminophen (Tylenol) to reduce pain and a fever
  • using a clean humidifier or cool mist vaporizer

A doctor can identify the virus responsible in a sample of fluid from a person’s body, such as a sample of blood or mucus from the nose.

Coronaviruses belong to the subfamily Coronavirinae in the family Coronaviridae.

Different types of coronavirus vary, in terms of the severity of disease that they cause and how far they spread.

Doctors currently recognize seven types of coronavirus that can infect humans.

Common types include:

  • 229E (alpha coronavirus)
  • NL63 (alpha coronavirus)
  • OC43 (beta coronavirus)
  • HKU1 (beta coronavirus)

Rarer strains that cause more severe illnesses include MERS-CoV, which causes the disease MERS, and SARS-CoV, the virus responsible for SARS.

In 2019, a new strain, called SARS-CoV-2, started circulating, causing the disease COVID-19.

The CDC recommend that all people wear cloth face masks in public places where it is difficult to maintain a 6-foot (2-meter) distance from others. This will help slow the spread of the virus from asymptomatic people and people who do not know that they have contracted it. People should wear cloth face masks while continuing to practice physical distancing. Instructions for making masks at home are available here. Note: It is critical that surgical masks and N95 respirators are reserved for healthcare workers.

Researchers believe that the viruses transmit via fluids in the respiratory system, such as mucus.

For example, a coronavirus can spread when a person:

  • coughs or sneezes without covering their mouth, dispersing droplets into the air
  • touches someone who has the infection
  • touches a surface that has the virus, then touches their own nose, eyes, or mouth

Some animal coronaviruses may spread to humans through contact with feces, though it is unclear whether human coronaviruses can spread in the same way.

Coronaviruses will infect most people at some point.

To prevent transmission, people with symptoms should stay at home, rest, and avoid coming into close contact with other people.

Covering the mouth and nose with a tissue or handkerchief while coughing or sneezing can also help prevent transmission. It is important to dispose of used tissues right away and maintain proper hygiene around the home.

SARS is a contagious disease that develops from infection with the SARS-CoV coronavirus. In many cases, it leads to a life threatening form of pneumonia.

In November 2002, the virus started circulating in the Guangdong province of southern China, eventually reaching Hong Kong. From there, it rapidly spread, causing infections in more than 24 countries.

Experts no longer consider SARS a risk. Since 2003, there have only been a few cases due to laboratory accidents or, possibly, transmission from animals.

SARS-CoV affects both the upper and lower respiratory tract.

The symptoms of SARS develop over 1 week and start with a fever. Early on, people develop flu-like symptoms, such as:

  • a dry cough
  • chills
  • diarrhea
  • breathlessness
  • aches

Pneumonia, a severe lung infection, usually develops. At its most advanced stage, SARS causes failure of the lungs, heart, or liver.

According to the CDC, authorities reported that 8,098 people contracted SARS during the outbreak. Among these people, 774 died of the disease. This indicates a mortality rate of 9.6%.

Complications are more common among older adults. According to one source, more than half of those who died from the infection were over the age of 65. Authorities eventually controlled SARS in July 2003.

MERS is caused by the MERS-CoV coronavirus. Scientists first recognized this severe respiratory illness in 2012 after it surfaced in Saudi Arabia. Since then, it has spread to other countries.

The virus has reached the U.S. However, only two people in the country have tested positive for MERS-CoV, and this was in 2014. As a result, the CDC state that the risk of developing MERS in the U.S. is very low.

Symptoms of MERS include a fever, breathlessness, and coughing.

The illness spreads through close contact with people who have the infection.

A 2019 investigation into MERS found that the disease is fatal in 35.2% of people who develop it.

Keep up to date on the current COVID-19 outbreak. The CDC have also a resource on reducing the risk of infection.

Read the article in Spanish.