Coronaviruses are a large family of viruses that cause respiratory illness ranging in severity from the common cold to fatal pneumonia.
There are many different coronaviruses. Most of them cause illness in animals.
Four human coronavirus infections involve mild upper respiratory tract illness that causes symptoms of the common cold.
However, 3 human coronavirus infections can be much more severe and have recently caused major outbreaks of deadly pneumonia:
SARS-CoV-2 is a novel coronavirus that was first identified in late 2019 as the cause of coronavirus disease 2019 (COVID-19). This infection is discussed elsewhere (see COVID-19).
MERS-CoV was identified in 2012 as the cause of Middle East respiratory syndrome (MERS).
SARS-CoV-1 was identified in 2003 as the cause of an outbreak of severe acute respiratory syndrome (SARS) that began in China near the end of 2002.
These coronaviruses that cause severe respiratory infections are transmitted from animals to humans (zoonotic pathogens).
Middle East Respiratory Syndrome (MERS)
The virus that causes Middle East respiratory syndrome (MERS) is a coronavirus.
The MERS virus was first detected in Jordan and Saudi Arabia in 2012. As of 2021, worldwide, there were over 2,500 confirmed cases of MERS, with over 900 related deaths. Most occurred in Saudi Arabia, where new cases continue to appear. The largest known outbreak of MERS outside the Arabian Peninsula occurred in the Republic of Korea in 2015. The outbreak was associated with a traveler returning from the Arabian Peninsula. Cases have also occurred in countries throughout Europe, Asia, North Africa, the Middle East, and the United States in people who were either transferred there for care or became ill after returning from the Middle East. Only a handful of cases have been reported since 2019.
In several countries in the Middle East, dromedary camels are suspected of being the primary source of infection for people, but how the virus spreads from camels to people is unknown.
The infection is more common among men and is more severe in older adults and in people with an underlying chronic disorder such as diabetes or a heart or kidney disorder. The infection has been fatal in about one third of infected people.
The MERS virus is spread through close contact with people who have MERS or through airborne droplets that were coughed or sneezed out by an infected person. People are not thought to be contagious until symptoms develop. Most cases of person-to-person spread have occurred in health care workers caring for infected people.
Symptoms usually appear about 5 days (but anywhere from 2 to 14 days) after people are infected. Most people have a fever, chills, muscle aches, and cough. About one third have diarrhea, vomiting, and abdominal pain.
Diagnosis of MERS
Testing of fluids from the respiratory tract
Blood tests
Doctors suspect MERS in people who have a lower respiratory tract infection and have traveled to or reside in an area where they could have been exposed to the virus or who have had recent close contact with someone who may have had MERS.
To diagnose MERS, doctors take a sample of fluids from several places in the respiratory tract at different times and test it for the virus. They also do blood tests to detect the virus or antibodies to it. Blood tests are done on all people who have had close contact with someone who may have MERS.
Treatment of MERS
Medications to relieve fever and muscle aches
Isolation
Precautions are taken to prevent the spread of the virus. For example, the person is isolated in a room with a ventilation system that limits the spread of microorganisms in the air. People who go into the room must wear a special mask, eye protection, and a gown, cap, and gloves. Doors to the room should be kept closed except when people enter or leave the room, and people should enter and leave as few times as possible.
Severe Acute Respiratory Syndrome (SARS)
No cases had been reported worldwide since 2004.
Symptoms of SARS resemble those of other more common respiratory viral infections (such as fever, headache, chills, and muscle aches) but are more severe, especially among older adults.
Doctors suspect SARS only if people may have been exposed to an infected person.
If doctors think a person may have SARS, the person is isolated in a room with a ventilation system that limits the spread of microorganisms in the air.
(See also Overview of Viral Infections.)
Severe acute respiratory syndrome (SARS) was first detected in China in late 2002. A worldwide outbreak occurred, resulting in more than 8,000 cases worldwide, including Canada and the United States, and about 800 deaths by mid 2003. No cases had been reported worldwide since 2004.
Although no new cases have been reported since 2004, SARS is not considered eliminated because the virus has an animal reservoir from which it conceivably could reemerge.
The immediate source was presumed to be civets, cat-like mammals, that were being sold in live animal markets as exotic food. How civets became infected is unclear, though bats are thought to be the reservoir host of the SARS virus in nature.
SARS is caused by a coronavirus. SARS is much more severe than most other coronavirus infections, which usually cause only coldlike symptoms. However, the Middle East respiratory syndrome (MERS) and COVID-19 are other severe illnesses caused by a coronavirus.
SARS is spread from person to person through close contact with an infected person or through airborne droplets that were coughed or sneezed out by an infected person.
Symptoms of SARS
Symptoms of SARS resemble those of other more common respiratory viral infections but are more severe. They include fever, headache, chills, and muscle aches, followed by a dry cough and sometimes difficulty breathing.
Most people recovered within 1 to 2 weeks. However, some developed severe difficulty breathing, and about 10% died.
Diagnosis of SARS
A doctor's evaluation
Tests to identify the virus
SARS is suspected only if people who may have been exposed to an infected person have a fever plus a cough or difficulty breathing.
Tests can be done to identify the virus.
Treatment of SARS
Isolation
If needed, oxygen
Sometimes a ventilator to help with breathing
If doctors think a person may have SARS, the person is isolated in a room with a ventilation system that limits the spread of microorganisms in the air. In the first and only outbreak of SARS, such isolation kept the virus from being transmitted and eventually eliminated it.
People with mild symptoms need no specific treatment. Those with moderate difficulty breathing may need to be given oxygen. Those with severe difficulty breathing may need mechanical ventilation to aid breathing.
