Severe acute respiratory syndrome coronavirus (SARS-CoV) is a viral infection caused by a coronavirus that results in a flu-like respiratory illness. There was an outbreak of SARS-CoV in 2002 that led to a pandemic in 2003, but the virus was quickly contained.
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Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a novel coronavirus first identified in Wuhan, China, in December 2019. It became a pandemic throughout 2020 and into 2021. Infection with SARS-CoV-2 leads to a potentially severe respiratory illness called COVID-19.
What is coronavirus?
A coronavirus is a common virus from a large family of viruses that can cause illnesses such as the common cold and SARS. Not all coronaviruses are dangerous, but some can be fatal.
Coronaviruses can be spread in a mutated form from animals to humans. The 2002 SARS-CoV pandemic first passed from civet cats to humans. The exact origin of SARS-CoV-2 has not yet been identified, but most scientists believe it originated in bats and may have mutated through intermediate species, possibly pangolins.
What is SARS-CoV?
SARS-CoV is a viral respiratory illness that was first reported in China in 2002 and identified in February 2003. It caused an outbreak of severe acute respiratory syndrome (SARS) in Asia, and led to cases in North America, South America and Europe around the world.
SARS-CoV did pose a high fatality risk, but the outbreak lasted a short period, ending in June 2003. There were 8,098 cases reported globally, and 774 deaths, with a case fatality rate of 9.6 percent.
SARS-CoV was believed to have been initially transmitted from small mammals in a mutated form to humans.
What is SARS-CoV-2?
The outbreak of SARS-CoV-2 began in December 2019, and by March 15, 2021, the global case rate had reached 120 million and deaths had reached 2.65 million. The initial global spread was heightened through infection on a cruise ship in Japan, a religious mass gathering in South Korea, and in skiing resorts in Italy and Austria. As a result, epidemics occurred in many countries.
Symptoms
SARS-CoV
Symptoms of a SARS-CoV infection are:
- Fever
- Fatigue
- Muscle pain
- Headache
- Loss of appetite
- Diarrhea
- Shivering
In the later stages of the infection, a person can experience a dry cough, breathing difficulties, and low levels of oxygen in the blood, which can be fatal.
SARS-CoV-2
SARS-CoV-2 causes mild symptoms in most cases, and can many people are asymptomatic. The possible symptoms of a SARS-CoV-2 infection are:
- High temperature
- A continuous, dry cough
- Loss of the sense of taste and smell.
SARS-CoV-2 is less likely to be fatal than SARS-CoV. However, SARS-CoV-2 is more easily spread.
Transmission and R0
SARS-CoV
SARS-CoV is an airborne virus and is spread through small droplets of saliva that are released into the air through coughs and sneezes. When another person breathes in these droplets, an infection can occur.
SARS-CoV can also be transmitted via fomites (an object or surface infected with the virus) such as door handles. The virus can also be transmitted through feces if a person does not wash their hands after going to the toilet.
SARS-CoV was a nosocomial infection, meaning it was mainly transmitted in healthcare facilities. Transmission mainly occurred during the second week of infection.
At the beginning of the outbreak in 2002, the R0 value was estimated to be between 2·0 and 3·0.
A 2020 study comparing SARS-CoV and SARS-CoV-2 stated that the viral load is higher and lasts longer in the lower respiratory tract in people that experience severe COVID-19 illness. In SARS-CoV, upper respiratory tract infections did not occur with lower respiratory tract infections, meaning the transmission of SARS-CoV was lower than SARS-CoV-2 in the first 5 days of infection.
A comparison of the transmissibility and severity of illness caused by the two viruses is below.
| |
SARS-CoV
|
SARS-CoV-2
|
|
Transmissibility R0
|
~2·4
|
~2·5
|
|
Incubation period
|
2 to 7 days
|
1 to 14 days
|
|
Number of patients with mild illness
|
Low
|
High
|
|
Number of patients needing hospitalization
|
Most patients (over 70 percent)
|
Few patients (20 percent)
|
|
Risk factors for severe illness
|
Increased age, underlying illnesses
|
Increased age, underlying illnesses
|
SARS-CoV-2
SARS-CoV-2 has an approximate R0 value of 2·5. For R0 to reach less than 1, the transmission rate has to be reduced by over 60 percent.
SARS-CoV-2 can be spread through droplets released by coughing and sneezing that are then breathed in by another person.
When comparing the aerosol and surface transmissibility of SARS-CoV and SARS-CoV-2, researchers found that SARS-CoV-2 was detected for up to 72 hours after it was applied to plastic, stainless steel, copper, and cardboard. The differences in the viability of these two viruses found in this study, and the reduction in the amount of infectious virus on each surface, are detailed below.
|
Environment
|
SARS-CoV
|
SARS-CoV-2
|
|
Aerosol
|
Viable for 3 hour experiment time
Infectious titer reduced from 104.3 to 103.5 TCID50 per milliliter.
|
Viable for 3 hour experiment time
Infectious titer reduced from 105 to 102.7 TCID50 per liter of air
|
|
Cardboard
|
No viable virus found after 8 hours
|
Viable virus found after 72 hours
|
|
Copper
|
No viable virus found after 8 hours
|
No viable virus found after 4 hours
|
|
Plastic
|
Viable for 6.8 hours
|
Viable for 6.8 hours
|
|
Stainless steel
|
Viable for 5.6 hours
Infectious titer reduced from 103.7 to 100.6 TCID50 per milliliter after 72 hours
|
Viable for 5.6 hours
Infectious titer reduced from 103.7 to 100.6 TCID50 per milliliter after 48 hours
|
This study suggests that the stability of the two viruses on surfaces and aerosols is similar. It also suggests that differences in the transmissibility of these viruses may result from other factors such as higher viral loads in the upper respiratory tract in SARS-CoV-2 than in SARS-CoV.
Studies have suggested that SARS-CoV was less able to survive in warmer temperatures, with its infectious titer reducing at 38C and 95% humidity. At 4°C, SARS-CoV was able to survive for 28 days. There is currently no definitive data on the effect of temperature on SARS-CoV-2, but the insight into SARS-CoV suggests it may be less able to survive in warmer temperatures.
Treatment
SARS-CoV
There is no vaccine for SARS-CoV and any treatment is supportive. This means the body is supported while it fights the virus naturally, with ventilators to assist breathing, antibiotics to kill bacteria that cause pneumonia, or steroids to reduce inflammation in the lungs.
SARS-CoV-2
Treatment for SARS-CoV-2 is also supportive. The body is supported while it fights the virus naturally, with ventilators to assist breathing and maintain good oxygen levels in the blood. Many drugs have been tested out as therapeutic measures, and different ones are being used in different parts of the world.
Many vaccines have now been developed and are being rolled out across the globe.
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Genomic comparison
SARS-CoV-2 is genetically similar to SARS-CoV. SARS-CoV is the nearest human coronavirus relative of SARS-CoV-2 with an 86.85% similarity, which is reflected in their similar names. The currently known closest relative of SARS-CoV-2 is the bat coronavirus RaTG13 which has 96.75% similarity.
This suggests all three viruses have a similar ancestor, but SARS CoV-2 and RaTG13 have a more recent shared ancestor. Whilst the exact origin of SARS-CoV-2 is not yet known, most researchers think it originated from a bat coronavirus and some suspect that an intermediate species hosted the virus, possibly a pangolin due to similarities between the SARS-CoV-2 spike protein and those found in pangolin coronaviruses.
Summary
While SARS-CoV is no longer a pandemic threat, SARS-CoV-2 is a current and evolving pandemic. SARS-CoV-2 has a high amount of people with mild or no symptoms, meaning that detecting and tracking the transmission and then controlling the virus is harder than with SARS-CoV.
Those most at risk of severe illness from SARS-CoV and SARS-CoV-2 are older people and those with underlying health conditions. Treatments are similar for both SARS-CoV and SARS-CoV-2, but there are now vaccines for SARS-CoV-2.
References
Further Reading
One in four healthy young Marines report long-term physical, cognitive, or psychiatric effects after mild COVID-19