While the world is firmly in the grip of the COVID-19 pandemic, we take a look back at SARS and MERS and their underlying pathogens, which are also coronaviruses.

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Three new coronaviruses have emerged since the turn of the century.

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Coronaviruses are a large family of enveloped RNA viruses that mostly infect birds and mammals.

In humans, they can cause mild infection in the upper respiratory tract, like the common cold, but also more serious lower respiratory tract infections.

These infections can manifest as bronchitis, pneumonia, or a severe respiratory illness, such as severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), or coronavirus disease 19 (COVID-19).

But how similar are the SARS, MERS, and COVID-19 coronaviruses? And how do the diseases compare?

In this feature, we explore the history of each coronavirus outbreak, as well as the statistics and medical advances.

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The coronavirus that causes SARS is called SARS-CoV. According to the World Health Organization (WHO), the first cluster of SARS cases occurred in China’s Guangdong province in November 2002.

Research has identified horseshoe bats as the natural reservoir of SARS-CoV. Civets and animals in wet markets also likely contributed to the virus crossing from animals into humans.

The organization was first notified, of more than 100 deaths due to a new infectious disease, on February 10, 2003. The next day, the Chinese health ministry made an official report of 300 cases and five deaths due to an acute respiratory syndrome.

On March 12, 2003, the WHO issued a global alert, warning of atypical pneumonia spreading among hospital staff.

A mere 3 days later, the WHO coined the name SARS and put out an emergency travel advisory, asking travelers to be familiar with the symptoms of the condition. They also proposed that the disease was spreading throughout the world by people using air transport.

Later in March, the WHO recommended that airports in areas with cases of SARS screen passengers.

From April of that year onward, the WHO issued a number of warnings, asking people to postpone all but essential travel to affected areas. These areas included, at various times, Hong Kong, Toronto, several areas of mainland China, and Taiwan.

A paper published May 15, 2003 in The New England Journal of Medicine identified a new coronavirus as the underlying pathogen.

The WHO officially declared the SARS epidemic to be contained on July 5 of that year. Since then, there have been four small outbreaks of SARS.

Of these, three involved people who worked with the SARS virus in laboratory settings and acquired the virus accidentally. The fourth incidence has been mostly attributed to infection from an animal source.

There have been no reported cases of SARS since then, although the WHO warn that “These events demonstrate that the resurgence of SARS leading to an outbreak remains a distinct possibility and does not allow for complacency.”

SARS summary:

  • Pathogen: SARS-CoV
  • Total number of cases: 8,439, 21% of which developed in healthcare workers
  • Number of cases in the United States: 73
  • Total number of deaths: 812
  • Case fatality rate: 9.6%
  • Mode of transmission: Droplets produced by coughing, sneezing, talking, or breathing
  • Mean incubation period: 5 days
  • Key symptoms: A cough (dry at first), a fever, and diarrhea in the first or second week of illness, or both
  • At risk groups: People with underlying medical conditions
  • Treatment: No specific treatment
  • Vaccine: No vaccine

MERS occurs as a result of infection with the coronavirus MERS-CoV.

On September 20, 2012, the Program for Monitoring Emerging Diseases reported a novel coronavirus isolated from sputum samples of a 60-year-old man from Saudi Arabia, who had died 3 months earlier.

Within the next month, the number of confirmed MERS cases rose to nine, with five fatalities. The earliest case dated back to April 2012.

Across the globe, 27 countries have reported cases of MERS since 2012, but around 80% of cases have occurred in Saudi Arabia.

MERS-CoV is a zoonotic virus, meaning that most cases of infection pass from animals to humans. According to the WHO, direct or indirect contact with dromedary camels is the most common route of infection.

Transmission among people is rare, and it mostly occurs among family members or in healthcare settings.

The MERS-CoV virus has similarities to European bat coronaviruses.

MERS summary:

  • Pathogen: MERS-CoV
  • Total number of cases: 2,519
  • Number of cases in the U.S.: 2
  • Total number of deaths: 866
  • Case fatality rate: 34.3%
  • Mode of transmission: Droplets from person to person, unclear from camels to humans
  • Key symptoms: A fever, a cough, shortness of breath
  • At risk groups: Men above the age of 60, particularly those with underlying medical conditions such as diabetes, high blood pressure, and kidney failure
  • Treatment: No specific treatment
  • Vaccine: No vaccine

The coronavirus SARS-CoV-2 is the pathogen that causes COVID-19. The virus has a close resemblance to SARS-CoV.

The first cases of COVID-19 were reported in Wuhan, China, in December 2019.

On January 5, 2020, the WHO published the first news of an outbreak of unknown cause. By the end of January, the organization had declared COVID-19 to be a public health emergency of international concern.

The name COVID-19 was officially coined, by the WHO, on February 11. Exactly 1 month later, the organization declared a pandemic.

To date, cases of COVID-19 have been reported on every continent except Antarctica. Governments across the world have responded with varying degrees of social distancing measures in a bid to curb the spread of the virus.

As the numbers of infections and deaths from COVID-19 continue to rise, researchers are working to identify suitable treatments and vaccines to curb the pandemic.

COVID-19 summary, as of April 9, 2020:

  • Pathogen: SARS-CoV-2
  • Total number of cases: 1,490,790
  • Number of cases in the U.S.: 432,438
  • Total number of deaths: 88,982
  • Case fatality rate: 1.38% to 3.4%
  • Mode of transmission: Droplets produced by coughing, sneezing, or talking, limited evidence of other routes
  • Mean incubation period: 5 days
  • Key symptoms: A fever, a dry cough, shortness of breath
  • At risk groups: Adults aged 65 and over, and people of all ages with underlying medical conditions
  • Treatment: No specific treatment, although several candidate drugs are undergoing testing
  • Vaccine: No vaccine, although several candidate vaccines are in development

Each of the three new coronaviruses that has emerged since the turn of the century has caused respiratory disease outbreaks, but each has also displayed unique features.

SARS and MERS have significantly higher case fatality rates than COVID-19. Yet COVID-19 is more infectious — the underlying SARS-CoV-2 virus spreads more easily among people, leading to greater case numbers.

Despite the lower case fatality rate, the overall number of deaths from COVID-19 far outweighs that from SARS or MERS.

There have been no cases of SARS for over a decade. But MERS is an ongoing public health concern.

One factor that could contribute to the extent of damage that any new coronavirus can cause is globalization. As infectious disease specialist and WHO advisor Prof. David Heymann told Medical News Today in an interview:

“In the past, coronaviruses that cause the common cold in humans also emerged, possibly in the same way as did the current pandemic.”

“But they did not have the opportunity to hop on international flights and spread rapidly around the globe,” he continued. “They likely circulated locally and then gradually spread to neighboring countries and onward throughout the world.”

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