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.
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.
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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.
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 i