Severe Acute Respiratory Syndrome

Severe Acute Respiratory Syndrome (SARS) virus is a contagious and potentially fatal respiratory illness caused by the SARS-associated coronavirus (SARS-CoV). It emerged as a major global health concern in the early 21st century when an outbreak occurred in 2002–2003, originating from China and spreading to several countries. SARS marked one of the first significant coronavirus pandemics in modern history, setting the stage for later research into similar viruses such as MERS-CoV and SARS-CoV-2 (responsible for COVID-19).

Background and Origin

The SARS virus belongs to the Coronaviridae family and the Betacoronavirus genus, a group of enveloped, single-stranded RNA viruses known for their characteristic crown-like spikes on the surface. It is believed to have originated in bats, which serve as natural reservoirs for many coronaviruses. The virus is thought to have been transmitted from bats to civet cats, which acted as intermediate hosts before infecting humans in live-animal markets in Guangdong Province, China, in late 2002.
SARS-CoV was officially identified by scientists in early 2003 after extensive virological investigations. The discovery revealed a novel coronavirus with genetic sequences distinct from previously known human coronaviruses, such as those causing common colds.

Structure and Characteristics

The SARS coronavirus is an enveloped, positive-sense, single-stranded RNA virus with a genome size of approximately 29.7 kilobases, one of the largest among RNA viruses. Its structure includes several key proteins:

• Spike (S) protein: Responsible for binding to the angiotensin-converting enzyme 2 (ACE2) receptor on human cells, facilitating viral entry.
• Envelope (E) protein: Involved in virus assembly and release.
• Membrane (M) protein: Provides shape and stability to the viral envelope.
• Nucleocapsid (N) protein: Encapsulates the RNA genome, protecting it within the viral particle.

The spike protein’s affinity for ACE2 receptors, particularly in lung tissue, explains the virus’s ability to cause severe respiratory symptoms.

Transmission and Epidemiology

SARS spreads primarily through respiratory droplets produced when an infected person coughs or sneezes. It can also spread via direct contact or contaminated surfaces. The virus remains viable for several hours in the environment, which increases transmission potential.
The outbreak of 2002–2003 began in southern China and rapidly expanded to Hong Kong, Vietnam, Singapore, Canada, and several other countries. According to the World Health Organization (WHO), SARS affected more than 8,000 people across 26 countries, resulting in 774 deaths, yielding a case fatality rate of about 9.6%. Older adults and healthcare workers were among the most severely affected groups.
Effective containment was achieved through strict quarantine measures, contact tracing, and international cooperation, and by July 2003, the outbreak was declared contained.

Symptoms and Clinical Manifestations

The incubation period for SARS ranges from 2 to 10 days. The disease typically begins with non-specific flu-like symptoms, which can progress to severe respiratory distress. Common symptoms include:

• High fever (above 38°C)
• Chills and rigours
• Headache and muscle pain
• Dry cough
• Shortness of breath
• Diarrhoea (in some cases)

In severe cases, patients develop pneumonia and acute respiratory distress syndrome (ARDS), which may lead to respiratory failure and death.

Diagnosis and Laboratory Detection

Diagnosis of SARS is based on clinical symptoms combined with laboratory tests to confirm infection. Diagnostic methods include:

• Reverse transcription polymerase chain reaction (RT-PCR): Detects viral RNA in respiratory secretions or blood.
• Serological tests: Identify antibodies against SARS-CoV, indicating past infection.
• Viral culture and sequencing: Used primarily for research purposes.

During the outbreak, WHO and other laboratories collaborated to develop rapid diagnostic tools, allowing for earlier detection and isolation of cases.

Treatment and Management

There is no specific antiviral treatment for SARS. Management is largely supportive, focusing on maintaining adequate oxygenation and hydration while managing symptoms. Interventions include:

• Oxygen therapy and mechanical ventilation for severe cases.
• Use of broad-spectrum antibiotics to prevent secondary bacterial infections.
• Corticosteroids were used experimentally to reduce inflammation, although their effectiveness remained uncertain.

Intensive infection control measures were essential in hospital settings, as healthcare workers were among the most at-risk populations during the epidemic.

Research and Vaccine Development

Following the outbreak, research intensified into understanding coronaviruses and developing potential vaccines. Several vaccine candidates targeting the S protein were tested in animals, but no licensed vaccine for SARS was ultimately released because the outbreak ended before clinical trials could be completed.
However, this research became foundational for the rapid development of vaccines against SARS-CoV-2 in 2020, as the two viruses share significant genetic and structural similarities.

Global Impact and Lessons Learned

The SARS outbreak prompted a major overhaul in global epidemic preparedness and response systems. It led to the establishment of new international health regulations and improved global surveillance networks. Lessons learned from SARS contributed to:

• Faster identification and sequencing of novel pathogens.
• Enhanced global cooperation through WHO-led initiatives.
• Increased emphasis on transparency and timely reporting of disease outbreaks.

SARS also influenced the creation of emergency response frameworks used during the COVID-19 pandemic, illustrating how the earlier crisis helped shape modern pandemic management.

Relationship to Other Coronaviruses

SARS-CoV is closely related to other zoonotic coronaviruses that cause severe respiratory illnesses in humans. Its counterparts include:

• MERS-CoV (Middle East Respiratory Syndrome Coronavirus): Identified in 2012 in Saudi Arabia, also originating from bats but transmitted via camels.
• SARS-CoV-2: Emerged in late 2019, causing the COVID-19 pandemic.

Genetic analysis shows that SARS-CoV and SARS-CoV-2 share approximately 80% genome similarity, explaining many overlapping features in pathogenesis and transmission.

Decline and Containment

By mid-2003, effective international cooperation, early isolation of cases, and strict travel advisories brought the epidemic under control. A few isolated laboratory-acquired infections occurred between 2003 and 2004, but no sustained community transmission was recorded thereafter.