Severe acute respiratory syndrome coronavirus

Overview

Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) is a virus that causes severe acute respiratory syndrome (SARS), a viral respiratory illness. It is a member of the Coronaviridae family and the Betacoronavirus genus. SARS-CoV was first identified in 2003 during an outbreak that began in Asia and spread to other continents.

Virology

SARS-CoV is an enveloped virus with a positive-sense, single-stranded RNA genome. The virus is spherical with a diameter of approximately 80-120 nm. The genome of SARS-CoV is approximately 29.7 kb in length, making it one of the largest known RNA genomes.

Genome Structure

The genome of SARS-CoV is organized into several open reading frames (ORFs). The first two-thirds of the genome encodes the replicase proteins, which are involved in viral replication and transcription. The remaining one-third encodes structural proteins, including the spike protein (S), envelope protein (E), membrane protein (M), and nucleocapsid protein (N).

Replication Cycle

The replication cycle of SARS-CoV begins with the attachment of the spike protein to the angiotensin-converting enzyme 2 (ACE2) receptor on the host cell surface. Following attachment, the virus enters the host cell through endocytosis or direct fusion with the cell membrane. Once inside, the viral RNA is released into the cytoplasm, where it is translated into viral proteins. The replicase proteins form a replication-transcription complex that synthesizes a full-length negative-sense RNA template, which is then used to produce new positive-sense genomic RNA and subgenomic mRNAs. These mRNAs are translated into structural proteins, which assemble with the genomic RNA to form new virions. The virions are then released from the host cell to infect new cells.

Transmission

SARS-CoV is primarily transmitted through respiratory droplets produced when an infected person coughs or sneezes. It can also spread through direct contact with infected bodily fluids or surfaces. The virus can survive on surfaces for several hours, making fomite transmission possible.

Clinical Features

The incubation period for SARS-CoV is typically 2-10 days. The illness begins with flu-like symptoms, including fever, myalgia, headache, and malaise. As the disease progresses, patients may develop a dry cough, dyspnea, and pneumonia. In severe cases, acute respiratory distress syndrome (ARDS) and respiratory failure can occur, leading to death.

Diagnosis

Diagnosis of SARS-CoV infection is based on clinical symptoms, epidemiological history, and laboratory tests. Reverse transcription polymerase chain reaction (RT-PCR) is the most common method for detecting viral RNA in respiratory specimens. Serological tests can also be used to detect antibodies against SARS-CoV.

Treatment

There is no specific antiviral treatment for SARS-CoV infection. Management of the disease is primarily supportive, including oxygen therapy, mechanical ventilation, and intensive care for severe cases. Corticosteroids and antiviral drugs have been used in some cases, but their efficacy is not well established.

Prevention

Preventive measures for SARS-CoV include infection control practices such as hand hygiene, wearing personal protective equipment (PPE), and isolating infected individuals. During outbreaks, quarantine and travel restrictions may be implemented to prevent the spread of the virus.

Epidemiology

The SARS outbreak of 2002-2003 affected over 8,000 people worldwide, with a case fatality rate of approximately 9.6%. The outbreak was contained through public health measures, and no new cases have been reported since 2004.

See Also

• Coronavirus
• Middle East respiratory syndrome coronavirus (MERS-CoV)
• COVID-19