SARS-CoV-2

SARS-CoV-2
Name	SARS-CoV-2
Caption	Illustration of the virus structure
Taxon	Severe acute respiratory syndrome coronavirus 2
Order	Nidovirales
Family	Coronaviridae
Subfamily	Orthocoronavirinae
Genus	Betacoronavirus
Subgenus	Sarbecovirus
Species	Severe acute respiratory syndrome-related coronavirus
Virus group	Group IV ((+)ssRNA)

SARS-CoV-2. It is the virus responsible for the global COVID-19 pandemic, first identified in Wuhan, Hubei, China in late 2019. The virus is a member of the Coronaviridae family and is closely related to the virus that caused the SARS outbreak of 2002-2004. Its rapid worldwide spread led to a profound public health crisis, impacting global healthcare systems, economies, and daily life, and prompting unprecedented international scientific collaboration.

Virology

SARS-CoV-2 is an enveloped, positive-sense single-stranded RNA virus. Its genome is approximately 30,000 nucleotides long, one of the largest among RNA viruses, and is organized with genes for both structural and non-structural proteins. Key structural proteins include the spike protein (S), which facilitates entry into host cells by binding to the angiotensin-converting enzyme 2 (ACE2) receptor, the membrane protein (M), the envelope protein (E), and the nucleocapsid protein (N) which packages the RNA. The virus is classified within the Betacoronavirus genus and the Sarbecovirus subgenus, sharing a common ancestor with bat coronaviruses like RaTG13, identified by researchers at the Wuhan Institute of Virology. The viral life cycle involves replication in the host cell's cytoplasm, utilizing a complex replication-transcription complex.

Transmission and infection

Primary transmission occurs through respiratory droplets and aerosols expelled by infected individuals during activities like coughing, sneezing, or speaking. The virus can also spread via fomites on contaminated surfaces, though this is considered a less common route. Upon inhalation, the spike protein engages with ACE2 receptors abundantly expressed on cells in the respiratory tract, particularly type II pneumocytes in the lungs, but also on cells in the heart, kidneys, and intestines. The infection can range from asymptomatic to severe, with the incubation period typically between 2 to 14 days. Superspreading events, such as those documented on the Diamond Princess cruise ship or at gatherings in Daegu, South Korea, have been a significant feature of its epidemiology.

Variants

As the virus replicates, random mutations in its RNA genome have given rise to numerous genetic lineages with differing characteristics. Key variants, designated as Variants of Concern by the World Health Organization and the Centers for Disease Control and Prevention, have shown increased transmissibility, immune evasion, or virulence. Notable examples include the Alpha variant (B.1.1.7) first sequenced in the United Kingdom, the Beta variant (B.1.351) identified in South Africa, the Gamma variant (P.1) associated with Manaus, Brazil, and the highly transmissible Delta variant (B.1.617.2) which fueled major waves in India and globally. The ongoing evolution of the virus is monitored globally through initiatives like GISAID.

Disease: COVID-19

The disease caused by SARS-CoV-2 is named COVID-19 (Coronavirus Disease 2019). Clinical manifestations are highly variable, including fever, cough, fatigue, and loss of taste or smell (anosmia). Severe cases can progress to pneumonia, acute respiratory distress syndrome (ARDS), and multi-organ failure. Significant long-term sequelae, often termed Long COVID or Post-acute sequelae of SARS-CoV-2 infection (PASC), can involve persistent fatigue, cognitive dysfunction ("brain fog"), and cardiovascular issues. The disease has shown a higher risk of severe outcomes in older adults and individuals with comorbidities like diabetes, hypertension, and obesity.

Diagnosis and testing

Diagnosis primarily relies on detecting viral RNA via reverse transcription polymerase chain reaction (RT-PCR) tests from nasopharyngeal or saliva samples, considered the gold standard. Rapid antigen tests, which detect viral proteins, offer quicker results for screening but are generally less sensitive. Serological tests that detect antibodies against the virus, such as IgG and IgM, are used to identify past infections and study seroprevalence. Diagnostic protocols and test approvals have been managed by agencies like the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA).

Prevention and control

Prevention strategies have included public health measures such as mask mandates, social distancing, quarantine protocols, and contact tracing efforts. The development and deployment of vaccines represented a critical turning point, with platforms including mRNA vaccines (Pfizer-BioNTech, Moderna), viral vector vaccines (Oxford-AstraZeneca, Janssen), and inactivated vaccines (Sinovac, Sinopharm). Global distribution efforts have been coordinated by mechanisms like COVAX, led by the World Health Organization, Gavi, and the Coalition for Epidemic Preparedness Innovations.

Treatment and management

Treatment depends on disease severity. For mild cases, management is supportive. For hospitalized patients, therapeutics have included corticosteroids like dexamethasone to modulate inflammation, antiviral drugs such as remdesivir, and monoclonal antibody therapies like those developed by Regeneron Pharmaceuticals. Immunomodulators like tocilizumab, an interleukin-6 inhibitor, have been used for severe inflammation. The National Institutes of Health and Infectious Diseases Society of America regularly update treatment guidelines based on evolving clinical trial data from studies like the RECOVERY Trial in the United Kingdom.

Category:Viruses Category:Infectious diseases Category:Pandemics