- 120 nm in diameter
- Usually distinguished by its club-shaped or “crown-like” surface proteins
- Enveloped, with the viral envelope containing the following proteins:
- Spike (S) protein
- Hemagglutinin esterase (HE) protein
- Membrane (M) protein
- Envelope (E) protein
- The nucleocapsid is large and has helical symmetry.
- Has a single-stranded RNA genome of approximately 26–31 kilobases
Clinically relevant species
- The family Coronaviridae comprises 2 subfamilies:
- Letovirinae (has no medically relevant species)
- Orthocoronavirinae is divided into 4 genera:
- Alphacoronavirus and Betacoronavirus (infect mammals)
- Gammacoronavirus and Deltacoronavirus (mainly infect birds)
- Most of the human-infecting species of coronavirus are found within the Betacoronavirus genus. The most relevant ones include:
- Human coronaviruses (HCoV-OC43, HCoV-HKU1, HCoV-2293)
- Severe acute respiratory syndrome coronavirus (SARS-CoV)
- Middle East respiratory syndrome-related coronavirus (MERS-CoV)
- Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)
- Chiroptera (bats) are thought to be the origin host for all alphacoronaviruses and betacoronaviruses and, therefore, all human coronaviruses.
- Camels can also be a reservoir for MERS.
- Birds are the natural reservoirs and hosts for all of the gammacoronaviruses and deltacoronaviruses.
- Routes of transmission:
- Respiratory droplets and airborne spread
- Contact with infected surfaces and fomites
- Vertical transmission has been reported for SARS-CoV-2.
Most coronaviruses have 4 structural proteins: S, E, M, and N.
- S, E, and M proteins create the viral envelope.
- The N protein forms a complex with RNA (nucleocapsid) and aids in the regulation of viral RNA synthesis.
- The M protein projects on the external surface of the envelope and is important for viral assembly.
- The E protein has an unclear function, although it may aid in virus release.
- The S protein is a club-shaped surface projection that gives the virus its characteristic crown-like appearance on electron microscopy and is responsible for receptor binding and fusion with the host cell membrane.
- Coronaviruses bind to the host cell surface via the S proteins.
- Viral entry occurs either by receptor-mediated endocytosis or through membrane fusion.
- The virus escapes the acidified environment of the endosomes by transporting itself to lysosomes.
- Coronaviruses have single-stranded, positive-sense RNA that can directly produce the proteins and new genomes in the cytoplasm.
- The negative-sense strand template RNA is produced.
- The new viral proteins are translated by the host’s ribosomes.
- The nucleocapsid protein binds with genomic RNA, and protein M is integrated into the membrane of the endoplasmic reticulum along with proteins S and HE.
- An assembled nucleocapsid that contains the RNA moves into the endoplasmic reticulum to be encased and is released by exocytosis.
Diseases Caused by Coronaviruses
- Common cold:
- The common cold is usually caused by rhinoviruses.
- However, coronaviruses cause 15% of common colds.
- Incubation period: 3 days
- GI infections:
- Far less commonly caused by coronaviruses
- Incubation period: 3 days
- Usually presents as a very mild infection that causes diarrhea, diffuse abdominal pain, and vomiting
- Rarely, can lead to neonatal necrotizing enterocolitis
- Emerged in 2012 in Saudi Arabia from dromedary camels.
- Incubation period: 5 days
- Clinical presentation ranges from asymptomatic infection to acute upper respiratory illness.
- Can lead to rapidly progressive pneumonitis, respiratory failure, septic shock, and multiorgan failure, resulting in death.
- Emerged in 2003 in southern China from civet cats.
- Incubation period: 4–6 days
- Clinical presentation ranges from mild, flu-like illness with full recovery (25% of cases), to severe respiratory infection (approximately 70%), to death from respiratory failure (approximately 10%).
- Usually manifests as low-grade fever, muscle pain, lethargy, cough, sore throat, and malaise
- Can progress to dyspnea, pneumonia, respiratory failure, and death
- Coronavirus disease 2019 (COVID-19):
- Emerged in November 2019 in Wuhan, China, from horseshoe bats and caused a global pandemic
- Incubation period: 2–14 days
- Clinical presentation can range from asymptomatic or mild infections will full recovery (80% of cases), to severe respiratory infections (15%), to critical disease with multiorgan damage (5%) and death (2.2%).
- Usually presents as dry cough, malaise, and fatigue and may be associated with hemoptysis, diarrhea, vomiting, headache, anosmia, dysgeusia, and chest pain
- Can progress to pneumonia, ARDS, thrombosis, sepsis, multiorgan failure, and death
|Date of first identified case||June 2012||November 2002||December 2019|
|Location of first identified case||Jeddah, Saudi Arabia||Shunde, China||Wuhan, China|
|Average age||56 years||44 years||56 years|
|Sex ratio (M:F)||3.3:1||0.8:1||1.6:1|
|MERS (caused by MERS-CoV)||SARS (caused by SARS-CoV)||COVID-19 (caused by SARS-CoV-2)|
Comparison of Similar Viruses
|Diagnosis||Clinical diagnosis||Clinical diagnosis|
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