Microbiology
Summary
Coronaviruses are enveloped, single-stranded, positive-sense RNA viruses viruses characterized by helical nucleocapsids. This family encompasses both low-pathogenicity coronaviruses responsible for the common cold, which are endemic in humans, and high-pathogenicity coronaviruses like SARS-CoV, MERS-CoV, and SARS-CoV-2 (COVID-19), which are zoonotic with bats as primary hosts. These enveloped viruses have membrane (M), envelope (E), and spike (S) proteins integrated into their envelope, with the S glycoprotein heavily glycosylated.
SARS-CoV-2 enters host cells by binding ACE2 receptors on the cell surface. Replication involves translating the replicase gene's positive-sense genomic RNA into long polyproteins, then releasing proteases through autoproteolytic cleavage. The RdRp enzyme synthesizes negative-sense RNA from genomic RNA, forming new positive-sense RNA strands. Assembled virions include a nucleocapsid formed in the cytoplasm, while S, M, and E proteins are transported to the Golgi for packaging, leading to viral budding. Transmission occurs via airborne or droplet routes, and COVID-19, caused by SARS-CoV-2, can manifest as an asymptomatic carrier state or with common symptoms like cough and fever. Severe cases may lead to pneumonia and acute respiratory distress syndrome (ARDS). Nucleic acid amplification tests (NAATs) on nasopharyngeal swabs detect viral RNA, and serologic assays provide information about infection history.
Lesson Outline
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FAQs
Coronaviridae, commonly known as coronaviruses, are a type of virus featuring a core of genetic material surrounded by an envelope with protein spikes. This structure gives the appearance of a crown, hence the name "corona". The genetic material of coronaviruses is a single-stranded RNA. The viral envelope consists of lipids and includes proteins such as the spike (S), envelope (E), and membrane (M) proteins that assist in the virus's functionality and transmission.
COVID-19, SARS (severe acute respiratory syndrome), and MERS (Middle East respiratory syndrome) are all diseases caused by viruses within the Coronaviridae family. They share similarities, such as being respiratory illnesses with symptoms including fever, cough, and difficulty breathing. However, the viruses that cause these diseasesÑSARS-CoV-2 (COVID-19), SARS-CoV (SARS), and MERS-CoV (MERS)Ñhave differences in their severity, transmission rate, and geographic occurrence.
The ACE2 receptor plays a crucial role in the transmission of SARS-CoV-2, the virus causing COVID-19. The spike protein on the surface of SARS-CoV-2 can attach to the ACE2 receptor, allowing the virus to enter and infect human cells, starting the infection process. While ACE2 receptors are present in various cells throughout the body, including the lungs, heart, kidneys, and gastrointestinal tract, it's important to note that the virus has a higher affinity for ACE2 receptors in the respiratory tract and lungs.
The key symptoms of COVID-19 range from mild symptoms to severe illness and they may appear 2-14 days after exposure to the virus. These symptoms include fever, cough, shortness of breath, fatigue, body aches, loss of taste or smell, and more. Testing for COVID-19 primarily involves collection of a respiratory specimen, generally from the nose or throat, via a nasopharyngeal swab. This sample is then tested for the presence of SARS-CoV-2 RNA.
The virus enters host cells by attaching to ACE2 receptors on the cell surface. Upon entry, the replicase gene's positive-sense genomic RNA is translated into long polyproteins. Proteases are then released through autoproteolytic cleavage. The RdRp enzyme facilitates the synthesis of negative-sense RNA from the viral genomic RNA, resulting in the creation of new positive-sense RNA strands. Assembled virions include a nucleocapsid formed in the cell's cytoplasm. Meanwhile, spike (S), membrane (M), and envelope (E) proteins are transported to the Golgi apparatus for packaging. This packaging process leads to viral budding, where new virions are released from the host cell. This cycle enables the virus to replicate, spread, and infect other cells.
