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COVID‑19 pathogenesis. The SARS-CoV-2 virus can infect a wide range of cells and systems of the body. COVID‑19 is most known for affecting the upper respiratory tract (sinuses, nose, and throat) and the lower respiratory tract (windpipe and lungs). [125]
SARS-CoV-2 is the seventh known coronavirus to infect people, after 229E, NL63, OC43, HKU1, MERS-CoV, and the original SARS-CoV. [105] Like the SARS-related coronavirus implicated in the 2003 SARS outbreak, SARS‑CoV‑2 is a member of the subgenus Sarbecovirus (beta-CoV lineage B). [106] [107] Coronaviruses undergo frequent recombination. [108]
The human coronavirus discovered in 2003, SARS-CoV, which causes severe acute respiratory syndrome (SARS), has a unique pathogenesis because it causes both upper and lower respiratory tract infections.
The COVID-19 vaccines are widely credited for their role in reducing the severity and death caused by COVID-19. [ 128 ] [ 129 ] As of March 2023, more than 5.5 billion people had received one or more doses [ 130 ] (11.8 billion in total) in over 197 countries.
The transmission of COVID-19 is the passing of coronavirus disease 2019 from person to person. COVID-19 is mainly transmitted when people breathe in air contaminated by droplets/aerosols and small airborne particles containing the virus. Infected people exhale those particles as they breathe, talk, cough, sneeze, or sing.
SARS-CoV-2, the causative agent of COVID-19, was first introduced to humans through zoonosis (transmission of a pathogen to a human from an animal), and a zoonotic spillover event is the origin of SARS-CoV-2 that is considered most plausible by the scientific community.
The envelope (E) protein is the smallest and least well-characterized of the four major structural proteins found in coronavirus virions. [2] [3] [4] It is an integral membrane protein less than 110 amino acid residues long; [2] in SARS-CoV-2, the causative agent of Covid-19, the E protein is 75 residues long. [5]
Coronavirus diseases are caused by viruses in the coronavirus subfamily, a group of related RNA viruses that cause diseases in mammals and birds. In humans and birds, the group of viruses cause respiratory tract infections that can range from mild to lethal.