Discovery
Coronaviruses were first discovered in the 1930s when an acute respiratory infection of domesticated chickens was shown to be caused by the infectious bronchitis virus (IBV). In the 1940s, two more animal coronaviruses, mouse hepatitis virus (MHV) and transmissible gastroenteritis virus (TGEV), were isolated. Human coronaviruses were discovered in the 1960s. The earliest ones studied were from human patients with the common cold, which was later named human coronavirus 229E and human coronavirus OC43.[11] Other human coronaviruses have since been identified, including SARS-CoV in 2003, HCV NL63 in 2004, HKU1 in 2005, MERS-CoV in 2012, and SARS-CoV-2 in 2019. Most of these have involved severe respiratory tract infections.
Etymology
The name "coronavirus" is derived from Latin corona, meaning "crown" or "wreath," itself a borrowing from Greek κορώνη korṓnē, "garland, wreath." The name refers to the characteristic appearance of virions (the infective form of the virus) by electron microscopy, which has a fringe of large, bulbous surface projections creating an image reminiscent of a crown or a solar corona. This morphology is created by the viral spike peplomers, which are proteins on the surface of the virus.
Morphology
The cross-sectional model of a coronavirus Coronaviruses is large pleomorphic spherical particles with bulbous surface projections. The average diameter of the virus particles is around 120 nm (.12 μm). The width of the envelope is ~80 nm (.08 μm), and the spikes are ~20 nm (.02 μm) long. The container of the virus in electron micrographs appears as a distinct pair of electron-dense shells. The viral envelope consists of a lipid bilayer where the membrane (M), envelope (E), and spike (S) structural proteins are anchored. A subset of coronaviruses (individually the members of betacoronavirus subgroup A) also has a shorter spike-like surface protein called hemagglutinin esterase (HE). Inside the envelope, there is the nucleocapsid, which is formed from multiple copies of the nucleocapsid (N) protein, which are bound to the positive-sense single-stranded RNA genome in a continuous beads-on-a-string type conformation. The lipid bilayer envelope, membrane proteins, and nucleocapsid protect the virus when it is outside the host cell.
Genome
See also: Severe acute respiratory syndrome-related coronavirus § Genome Schematic representation of the genome organization and functional domains of S protein for SARS-CoV and MERS-CoV Coronaviruses contains a positive-sense, single-stranded RNA genome. The genome size for coronaviruses ranges from 26.4 to 31.7 kilobases. The genome size is one of the largest among RNA viruses. The genome has a 5′ methylated cap and a 3′ polyadenylated tail. The genome organization for a coronavirus is 5′-leader-UTR-replicase/transcriptase-spike (S)-envelope (E)-membrane (M)-nucleocapsid (N)-3′UTR-poly (A) tail. The open reading frames 1a and 1b, which occupy the first two-thirds of the genome, encode the replicase/transcriptase polyprotein. The replicase/transcriptase polyprotein self cleaves to form nonstructural proteins. The later reading frames encode the four major structural proteins: spike, envelope, membrane, and nucleocapsid. Interspersed between these reading frames are the reading frames for the accessory proteins. The number of accessory proteins and their function is unique, depending on the specific coronavirus.
Reported illnesses have ranged from mild symptoms to severe illness and death for certain coronavirus disease 2019 (COVID-19) cases. These symptoms may appear 2-14 days after exposure (based on the incubation period of MERS-CoV viruses). Fever Cough Shortness of breath. When to Seek Medical Attention If you develop emergency warning signs for COVID-19, get medical attention immediately. Emergency warning signs include*: Trouble breathing Persistent pain or pressure in the chest New confusion or inability to arouse Bluish lips or face respiratory protection program managers, leaders in occupational health services and infection prevention and control programs, and other leaders in healthcare settings who are responsible for developing and implementing policies and procedures for preventing pathogen transmission in healthcare settings. Purpose: This document offers a series of strategies or options to optimize supplies of disposable N95 filtering facepiece respirators (commonly called "N95 respirators") in healthcare settings when there is a limited supply. It does not address other aspects of pandemic planning; for those, healthcare facilities can refer to COVID-19 preparedness plans. The strategies are also listed in order of priority and preference in the Checklist for Healthcare Facilities: Strategies for Optimizing the Supply of N95 Respirators during the COVID-19 Response in an easy-to-use format for healthcare facilities. hierarchy of controls (from most to least effective): Elimination, Substitution, Engineering Controls, Administration Controls, PPE. Controlling exposures to occupational hazards is a fundamental way to protect personnel. Conventionally, a hierarchy has been used to achieve feasible and effective controls. Multiple control strategies can be implemented concurrently and or sequentially. This hierarchy can be represented as follows: Elimination Substitution Engineering controls Administrative controls Personal protective equipment (PPE) To prevent infectious disease transmission, elimination (physically removing the hazard) and substitution (replacing the hazard) are not typically options for healthcare settings. However, exposures to transmissible respiratory pathogens in healthcare facilities can often be reduced or possibly avoided through engineering and administrative controls and PPE. Prompt detection and effective triage and isolation of potentially infectious patients are essential to prevent unnecessary exposures among patients, healthcare personnel (HCP), and visitors at the facility. N95 respirators are the PPE most often used to control exposures to infections transmitted via the airborne route, though their effectiveness is highly dependent upon proper fit and use. The optimal way to prevent airborne transmission is to use a combination of interventions from across the hierarchy of controls, not just PPE alone. Applying a combination of controls can provide an additional degree of protection, even if one intervention fails or is not available. Respirators, when required to protect HCP from airborne contaminants such as some infectious agents, must be used in the context of a comprehensive, written respiratory protection program that meets the requirements of OSHA's Respiratory Protection standard external icon. The program should include medical evaluations, training, and fit testing. Surge capacity refers to the ability to manage a sudden, unexpected increase in patient volume that would otherwise severely challenge or exceed the present capacity of a facility. While there are no commonly accepted measurements or triggers to distinguish surge capacity from daily patient care capacity, surge capacity is a useful framework to approach a decreased supply of N95 respirators during the COVID-19 Response. Three general strata have been used to describe surge capacity and can be used to prioritize measures to conserve N95 respirator supplies along the continuum of care.1 Current capacity: measures consist of providing patient care without any change in daily contemporary practices. This set of measures, consisting of engineering, administrative, and PPE controls, should already be implemented in general infection prevention and control plans in healthcare settings. Contingency capacity: measures may change standard daily practices but may not have any significant impact on the care delivered to the patient or the safety of HCP. These practices may be used temporarily during periods of expected N95 respirator shortages. Crisis capacity: strategies that are not commensurate with U.S. standards of care. These measures, or a combination of these measures, may need to be considered during periods of known N95 respirator shortages. Conventional Capacity Strategies (should be incorporated into everyday practices) Engineering Controls reduce exposures for HCP by placing a barrier between the hazard and the HCP. Engineering controls can be very effective as part of a suite of strategies to protect HCP without placing primary responsibility of implementation on them (i.e., they function without HCP having to take any action).
You must be logged in to post a comment.