ជំងឺកូរ៉ូណាវីរុស២០១៩: Cause

Cause

ការចំលង

alt=Cough/sneeze droplets visualised in dark background using Tyndall scattering|thumb|Respiratory droplets produced when a man sneezes, visualised using Tyndall scattering
thumb|thumbtime=4:02|A video discussing the basic reproduction number and case fatality rate in the context of the pandemic

COVID-19 is a new disease, and the ways it spreads between people are under investigation, including: the role of small droplets, the extent and how it may be transmitted through air, and how long the virus remains infectious on surfaces. The disease is spread during close contact, often by small droplets produced during coughing, sneezing, or talking. During close contact, (1 to 2 metres, 3 to 6 feet), people catch the disease after breathing in contaminated droplets that were exhaled by infected people. However, the droplets are relatively heavy and usually fall to the ground or surfaces, as opposed to being infectious over large distances.

After the droplets fall to floors or surfaces, they still can infect other people, if they touch contaminated surfaces and then their eyes, nose or mouth with unwashed hands. On surfaces the amount of active virus decreases over time until it can no longer cause infection. However, experimentally, the virus can survive on various surfaces for some time, (for example copper or cardboard for a few hours, and plastic or steel for a few days). Surfaces are easily decontaminated with household disinfectants which kill the virus outside the human body or on the hands. Disinfectants or bleach are not a treatment for COVID-19, and cause health problems when not used properly, such as inside the human body.

Sputum and saliva carry large amounts of virus. Some medical procedures may result in the virus being transmitted easier than normal for such small droplets, known as airborne transmission.

The virus is most contagious during the first three days after onset of symptoms, although spread is known to occur up to two days before symptoms appear (presymptomatic transmission) and in later stages of the disease.Coronavirus disease 2019 (COVID-19) in the EU/EEA and the UK – ninth update, 23 April 2020. Stockholm: ECDC, p.8-9. Some people have been infected and recovered without showing symptoms, but uncertainties remain in terms of asymptomatic transmission.

Although COVID-19 is not a sexually transmitted infection, kissing, intimate contact, and faecal oral routes are suspected to transmit the virus.

វីរុសវិទ្យា

thumb|Illustration of SARSr-CoV virion

Severe acute respiratory syndrome coronavirus2 (SARS-CoV-2) is a novel severe acute respiratory syndrome coronavirus, first isolated from three people with pneumonia connected to the cluster of acute respiratory illness cases in Wuhan. All features of the novel SARS-CoV-2 virus occur in related coronaviruses in nature.
Outside the human body, the virus is killed by household soap, which bursts its protective bubble.

SARS-CoV-2 is closely related to the original SARS-CoV. It is thought to have a zoonotic origin. Genetic analysis has revealed that the coronavirus genetically clusters with the genus Betacoronavirus, in subgenus Sarbecovirus (lineage B) together with two bat-derived strains. It is 96% identical at the whole genome level to other bat coronavirus samples (BatCov RaTG13). In February 2020, Chinese researchers found that there is only one amino acid difference in the binding domain of the S protein between the coronaviruses from pangolins and those from humans; however, whole-genome comparison to date found that at most 92% of genetic material was shared between pangolin coronavirus and SARS-CoV-2, which is insufficient to prove pangolins to be the intermediate host.