The COVID virus's closest known relative was found in bats in Laos
SARS-CoV-2, the virus behind COVID-19, is the seventh coronavirus known to infect people. Its nearest known cousin, BANAL-52, was found in bats in Feuang, Laos, and shares 96.8% of its genome, yet no known virus is its direct ancestor, and exactly how it first reached humans is still unsettled.
It is a positive-sense single-stranded RNA virus of the same species as SARS-CoV-1, which caused the 2002–2004 SARS outbreak. First identified in Wuhan, it was treated by the WHO as a global health emergency, formally a public health emergency of international concern, between January 30, 2020, and May 5, 2023. Its low genetic diversity points to a spillover into humans in late 2019. The International Committee on Taxonomy of Viruses gave it its official name on 11 February 2020, after the WHO had used 2019-nCoV to avoid tying a disease to a place.
Bats are considered the likeliest natural reservoir, but differences from bat viruses suggest a possible intermediate host, and no reservoir has been confirmed. A March 2021 WHO-convened report rated spillover through an intermediate animal as most likely, direct spillover from bats next, and the food chain and Huanan Seafood Market as possible but less likely; a November 2021 analysis argued that the cluster of early cases at the market pointed to it as the source. Pangolins were proposed in 2020, but viruses from seized animals matched only 92% and bind the human ACE2 receptor poorly.
Early estimates put each infection at 2.4–3.4 new cases in a population with no immunity or precautions, and later variants spread faster. The virus moves through close contact, droplets and airborne aerosols, even from speech, and enters cells by binding ACE2. Somewhere between 200 and 800 virus particles are thought to start an infection. Early lab work suggested it lasts up to three days on plastic and steel but under four hours on copper, and soap breaks up its fatty envelope. Much spread happened before symptoms: one study revised its estimate to shedding beginning four to five days early.
Reinfection happens. The first confirmed case, a 33-year-old man in Hong Kong, tested positive again 142 days after his first infection, with sequencing showing a different lineage. The virus also mutates more slowly than influenza, because its replication machinery proofreads the RNA it copies.
Source: SARS-CoV-2
