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Coronaviruses are a group of viruses that cause diseases in mammals and birds. In humans, the viruses cause respiratory infections – including the common cold – which are typically mild. Rarer forms such as SARS, MERS and the novel coronavirus causing the 2019–20 Wuhan coronavirus outbreak can be lethal. In cows and pigs coronaviruses cause diarrhea. In chickens they cause an upper respiratory disease. No vaccines or antiviral drugs are approved for prevention or treatment.
Coronaviruses are in the subfamily Orthocoronavirinae in the family Coronaviridae, in the order Nidovirales. They are enveloped viruses with a positive-sense single-stranded RNA genome and a nucleocapsid of helical symmetry. The genome size of coronaviruses ranges from approximately 26 to 32 kilobases, the largest for an RNA virus.
The name "coronavirus" is derived from the Latin corona, meaning crown or halo, which refers to the characteristic appearance of the virus particles (virions): they have a fringe reminiscent of a crown or of a solar corona.
The 2019 novel coronavirus (provisionally named 2019-nCoV), informally known as the Wuhan coronavirus, is a contagious virus that causes 2019-nCoV acute respiratory disease, a respiratory infection. It is the cause of the ongoing 2019–20 Wuhan coronavirus outbreak and has been designated a global health emergency by the World Health Organization. Genomic sequencing has shown that it is a positive-sense, single-stranded RNA coronavirus.
Many early cases were linked to a large seafood and animal market, and the virus is thought to have a zoonotic origin. Comparisons of the genetic sequences of this virus and other virus samples have shown similarities to SARS-CoV (79.5%) and bat coronaviruses (96%). This makes an ultimate origin in bats likely, although an intermediate host, such as a pangolin, cannot be ruled out.
Human-to-human transmission of the virus has been confirmed. Coronaviruses are primarily spread through close contact, in particular through respiratory droplets from coughs and sneezes within a range of about 6 feet (1.8 m). Viral RNA has also been found in stool samples from infected patients. It is possible that the virus can be infectious even during the incubation period, but this has not been proven, and the World Health Organization (WHO) states that "transmission from asymptomatic cases is likely not a major driver of transmission" at this time.
During the ongoing outbreak, the virus has often been referred to in common parlance as "the coronavirus", "the new coronavirus" and "the Wuhan coronavirus", while the WHO recommends the temporary designation "2019-nCoV". Amid concerns that the absence of an official name may lead to the use of prejudicial informal names, per 2015 WHO guidelines, the International Committee on Taxonomy of Viruses (ICTV) has announced that it will introduce a suitable official name for the virus in the second week of February 2020.
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