Thread by @CillianDeGascun

#Coronaviruses: an introductory thread/primer. #Coronaviruses are a family of viruses that cause respiratory & intestinal illness in birds, animals, and humans. #2019nCoV is the 7th coronavirus known to infect humans (#HCoV).

Four #HCoVs – OC43, 229E, HKU1 & NL63 – cause mild ‘common cold-like’ illness. All of us have probably been infected with one or more of these at some time. These 4 #HCoVs only occasionally cause serious illness 2/n

The other 2 #HCoVs – #SARS & #MERS – cause severe disease. #SARS emerged in 2012 & infected about 8000 people worldwide with a case fatality rate (CFR) of about 10%. The #SARS outbreak was ultimately controlled with good infection prevention & control procedures 3/n

#SARS is no longer in circulation. #MERS emerged in 2012 and has infected around 2500 people but with a CFR of around 35%: for comparison purposes, the CFR for seasonal #influenza is around 0.1% 4/n

Although it’s too early to definitively ascertain the CFR for #2019nCoV, it seems to be in the region of 3-4%: obviously lower than #SARS/#MERS but significant nonetheless 5/n

Analysis of the virus genome suggests #2019nCoV crossed over into humans in November/December of 2019. Based on a comparison with the genomes of other known viruses, it seems #2019nCoV originated in bats 6/n

However, we don’t yet know if the virus passed through an intermediate host first, although if we can infer anything from #SARS (palm civets) & #MERS (dromedary camels), it probably did 7/n

Humans were originally exposed to the virus at a seafood & live animal market, but it is not known how the virus was transmitted at that location. At this stage, we don’t know how many people were exposed, or how many times #2019nCoV crossed the species barrier 8/n

The virological data suggest that there was either a single #2019nCoV introduction into the human population, or a small number of animal-to-human transmissions of very similar viruses 9/n

As that market has now been closed and disinfected, the fact that the outbreak is continuing & growing suggests that sustained human-to-human transmission is responsible for the majority of new cases 10/n

It has been calculated that each case is infecting between 2 and 3 other people. Obviously, if this pattern continues without intervention, the outbreak will continue to expand. There is no vaccine against #2019nCoV at this time, and no specific antiviral therapy 11/n

Great credit is due to healthcare workers & scientists who are treating patients, contact-tracing, sharing data, & developing diagnostics; & thoughts and prayers with those who are sick and who have already lost family and friends as a result of this outbreak #2019nCoV 12/12

And of course there's a typo in tweet 3 🙄 #SARS emerged in 2002!