Coronaviruses are enveloped RNA viruses. The characteristic surface of a coronavirus virion has a crown-like appearance that can be seen under the electron microscope. ​ Most coronaviruses infect animals (i.e. bats, birds and mammals), which act as reservoirs and intermediate hosts, but can sometimes change host and infect humans.​ There are currently 7 coronaviruses known to infect humans, four of them causing mild-to-moderate disease in most people (HCoV-OC43, HCoV-HKU1 and HCoV-229E, HCoV-NL63) and three of them cause more severe and possibly even fatal disease

• SARS-CoV, responsible for severe acute respiratory syndrome (SARS) (2002).
• MERS-CoV, responsible for Middle East respiratory syndrome (MERS) (2012).
• SARS-CoV-2, responsible for coronavirus disease 2019 (COVID-19) (2019).

 

Coronaviruses are transmitted through the inhalation of or direct contact with respiratory droplets from an infected individual (including aerosols generated through sneezing, coughing, speaking, singing, or breathing).

Symptoms may vary, both in frequency and severity, depending on several factors (e.g. the variant, the immune status, age, presence of certain disabilities, underlying health conditions). Severe COVID-19 disease usually manifests as pneumonia with shortness of breath and pulmonary infiltrates on chest imaging. Other severe complications include thromboembolism circulatory shock, myocardial damage, arrhythmias, and encephalopathy.