**3. COVID-19**

Coronaviruses are a large family of viruses that can cause mild illnesses, such as the common cold, to more severe diseases such as Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS). Coronaviruses take their names from the distinctive spikes with rounded tips around their surface, which reminded virologists of the appearance of the sun's atmosphere, known as corona. Coronaviruses are known to primarily target the human respiratory system. COVID-19 represents the seventh member of the coronavirus family that infects humans. Because the novel coronavirus is related to the SARS-associated coronavirus (SARS-CoV), the virus has been named SARS-CoV2. SARS-CoV2 infection may result in mild to severe symptoms that may develop between 2 and 14 days after exposure to the SARS-CoV2 virus. The symptoms of COVID-19 may include shortness of breath, chills, fever, cough, headaches, sore throat, and loss of taste or smell. Additional symptoms including aches, fatigue, nasal congestion and diarrhea may also appear. The illness may cause severe pneumonia and heart problems in some people and may also lead to death. Some people may not develop any symptoms following infection.

SARS-CoV2, by using the spike-like protein on its surface, binds to ACE2 (Angiotensin converting enzyme 2) prior to entry and infection into the host cell. Thus, ACE2 acts as a doorway for the virus that causes COVID-19. ACE2 is a carboxypeptidase enzyme present on the surface of many cell types in tissues like, lungs, heart, blood vessels, kidneys, liver and gastrointestinal tract. The function of ACE2 is to generate small peptides/proteins by cutting up the larger protein angiotensin which then go on to regulate functions in the cells involving wound healing, inflammation and blood pressure regulation, etc.
