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Let\u2019s start with a medical dictionary definition of a virus: \u201cOne of a group of minute infectious agents\u2026characterized by a lack of independent metabolism and by the ability to replicate only within living host cells. Like living organisms, they are able to reproduce with genetic continuity and the possibility of mutation.\u201d Viruses are responsible for multiple human diseases including polio, mumps, measles, rubella, influenza, and hepatitis \u2014 many of which we see only rarely since the advent of immunizations, which produce a lasting immune response without causing infection. Hepatitis B and HPV (human papilloma virus) are examples of viruses that can sometimes cause cancer (cancer of the liver and cervix, respectively).<\/p>\n
Coronaviruses are a family of viruses that cause disease in mammals and birds. In humans, coronaviruses cause diseases that vary from the common cold to potentially lethal diseases such as SARS, MERS, and the new human disease called COVID-19. The virus that causes COVID-19 is officially called SARS-CoV-2 \u2014 the 2 because it\u2019s the second SARS virus that has been discovered.<\/p>\n
SARS-CoV-2 originated in China. At first it was thought to have originated in a market in Wuhan, but now some experts think it originated in bats. Human-to-human transmission occurs by respiratory droplets when someone within 6 feet of another person coughs or sneezes. The virus can live on various surfaces from minutes to days, depending on the surface. If someone touches a surface with live virus particles, and then they touch their face, the virus can enter their respiratory tract via their nose or mouth. Once in a person\u2019s respiratory tract, the virus sometimes travels down the trachea (windpipe) to the lungs.<\/p>\n
The trachea branches multiple times and at the ends of the final, smallest branches are minute air sacs called alveoli. There are 600 million alveoli in a person\u2019s lungs, and this is where oxygen transfers from the lungs into the bloodstream, and carbon dioxide exits. The CoV-2 replicates in the lungs, and the millions of viral particles that result attack the alveoli, causing an inflammatory response, which in turn results in swelling and fluid in and around the alveoli. Oxygen and carbon dioxide exchange become impaired, and the lungs become stiff and fail to contract and expand easily with breathing. This condition is called acute respiratory distress syndrome (ARDS).<\/p>\n
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