Biology and Symptoms of COVID-19

In order to be complete, we feel our Mini Medical School Course on Hot Topics in Medicine needs a section on the COVID-19 pandemic. I hope this discussion enables you to apply what you have learned in the Mini Medical School Course to critically think about an evolving global health issue. The COVID-19 pandemic has affected nearly every aspect of our day-to-day lives. In this first video, I will introduce the biology and clinical manifestations, or symptoms, of COVID-19. In the second video, I will cover the diagnosis and treatment of COVID-19. And in the third video, I will discuss prevention and ongoing areas of concern with COVID-19.

COVID-19, or coronavirus disease 2019, started as a cluster of pneumonia cases in December 2019 in Wuhan, a city in the Hubei Province of China. It rapidly spread throughout the world, and on March 11, 2020, the World Health Organization, or the WHO, declared COVID-19 a pandemic. COVID-19 continued to spread across the world in different waves of outbreaks. As of November 9, 2021, the WHO reported over 250 million confirmed cases of COVID-19 and over 5 million deaths globally. The virus that causes COVID-19 is “severe acute respiratory syndrome coronavirus 2”, or SARS-CoV-2. It belongs to the Family Coronavirus, which derives its name from the Latin word corona, meaning crown.

When observed under a microscope, [Advance] the characteristic viral spike proteins appear as crown-like projections that resemble the “solar corona”. The Coronaviruses are RNA viruses, and include SARS-CoV-1 and MERS-CoV, other respiratory viruses that have caused outbreaks. Dr. Cohen speaks about these in the “Emerging Infectious Diseases” video. SARS-Cov-2 spreads directly from person to person via respiratory transmission [Advance]. The virus can infect the cells that line our respiratory tract from our nasal passages all the way down to the alveoli, or small air sacs in our lungs. Viral spike protein allows the virus to gain entry into our cells. Once inside the cell, the virus can rapidly replicate, or make many copies of itself, and thus make loads of viral particles.

These new viral particles go on to infect other cells in our body. The virus can also be aerosolized, or turned into tiny airborne droplets, when we sneeze, cough, or talk. These aerosolized particles can then infect other people who are nearby. COVID-19 has a wide range of clinical manifestations or symptoms, from what we call asymptomatic, which means without symptoms, to critical disease. The incubation period, or the time from infection to the onset of symptoms, for SARS-CoV-2 is on average 5 days. Studies show this can range anywhere from 2-14 days. The viral load increases before symptoms develop.This means even asymptomatic carriers can transmit the virus. Inflammation occurs as the result of an immune response to the virus.

Mild disease is reported in the majority (81 percent) of people. Symptoms of mild disease include cough, fever, myalgias, or muscle aches, gastrointestinal symptoms, and anosmia, or loss of smell. In mild COVID-19, the immune system limits viral activity. The viral load eventually comes down, and the symptoms typically resolve in about two weeks. However, it is possible for infected people to be contagious for 10 days or longer after symptom onset. Severe COVID-19 occurs in about 15% of cases. In severe COVID-19, there is an inappropriate immune response. Viral loads remain elevated for a longer period of time. There is excess inflammation which can cause complications such as acute respiratory distress syndrome (ARDS).

When this happens, patients develop dyspnea, or difficulty breathing, shortness of breath, hypoxia, or low oxygen. This may require such patients to be on a ventilator, a machine that helps them breathe. Other complications as a result of systemic inflammation include thromboembolic events. This is where blood clots travel through the body and can cause events such as pulmonary embolism. Dr. Cohen covered pulmonary embolism in Mini Med Introduction to Medicine, Respiratory Physiology 2. Thromboembolic events can also cause stroke, a topic Dr. Cohen covers in Neuroscience of Mini Med Hot Topics in Medicine. In the worst cases of COVID-19, people can suffer multi-organ failure, or death. There are identified risk factors for severe COVID-19.

We know now that things such as older age, being overweight, smoking, substance use disorders, pregnancy, and current use of immunosuppressive medications puts a person at increased risk for severe COVID-19. Additionally, chronic medical conditions like cancer, neurologic conditions, mental health disorders, heart disease, chronic lung disease, chronic kidney disease, diabetes, HIV, blood or immune disorders, or history of transplantation, increase a person’s risk for getting severe COVID-19. This is not to say a young healthy person won’t get severe COVID-19, but healthier people are at a decreased risk for getting severe COVID-19. Please join me in the next video where I will review current diagnosis and treatment of COVID 19.