This page contains resources to understand the exponential growth and emergent propagation that contagious diseases like the COVID-19 virus may exhibit. Some of the resources are specific to the 2020 COVID-19 pandemic, and some are applicable to both historic and future viral outbreaks and pandemics. The evolution of new virus diseases is a normal, expected property of rapidly reproducing viruses. Epidemiologists know that viral pandemics are highly probable events in our future. For that reason it is important for educators, students, parents, leaders, and citizens to be aware of the range of viral events they will encounter in their lifetime.
The generation of a new contagious virus
A virus is a bit of genetic material (RNA or DNA) surrounded by a protein coat. It’s only purpose is to reproduce, but it can’t do that by itself. A virus reproduces by inserting it’s genetic material into a host cell, which may be a bacterium, a plant cell, a fish cell, or a human cell. Only some viruses can attack a human cell; we’re safe from the plant viruses, but viruses that infect other mammals can infect humans if their RNA or DNA mutates to create a new virus with different properties. The infected cell is hijacked to reproduce the virus RNA or DNA, and most of the time cells (yours and all cells) duplicate a genetic strand accurately. But sometimes there are errors. A healthy cell identifies the bad copies and destroys the RNA or DNA strand. Those copies that are not destroyed have “mutated.” Mutation can also be caused by radiation from X-rays, cosmic rays, or ultraviolet light (which can damage skin cells, causing skin cancer). Thousands of new viruses (probably hundreds of thousands) are created every year, but only a few create new “diseases.” Most of the new viruses don’t succeed in transferring to a new host or in attacking cells effectively. These new viruses are random mutations whose emergence and properties cannot be predicted. But the emergence of new contagious viruses is guaranteed by the laws of biology.
Are All Viruses Harmful?
Some viruses live with you for your whole life! Nearly 60% of the world’s population under the age of 50 carry the Herpes Simplex (HSV-1) virus, and most don’t even know they have it. Are they sick or diseased? Sometimes this oral herpes virus may erupt as a “cold sore” on the host’s lip, but most of the time the virus lies dormant in the Trigeminal nerve along the sides of your face (see yellow nerve in image). The HSV-1 virus may actually protect its host from HSV-2 infection (genital herpes) by preparing the immune system to rapidly identify and destroy HSV-2 viruses!
You Probably STILL Have “Chicken Pox!”
If you had Chicken Pox as a child, you carry the virus that caused it is carried with you throughout life, hiding in nerve tissue near the spinal cord and brain. The virus may erupt again later in life as a painful “shingles” attack. When your Chicken Pox ended, the virus remained for decades without causes symptoms or harm until the Shingles attack. Vaccination can prevent Chicken Pox and Shingles by inserting a weaker virus into your system that trains your immune system to quickly recognize the “zoster” virus and kill it (or its resurgence).
Modeling or Simulating the Spread of a Virus Outbreak
A virus outbreak can be modeled using an “agent-based” model because the virus is passed from one individual (agent) to another. It’s not like fog that blankets an area and envelops everyone. It is contagious from one person to another, period (or from what one person touches or when one person coughs to another person). One of the most common agent-based simulation systems is NetLogo from Northwestern University. NetLogo is a free download for Windows or Mac and is also available as an HTML5 web service that is accessible to tablets and Chromebooks with no software installation needed. NetLogo graphically shows its output such as the animated spread of a virus. It included a simple programming language so that students or researchers can modify existing models or build their own. It is useful from 3rd grade through professional researcher!
NetLogo includes hundreds of simulations including a model of how the HIV virus is spread. Each model includes an “Info” page that explains what variables are modeled and how the model works. Here’s the HIV virus link (suitable for high school and above): http://netlogoweb.org/launch#http://netlogoweb.org/assets/modelslib/Sample%20Models/Biology/HIV.nlogo
For educators and students (grade 3 to adult): Paul Smaldino of the University of California, Merced, has shared a model of COVID-19 pandemic which predicts the spread according to user-adjustable variables like how contagious, social distance, and recovery rate. From the link below, the model can be run in a web browser or can be downloaded to run in the Windows or Mac NetLogo application: http://modelingcommons.org/browse/one_model/6224#model_tabs_browse_info.
High school or university students can modify the code and display of the model to better understand the exponential and emergent properties of a virus outbreak.
Johns Hopkins University is a research center for studying the spread and treatment of virus outbreaks. Here is their description of how a model or simulation can predict the likely spread of a virus so that action can be taken to limit its range or its damage. The predictions are shown visually as static graphs: https://systems.jhu.edu/research/public-health/ncov-model-2/.
The current infection range and summary of the virus spread are graphically shown and continuously updated at this Johns Hopkins page (the most authoritative source of this information): https://coronavirus.jhu.edu/map.html
Why Must We Act Before We See Sickness?
Here’s a page devoted to helping leaders understand the need to act early before the impact of a virus outbreak is widely felt. By the time citizens and many leaders see a health emergency, it’s probably too late. More good graphs and clear explanations. Suitable for high school and above: https://medium.com/@tomaspueyo/coronavirus-act-today-or-people-will-die-f4d3d9cd99ca
For students grade 5-8: What is a virus and how does it replicate and cause disease? A National Geographic explanation with diagrams. https://www.nationalgeographic.org/encyclopedia/viruses/