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How are fire, frogs, and COVID-19 related?

Analogy for COVID-19 spread

When conditions are right, fire quickly spreads from a tiny spark to a roaring fire. Dry wood, lots of oxygen or wind, and kindling such as dried grass can take a spark from a well contained campfire or lit cigarette to a roaring forest fire. Similarly, when the conditions are right, the spread of COVID-19 can quickly rise from one case to many. The conditions leading to a “forest fire of COVID” include a large number of susceptible people (dry wood/kindling), a person with COVID who can spread the disease to others (spark), and the proximity of the spark to the dry kindling. If a spark lands on a blacktop road instead of the dry kindling next to the road, the spark will die out before starting a forest fire. When a COVID-19 positive or exposed person quarantines until they are no longer infectious, they are extinguishing the spark before it lights more fires. If the spark is not extinguished and a fire starts, isolating the fire from dry wood by digging ditches or using water can slow or stop the spread of the fire. Similarly, if an outbreak of COVID-19 occurs, using facemasks and social distancing can slow the spread of the virus from person to person. Sparks can still jump ditches if the fire is hot enough, but the physical barrier will slow the spread of the fire so that it is easier to fight. If the fire is out of control, the forest will burn. Some animals and plants/trees will die from the fire. After the fire has burned up all of the dry tinder, the grass and plants begin to grow again and the animals begin to return. Until more dry material is present to burn, sparks will not ignite another large fire. Once COVID-19 has infected all the susceptible people, the dry tinder will be used up until more dry material exists to burn. More “dry wood” with COVID may happen from the mutation of the virus leading to reinfection or the loss of immunity from the host. The risk and speed of more “dry wood” is currently a COVID unknown. We do not yet know how likely or widespread these possibilities are. With fire, the ideal situation is that the spark is isolated and extinguished before starting a forest fire. Once the fire is started, it is wise to fight the COVID fire with the tools available, social distancing and facemasks. If these tools are not used correctly or effectively, the fire may burn through the forest leaving destruction behind it. After the fire is over, the forest rebuilds itself again because some life is left after the fire. With COVID-19, >90% of people will most likely still be alive after the worst of the forest fire.

Now for a moment, envision that COVID-19 is the frog pictured above. Now grandma living in the nursing home hates frogs. If she sees a frog, she will have a heart attack and die. So will her neighbor on one side, but not the neighbor on the other (I know, this is a “little” overdramatic, but follow me for a minute). This frog was just living its lifestyle and laid many eggs in a pond across the ocean. Grandma wasn’t worried because there was an ocean between her and the frogs. She barely knew that the frog existed. The frog was not malicious because it was simply living its life. These eggs turned into tadpoles and then into frogs. A few of the frogs climbed into a picnic basket which happened to end up on a plane traveling to the country where grandma lived. They quietly hopped out and found their way into a nice quiet stream where they laid more eggs. These turned into many more frogs because the water was warm, and the food was plenteous. Grandma started to get worried because the frogs were closer to where she lived now. She really did not want to see a frog. As the frogs multiplied and increased in number, they arrived at the pond outside where grandma lived. Once the frogs arrived, people decided that it was time to put in place measures to prevent grandma from seeing a frog. So they quarantined all the frogs they could find. Unfortunately, the frogs had already laid eggs which quickly turned into tadpoles and more frogs. Now there were frogs everywhere. Barriers were set up around the pond to keep the frogs away from the front door of the nursing home. Unfortunately, the frogs could climb so some of them escaped over the edge of the barrier. Staff were instructed to wear clothes without pockets to prevent bringing the pesky frogs into the nursing home. Some of the staff laughed, “I am not afraid of a little tree frog, why should I suffer the inconvenience of no pockets? The frog won’t hurt me.” Therefore a few of the staff sewed some of their pockets shut but didn’t sew all of them. Eventually one of the frogs entered the nursing home in the open pocket of a staff member. It decided to lay eggs in the activity room fish tank. Soon there were frogs everywhere. Isolating the residents in rooms slowed the spread of frogs. Eventually, the frogs learned to crawl through the air ducts from room to room until most of the residents had seen a frog. Those susceptible to frog sighting heart attacks succumbed to the frogs. Even a few of the staff succumbed to sighting too many frogs.

In this scenario, the approach to keeping the frogs away from grandma is multi-step and involves physical barriers and cooperation from everyone. Additionally, the fewer the number of frogs, the lower the threat of grandma seeing a frog. If the first frog is caught before it lays eggs, then the whole scenario would have been avoided. This analogy applies on a local scale and is scalable to larger situations. If a COVID-19 case is isolated before “laying eggs” aka infecting other people, the dramatic increase in cases can be avoided. The higher the number of cases, the harder it is to keep the infection out of places with people susceptible to the infection. Physical barriers such as face masks and social distancing slow the rate of infection, not completely stop it. Additionally, it only takes one infectious person to start an outbreak. When someone decides to take risks because “I don’t mind frogs, and I won’t get hurt,” they become the door by which a frog enters a place that it should not be. COVID-19, like frogs, may climb walls and travel through air vents in poorly ventilated homes with residents rooms in close proximity resulting in the uncontrolled forest fire once the frog enters.


Nursing home residents are one of the highest risk groups for COVID-19.

Taiwan is an example where COVID transmission was stopped early before the “forest fire” was started.

Facemasks help to prevent the spread of COVID. See additional annotations at

Social distancing has helped countries control the coronavirus outbreaks.

COVID-19 case fatality rate is ~3–5%. Based on the case fatality rate, >90% of people survive infection.

Travel of COVID through air vents is currently a hypothesis. Probable spread by fecal aerosols is documented. The role of air conditioning in the spread of COVID is explored on WebMD. Scientific discussion about COVID aerosol generation is ongoing with evidence pointing to the possibility of aerosol spread but not conclusively proving it.

Special thanks to Brad Eland for the frog analogy idea.

Frog and tadpole pictures credit: Michelle Gerst, Ph.D.

Forest fire credits: <a href=”">Good Free Photos</a>



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