By Nicole Soussana
When it comes to the novel coronavirus, it seems as though every person you speak to or every news source you turn to has a different theory. With contrasting explanations, many questions can arise. Is it possible to become reinfected or not? Are organs outside of the lungs affected? Why do some people fall deathly ill, while others don’t realize the virus has invaded their bodies? The truth of the matter is that any answers you find to these questions are not precise. There hasn’t been enough time for scientists to state anything definitively. What we can do, however, is study, research, and present intellectually stimulating and plausible explanations.
A typical explanation as to why there exists asymptomatic victims of COVID-19 is that they have a stronger immune system than those who present symptoms. This theory provides an explanation as to why the majority of asymptomatic individuals are children or young adults (under the age of 20). However, some scientists have presented the idea that this phenomenon is not solely explained by immunity but rather in conjunction with disease tolerance.
Disease tolerance is a mechanism which keeps our bodies healthy without directly attacking a pathogen or invader. Disease resistance, on the other hand, aims to kill the pathogen or inhibit its ability to grow and spread. The immune system is an example of the latter. With disease tolerance, there is an internal adjustment that adapts the body for the infection without directly targeting the pathogen. This can be by diminishing the reaction a pathogen causes or by pacifying the pathogen in some way. The outcome? An infected individual does not feel ill. Scientists have seen tolerance responses in plants, and have only recently discovered that animals possess it as well.
An example of disease tolerance that can be compared to the coronavirus is tuberculosis (TB). Research has shown that 90% of individuals with TB don’t fall ill. The TB pathogen has a tendency to stick around for quite some time in the body, increasing immune response, and leading to the chronic inflammatory disease. The ability for a pathogenic disease, such as TB, to live symbiotically in the human body is an example of tolerance. Individuals who present pathogen tolerance, in TB cases, utilize macrophages to suppress inflammation. This mechanism subdues inflammation to a ‘sweet spot’ where the immune system can fight the pathogen, while lasting tissue damage is prevented. Studies have similarly shown that asymptomatic individuals with the novel coronavirus present a weaker immune response compared to those who fell ill, meaning less inflammation. If healthy individuals carrying the coronavirus are not displaying a strong immune response as we would have assumed, this points to there being an additional process outside of the immune system at play in protecting the body from the virus.
Another example of studying disease tolerance sheds light on its rewards. A group researching disease tolerance in mice introduced them to a diarrhea-causing infection. It was found that the mice either died or were completely healthy because they used iron stores to satisfy the bacteria. Iron was then used as a treatment and resulted in 100% success rate of surviving mice.
It is clear from the above examples, that when there are cases of individuals who seem to be able to fight off a pathogen naturally, it may be worthwhile to study those systems. A solution to fighting off a disease may not be the actual battle which ends in killing a pathogen, but rather focuses on maintaining health. While this area of study is fairly new and there is no concrete evidence that it occurs in asymptomatic individuals of COVID-19, it does have future implications on the way we approach a scary pathogen. Maybe ‘attack’ isn’t always the solution.