Fever. Pain in the limbs. Irritability. Drowsiness. Loss of appetite. Congratulations, you have the flu! Well… actually, not really “congratulations.” The flu is annoying, incredibly inconvenient, dangerous, and slow to leave, but at the same time it raises a question: Why must we suffer a biological civil war every time it appears? As if that weren’t enough, the chaos is not limited to flu cases, and the vast majority of infections generate a similar reaction. The answer goes beyond the pathogen itself...
“A week of rest, plenty of fluids, and no antibiotics”. How many times have we heard those words from a doctor after detecting the flu? The goal is none other than to help the immune system concentrate its firepower on the bug in question and optimize recovery time, but it’s one thing to say it and another to do it. The truth is that we don’t have time for the flu, and that always gives it a rematch, which can lead to potentially dangerous situations (not resting, self-medication, etc.).
Meanwhile, besides spitting demons in all directions, we feel daggers in our head, arms, and legs, we run a fever, sleep hits us like an anvil, and hunger takes a vacation. The question… is why.
Malaise and illness
Believe it or not, the responsible party is not the pathogen itself. As soon as it is detected in the system, macrophages rush into the fray and begin their attack, destroying the virus and infected cells alike. Then, the macrophages begin producing proteins called cytokines, whose role is to recruit and manage more cells to concentrate their attack, and they include pro-inflammatory and pyrogenic actions (fever).
In the best case, the infection is neutralized before we feel its consequences, but if the virus spreads to the rest of the body, the immune system must operate on a large scale and coordinate efforts with the brain. The additional production of cytokines stimulates the vagus nerve, transmitting information to the brainstem, where pain is processed.
Then, the cytokines travel to the hypothalamus, our “control” for temperature, hunger, thirst, and sleep. In turn, the hypothalamus produces prostaglandin E2, a mediator of the febrile response. The hypothalamus orders muscle contraction, induces sleep, and any idea of eating or drinking goes down the drain.
So, what is the definitive plan? What good are fever, nausea, and pain when fighting an infection? Several studies suggest that they assist in recovery. The increase in temperature reduces the presence of bacteria and increases the immune system’s attack power. Sleep is interpreted as a reallocation of energy, channeling more resources toward fighting the infection.
By not ingesting food, the liver accesses much of the iron in the blood, an action that starves the bacteria that need it. The double-edged sword is dehydration. On one hand, it decreases transmission of the pathogen (fewer particles in sneezes and coughs, less vomiting and diarrhea), and on the other, it must be kept in check.
Finally, mood changes and confusion are the result of cytokines and prostaglandin E2 reaching other brain structures (the cortex and the entire limbic system), affecting their proper functioning.
TED-Ed on YouTube: Click here
