When the weather is getting colder, the cold and flu season starts. Many people don’t worry much about catching a cold, because it is the flu that can get you really sick and feel miserable for days. The typical symptoms of flu: fever, chills, cough, headaches, muscle aches, sore throat, and fatigue start abruptly. No matter what you do, you will feel head-to-toe distress for a few days.
Why is that? Why does the flu make you feel so bad?
Believe it or not, it is your body’s response more than the virus itself the biggest culprit.
Your body’s response to a virus
The reason you feel so sick and have symptoms is that the immune system’s main role is to fight and eliminate the viruses such as influenza.
If the immune system had past experience with an influenza virus, it was already trained. It recognizes the virus and can quickly send antibodies out to fight the infection. But when a new, different strain of influenza circulates in the environment, as it happened with the H3N2 strain, the immune system starts to work hard. It floods the body with certain chemicals called cytokines. Many of these cytokines promote inflammation in an attempt to attack the viral particles and prevent their replication. These inflammatory cytokines are released into the bloodstream, and from the blood spread throughout the body in various organs and tissues. When these inflammatory cells reach the muscles and the joints, they cause muscle aches and pains. When they enter the airways, they cause a runny stuffy nose, coughing, sneezing, and excess mucus.
Special cytokines are also responsible for raising the body temperature, causing fever. Fever helps reduce viral growth, as influenza viruses multiply best at lower temperatures.
The interferons are also a family of cytokines that fight viruses through multiple mechanisms. They alert the immune system that a new virus is infecting the body’s cells. They also have direct antiviral effects and boost the immune response to better fight the infection. However, in this process, interferons are also in part responsible for experiencing headaches during the flu. Another reason why headaches develop is that the fever leads to dehydration. Dehydration also promotes dilation of the blood vessels in the brain, leading to headaches.
In severe cases of flu and other viral infections, these cytokines create excess inflammation so-called a cytokine storm. In the case of a cytokine storm syndrome, certain pro-inflammatory cytokines are found in much higher than normal amounts in the blood. A person with this condition experiences very severe symptoms of flu, along with shortness of breath, rapid breathing, confusion, lethargy, seizures, or swelling of the legs. The cytokine storm syndrome is life-threatening as it causes acute respiratory failure, organ damage and can lead to death.
It is important to know that not all cytokines cause inflammation and can be blamed for causing symptoms. Other cytokines work behind the scenes, supporting other immune cells to fight the virus or help produce antibodies. There are also plenty of cytokines that have anti-inflammatory effects.
The influenza viruses have their unique characteristics
The influenza virus can directly attack vital organs such as the heart or lungs, disrupting and damaging their normal structure. This process explains in part, why flu can lead to inflammation of the heart or pneumonia. However, the most severe forms of flu and deaths are caused by cytokine storms and complications of flu (i.e. secondary bacterial infections), rather than direct tissue damage caused by the virus.
Why is the flu more severe than a common cold? The common cold affects us more often than the flu. The average person will experience 200 episodes of cold, but less than 20 episodes of flu during the entire lifetime. The immune system recognizes the cold viruses easier and fights them more effectively. Although viruses responsible for the common cold mutate often, having exposure to past strains helps the body to cope with new ones.
Influenza viruses, however, mutate in a significant way. This is one of the main reasons why flu vaccines have to be changed yearly, to include potential strains that will circulate during a certain year. New influenza strains can evolve and become unrecognized by the immune system. The subtype of influenza strains also makes a difference. The most dangerous one is the type A influenza strains. This type causes more severe symptoms and is responsible for pandemics. The deadly Spanish flu pandemic from 1918 and the swine flu from the 2009 outbreak were both influenzas A strains.
There are quite a few things that can save you a lot of misery and recover quickly. Get plenty of rest, eat light, have hot teas and soups throughout the day, avoid stress and avoid overtraining. Check out this article for some tips and home remedies, or this one about over-the-counter cold and flu medicine.