Today marks the day where I start another series on this blog called decanting diseases. For this series, I will focus on various diseases and try to explain them so that we understand what the disease does and how to protect yourself from the disease. The series will start with the overview of one of the most common cause of pandemic: influenza, or the flu for short.

Influenza is a disease caused by the virus accurately called influenza virus. The virus is propagated through many means: human contact, droplets in the air, sneezing, etc… The virus exists in four categories: A, B, C, and D, though today we will only focus on influenza A, being the most common. The influenza A virus in itself is quite complex, but its main components are its RNA segment, which allows it to replicate inside cells, and two proteins called Hemagglutinin (H) and Neuraminidase (N), which help the virus to enter the cell. Many variation of the H and N protein exist, and that’s why we also categorize influenza A with the combination of H and N. For instance, the avian flu was an influenza A H5N1, while the Spanish flu was H1N1. The virus will enter the respiratory tract and infect these cells to replicate itself. In healthy individuals, the infection is self-limiting, meaning that the virus will be removed from the system eventually. However, people with respiratory or immune problems may have more problem [source / source / source / source].

Flu symptoms are quite severe and include extreme fatigue, headaches, chest pains, coughing, and high fever. Even in healthy individuals, these symptoms may last up to three weeks. People at risk may have complications including pneumonia and respiratory failure, which may be fatal. The treatment for influenza is quite simple: in healthy individuals, ibuprofen or acetaminophen can reduce the symptoms a bit but no antiviral is needed. In case of outbreak or severe cases, many antiviral, all of which prevent the N protein from working, will help fight the virus. In any case, aspirin should never be given in case of flu in children. For reason that are still poorly understood, the reaction between influenza virus and aspirin will increase the risk of a disease called Reye Syndrome. This syndrome is an encephalopathy, which means that the brain is infected by the virus. This is extremely dangerous, and primary symptoms are excessive vomiting and change in mental state, all caused by brain swelling. This can lead to complications such as seizure or unresponsiveness. There are no cure and treatment will only aim to alleviate the symptoms. As a general rule, if a child has symptoms resembling the flu, never give them aspirin or any drug containing salicylates. Finally, flu outbreaks can be greatly reduced by taking the yearly flu shots, which creates antibodies against the N and P proteins that are the most likely to appear during winter [source / source / source / source].

What makes influenza scary is its great ability to mutate. Influenza A’s genetic material can easily be modified. This is called an antigenic drift. This difference is small enough, but can render the virus less detectable by the immune system. These changes happen extremely often and there are the main reason why we don’t have a definitive vaccine against influenza. We have to get shots every year because we know which virus will appear this year, but the next year entirely new influenza viruses will appear and the previous shot becomes obsolete. Scarier than the drift, influenza viruses are able to do antigenic shifts. The virus is able to infect many different species, including pigs, horses, and birds, and if a human influenza virus enters a bird, it can « exchange » its genetic material with bird influenza viruses. This causes an entirely new influenza viruses that has never been seen before, with N and H proteins that can not only enter our body, but cannot be stopped by our immune system. It happened in the early 2000s during the avian flu pandemic, where the H5N1 virus had bird-like material, making it harder to fight. The worse case was in 1918, during the Spanish flu pandemic. This specific H1N1 virus was entirely new to humans, rendering it virtually immune to our protection. It was so strong that it was most dangerous for people in their 20s, which is normally the population that is the least likely to suffer from the flu. To this day, we still don’t know why young people were so strongly affected, and why it had such a high death rate, which is still the highest any flu pandemic had. Fortunately for us, there has never been a virus as strong as this one, and it mutated to be less efficient. Furthermore, many scientist say that it is unlikely for the virus to have such a strong effect nowadays, because we have a stronger immune system and less respiratory problems overall. Although, the swine flu pandemic a few years ago did scare the scientific community, seeing as it was also a H1N1 virus. Fortunately, it wasn’t as strong as the 1918 one. A few years ago, scientists managed to reconstruct the 1918 H1N1 virus, and we hope to study it in order to understand the disease evolution to better fight it [Source / source / source / source / source].