Influenza, commonly known as the flu, is an airborne respiratory infection. The causes of influenza are various strains of the influenza virus, which belongs to the family Orthomyxoviridae. These strains are created as the main virus shows high rates of mutations and changes its structure frequently. Humans do not have immunity to the new strains (similar viruses with minor differences) that emerge through such mutations. As a result these recurring processes create pandemics, in which the infection spreads rapidly across continents in a short span of time, causing several deaths and requiring the hospitalization of many people.
Causes Of Influenza – The Influenza Virus
The influenza virus is grouped into 3 types – A, B, and C, based on the protein and nucleic acid composition of the virus. Human infection is caused most frequently by the Influenza A type of virus. There are also reports of infection caused by the type B virus, but infection by the type C virus is rare.
Influenza viruses are RNA viruses because their genetic material is RNA. The virus has two protein spikes termed Haemagglutinin (HA) and Neuraminidase (NA). HA plays a major role in the attachment of the virus to human respiratory cells, while NA influences the progression of the infection. 16 HA and 9 NA have been identified till date.
Based on the nature of the HA and NA spikes, influenza viruses are again grouped into various sub types such as H1N1 (Swine Flu), H3N2 (Seasonal Flu), and H5N1 (Bird Flu).
The Source Of The Infection
Wild aquatic birds such as ducks and shore birds are collectively the primary reservoir of the influenza virus. Such birds shed the virus in their excreta, which then acts as the source of infection.The flu virus may mutate and readily jump to species like domestic poultry or swine. The influenza viruses that infect birds and those that infect humans are both capable of infecting pigs. This leads to the mixing up of both the distinct strains, causing an emergence of a new influenza virus which can spread from pigs to humans. This came true during the 2009 H1N1 pandemic, where the pigs acted as the mixing bowl for influenza virus reassortment (mixing up of genes).
The influenza infection is airborne. The virus is transmitted from one person to another through the air. When an infected individual coughs, sneezes, talks, or spits, the respiratory droplets that carry the virus are exposed to the environment. These viruses then enter the body of another individual through his nose or mouth. Airborne infections can even spread to persons standing up to 6 feet away.
Indirect transmission can also occur in rare cases, when a person’s nose or mouth gets infected by his hands that have already been in contact with contaminated surfaces.
How The Infection Occurs
Once the virus enters a person’s body through his nose, it attaches to the host’s respiratory epithelial cells with the help of the surface protein Haemagglutinin (HA). The virus then travels down the respiratory tract causing much internal damage and finally infects the person’s lungs, leading to pneumonia and bronchitis.
The Life Cycle Of The Influenza Virus Within The Body
Once inside the cells, the influenza virus takes over the host’s body to replicate and produce more viral particles to spread the infection further.
A person infected with influenza sheds the causative virus in his respiratory secretions even before the flu symptoms have manifested. In children, the shedding of the virus can continue for up to 7 days or more.
The Causes Of Influenza – How To Keep The Infection From Spreading
If you’ve been infected with influenza, you should take extra care to ensure that you do not unwittingly spread the infection to others. Here are some precautionary measures you can take:
- Cover your nose and mouth while coughing or sneezing, or wear a mask to cover your nose and mouth at all times during the infection
- Stay away from your workplace and do not attend any public gatherings when you’re down with the flu. If your child has influenza, do not send him to school or out to play with other kids
- Wash your hands vigorously with soap and water or with alcohol based hand rubs.
Influenza can cause serious complications and even turn fatal when not diagnosed and treated on time. For this reason, it’s important for you to protect yourself and your family from the causes of influenza, at least by getting the flu vaccine and maintaining high levels of hygiene and sanitation.