What causes flu

What Causes the Flu?

The influenza virus is the culprit behind the illness commonly known as the flu. It's a highly contagious respiratory illness that can lead to mild to severe sickness, and at times can lead to death. Unlike the common cold, which is caused by a variety of viruses, the flu is specifically caused by influenza viruses.

Understanding Influenza Viruses

There are four main types of influenza viruses: A, B, C, and D. However, only types A and B are responsible for the seasonal flu epidemics that affect humans each year. Influenza C viruses usually cause mild respiratory illness and don't cause epidemics. Influenza D viruses primarily affect cattle and are not known to infect or cause serious illness in humans.

Influenza A Viruses

Influenza A viruses are further classified into subtypes based on two proteins on their surface: hemagglutinin (H) and neuraminidase (N). There are many different subtypes, such as H1N1 and H3N2, which are known to infect humans and cause seasonal flu. These viruses are also responsible for flu pandemics, which are global outbreaks that occur when a new influenza virus emerges and spreads easily among people.

Influenza B Viruses

Influenza B viruses circulate among humans and are also a common cause of seasonal flu. Unlike influenza A, influenza B viruses are not classified into subtypes. However, they are divided into lineages, with B/Victoria and B/Yamagata being the two most prevalent lineages that cause illness in humans.

How the Flu Spreads

Influenza viruses are spread from person to person primarily through respiratory droplets. When an infected person coughs, sneezes, or talks, tiny droplets containing the virus are released into the air. These droplets can then be inhaled by people nearby, leading to infection. This is why crowded places can be breeding grounds for the flu, especially during flu season.

Droplet Transmission

This is the most common way the flu spreads. If you are within about six feet of someone who is infected, you can inhale these droplets directly into your lungs. This highlights the importance of maintaining distance from sick individuals and practicing good respiratory etiquette, such as covering your mouth and nose when coughing or sneezing.

Surface Transmission (Fomites)

Influenza viruses can also survive for a period on surfaces like doorknobs, phones, keyboards, and tabletops. If a person touches a contaminated surface and then touches their own eyes, nose, or mouth, they can become infected. This is why frequent handwashing and disinfecting frequently touched surfaces are crucial preventive measures against the flu.

Factors Influencing Flu Transmission

Several factors contribute to the spread of influenza:

• Seasonality: Flu viruses tend to spread more easily in cooler months, typically in the fall and winter. While the exact reasons are still being researched, theories include people spending more time indoors in close proximity, lower humidity levels that allow viruses to travel further, and potential effects of cold air on the immune system.
• Viral Characteristics: Influenza viruses are known for their ability to change rapidly through a process called antigenic drift and, less frequently, antigenic shift. Antigenic drift involves small changes in the genes of influenza viruses that happen continually over time. These gradual changes allow the virus to evade immunity built up from previous infections or vaccinations. Antigenic shift is a more abrupt, major change in influenza A viruses that can lead to pandemics.
• Human Behavior: Increased travel, social gatherings, and close contact in schools and workplaces can all facilitate the rapid spread of the flu virus.

Preventing the Flu

While understanding the causes of the flu is important, knowing how to prevent it is equally vital. The most effective way to prevent the flu is to get an annual flu vaccination. The vaccine is updated each year to protect against the influenza viruses that are expected to be most common during the upcoming season. In addition to vaccination, practicing good hygiene, such as frequent handwashing, avoiding close contact with sick people, and covering coughs and sneezes, can significantly reduce the risk of infection.