Influenza continues to be a major public health concern.The World Health Organization (WHO) estimates that in a typical year, 10 to 20 percent of the world’s population is infected with influenza, resulting in 3,000,000 to 5,000,000 severe illnesses and 250,000 to 500,000 deaths (World Health Organization, 1999). In the United States, there are tens of thousands of deaths each year and the problem will increase due to the aging of the population and the susceptibility of the elderly. Influenza, generally referred to as ‘flu,’ is an contagious illness caused by an influenza virus. Some might heard about swine flu, bird flu, H1N1 or H3N2. The flu is a viral illnes that can range from mild to severe. The most frequent symptoms include: high fever, runny nose, sore throat, muscle and joint pain, fatigue, coughing and feeling exhausted. Influenza virus usually transmitted through coughing or sneezing. The droplets formed by coughing and sneezing that contain the influenza viruses can be spread through the air or just by touching surfaces that contaminated with the virus and then the person touch their faces, nose and eyes. This is how influenza virus will infect the individual person.
There are four types of flu viruses that can infect human which are type A,B,C and D. These viruses are divided into subtypes with some infecting humans and others infecting animals such as pigs and birds. These viruses are named after their editor protein spikes called hemagglutinin (H) and neuraminidase (N). Human influenza A and B viruses in the United States cause seasonal illness epidemics (known as the flu season), nearly every winter. Influenza A viruses are the only influenza viruses known to cause flu pandemics, that is to say, global flu outbreak epidemics. A pandemic can occur when a new and very different influenza A virus develops that both infects people and has the potential to effectively spread among people. Influenza type C infections typically cause mild influenza, and are not thought to cause epidemics of human flu. Influenza D viruses primarily affect cattle and are not known to infect or cause disease in humans.
Influenza viruses are constantly changing. They can change in one of two different ways; antigenic shift and antigenic drift. Antigenic drift results from continuous changes which modify the surface proteins of influenza viruses (H and N proteins) until the virus is eventually no longer recognized by the immune system. The changes associated with antigenic drift happen continually over time as the virus replicates. Because these antigens change, people can get influenza infections multiple times over their lifetime. The immune system of the body produces antibodies that recognize and bind to ‘antigenic sites’; areas located on the surface proteins of an influenza virus. Antibodies neutralize the flu viruses by binding to these antigenic sites, which stops them from causing further infection. Due to the constant changes of influenza viruses, antibodies produced by the immune system can not identify and bind to antigenic sites. This will lead to further infection.
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Based on the theory about antigenic shift and antigenic drift, influenza strains are constantly mutating. Antigenic drift is referred to a small change of the influenza strains while a major change is called antigenic shift. Over years, these minor changes in the genes of influenza viruses result in a new strain that is not recognized by the immune system. In short, the antibodies created last year are unable to fight against this new version of virus. That is why some people can get sick from the flu even though they have had it before. According to scientists at Fred Hutchinson Cancer Research Center also find that a single mutation in the flu virus can sometimes give it the power to evade our antibody immunity to about 90%, but no others. This finding can help explain why individuals differ so greatly with respect to influenza virus susceptibility. There might be person-to-person variation in how influenza virus evolves to escape human immunity in order to fight against influenza virus or in another word, the same virus strain might have different effects on different people (Jesse, 2019).
But why some years people experience no disease even they get infected by the same strain virus with people that get flu in the same year? This can be explained by the lifestyle of people and their daily dietary intake which may cause variation in the function of the immune system among individuals. Theoretically, healthy immune system warriors need good and regular nourishment. Scientists have long recognized that malnourished people who usually live in poverty are more vulnerable to infectious diseases. For example, people that take enough micronutrient such as zinc, iron, copper, folic acid, and vitamins A, B6, C, and E will keep their immune system strong. So, this will decrease the tendency for these people to get disease like flu. As we know that nowadays, many people have awareness on consumption of dietary supplements such as vitamin C. So, what is the importance of taking vitamin C in our daily diet? According to Anitra C. Carr (2017), vitamin C is a powerful antioxidant having ability to contribute to immune defense by supporting various cellular functions of both the innate and adaptive immune system. Even though the role of vitamin C in lymphocytes is unclear but it had been shown that vitamin C can enhance the differentiation and proliferation of B- and T-cells due to its gene regulating effects. In short, vitamin C really helps improve our immune system and reduce the risk of getting flu.
Besides that, scientifically, stress can weaken our immune systems. In a stress condition, our innate immune system and cell mediated immune system will be affected. Stress can effect our brain undergoes a process that elevate Corticotrophin Releasing Hormone (CRH) . It will suppress immune system by reducing the function of NK cells and also T cell. So, our body prone to get infectious disease such as flu as the development of NK cells and T-cell are very important in order to fight microbes. Stress can also have indirect impact on the immune system by practising unhealthy lifestyle. It happens when a person drink alcohol and smoking as ways for them to relieve stress. This unhealthy behaviour will affect our immune system.
Human influenza or better known as the ‘flu’ is a common infectious disease that can easily transmit from one person to another by tiny little droplets of mucus through the air. There are 4 types of this virus which are type A, B, C and D but there are two main types of influenza (flu) virus that have been focused here; Types A and B. Our main concern on influenza virus features are the surface proteins hemagglutinin (H) and neuraminidase (N) because the changes of these antigenic structures can be related to antigenic shift and antigenic drift. These two ways of changing influenza viruses results in making a new strain of virus hence, make the virus unrecognized by our immune system. That is the reason why some people get infected by this flu virus many times. But, not all people can be infected by this virus as this also depends on their immune system activity. Good or bad lifestyle, dietary supplements and stress levels can be one of the factors that may affect the immune system conditions and thus, it will affect the strength of our immune system to fight against the invasive viruses. All in all, the best way to prevent the flu is to get yearly influenza vaccine.
- Anitra C. Carr & Silvia Maggini. (2017, November 3). Vitamin C and Immune Function. Retrieved March 25, 2020, from https://www.mdpi.com/2072-6643/9/11/1211.
- Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases (NCIRD). (2019, July 10). Understanding Influenza Viruses. Retrieved March 22, 2020 from https://www.cdc.gov/flu/about/viruses/index.htm.
- Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases (NCIRD). (2019, October 15). How the Flu Virus Can Change: “Drift” and “Shift”. Retrieved March 22, 2020 from https://www.cdc.gov/flu/about/viruses/change.htm.
- Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases (NCIRD). (2019, October 15). Antigenic Characterization. Retrieved March 23, 2020 from https://www.cdc.gov/flu/about/professionals/antigenic.htm.
- Saul McLeod. (2010). Stress, Illness and the Immune System. Retrieved March 25, 2020, from https://www.simplypsychology.org/stress-immune.html.
- Suzanne L. Epstein. (2003). Control of Influenza Virus Infection by Immunity to Conserved Viral Features. Retrieved March 21, 2020, from https://www.ncbi.nlm.nih.gov/books/NBK22159/.