When it's cold season, you'd be smart to get a flu shot. This lesson will delve into influenza pandemics, epidemics, the bird flu, the swine flu, hemagglutinin, neuraminidase, and much more as we explore the members of the Orthomyxoviridae virus family.
The Orthomyxoviridae Virus Family
This lesson pertains to everyone. And I mean everyone. There likely isn't a single person in the world that hasn't at one point in their life been infected with at least one of the viruses in the Orthomyxoviridae family. That's because this is the family of viruses that causes one of the most famous conditions humans experience, one that has, at times, killed millions of people all over the world. We'll get into that and more as we take a look at the Orthomyxoviridae structure, methods of transmission and its famous diseases.
Orthomyxoviridae Structure and Transmission
The viruses in this family are enveloped and have a helical capsid that encloses a single-stranded negative sense RNA genome, although it's important to note that these viruses may sometimes appear as a sphere. The envelope has two important structures. The first is called hemagglutinin, commonly abbreviated as HA. With respect to viruses in this family, hemagglutinin is a glycoprotein that helps a virus recognize and enter its host and serves as a target for antibodies that are trying to kill the virus.
Basically, this glycoprotein helps the virus stick to the cell it wants to attack, or allows the immune system's antibodies to stick to the virus the immune system wants to kill. Since the word 'agglutination,' in hemagglutinin, means to attach, or stick to something, you'll always remember what hemagglutinin in viruses is for: It helps the virus to stick to a cell.
The second important structure is called neuraminidase, commonly abbreviated as NA. This is an enzyme that allows a virus to be released from its host. Keep these two abbreviations, HA and NA, in mind for the near future. While the viruses in this family can be spread through more than one route, when it comes to the main viruses that affect humans, without a doubt, the most important route of transmission is the respiratory route, such as when someone sneezes or coughs and another person inhales these secretions, only to be infected themselves.
Influenza, Flu, Swine and Pandemics
The most famous disease caused by the viruses in this family is called influenza, the more technical term for the flu. I think that I don't really have to list the symptoms most people get from the flu since you've almost certainly had it yourself, but just in case you somehow lucked out, the flu typically causes a fever, muscle aches, fatigue, coughing, sneezing, congestion and an overall really miserable time.
Most of the time, people recover from the flu without a hitch. However, this wasn't the case in something known as the 1918 flu pandemic, which is also known as the 'Spanish flu.' Just in case you weren't aware, a pandemic is an epidemic that occurs over a wide area, such as multiple continents or the entire world, while an epidemic is an outbreak of disease that affects a disproportionately higher number of individuals than normal.
The Spanish flu was one such pandemic and ended up affecting half a billion people and killing upwards of 100 million people around the world in a three-year span. The specific influenza virus that caused this pandemic is known as H1N1, and a slightly newer version of this virus caused the 2009 flu pandemic, also known as the swine flu.
Why You Need a Flu Shot Every Year
Hopefully, you recognized the HA and the NA in H1N1. The letters are there for a reason. The main species of virus involved in the flu is the influenza A virus that is classified based on the type of hemagglutinin or neuraminidase subtype that this virus genetically encodes for.
The problem is that flu viruses love to constantly undergo something known as antigenic drift and antigenic shift. The specifics of how this occurs are covered in another lesson. But basically, these mechanisms either cause slight variations in the HA and NA proteins, in the case of antigenic drift, or massive variations in the HA and NA proteins, in the case of antigenic shift.
The variations in the HA and NA are there for a reason: They help the virus avoid your immune system, thereby allowing it to spread among the population. Remember, your immune system can only respond to something it has been exposed to before. Since antigenic shift and drift produce new strains your body hasn't been exposed to before, you're more likely to get sick when infected with the new viral strain, unless you've already been vaccinated against it.
For example, changes in influenza A have created subtypes called H5N1 and the newer H7N9, which are viruses that cause something known as avian influenza, which is more commonly referred to as the 'bird flu.' These viral strains are typically only found in birds. However, humans who have come into contact with live or dead birds carrying this virus have been known to become infected. A far greater amount of people die if they contract the avian flu than if they get the seasonal flu that most of us fall victim to.
This is mainly because little pre-existing immunity to these strains exists, compared to strains associated with the seasonal flu, but also because bird flu has been shown to cause a lot more inflammation in the human body, which can result in higher mortality rates. So, the reason a yearly flu shot is recommended is so that the shot can boost your immune system for newly developed strains for which you may have little or no immunity to.
For our summary, recall that antigenic drift and shift affect two proteins located on the influenza virus. The first is called hemagglutinin, which is a glycoprotein that helps a virus recognize and enter its host and serves as a target for antibodies that are trying to kill the virus off. The second is called neuraminidase, which is an enzyme that allows a virus to be released from its host.
The most famous disease caused by the viruses in the Orthomyxoviridae family is called influenza, which is the more technical term for the flu. Most of the time, people recover from the flu without a hitch. However, this wasn't the case in something known as the 1918 flu pandemic, which is also known as the 'Spanish flu.'
Just in case you weren't aware, a pandemic is an epidemic that occurs over a wide area, such as multiple continents or the entire world, while an epidemic is an outbreak of disease that affects a disproportionately higher number of individuals than normal. The specific influenza virus that caused the pandemic of 1918 is known as H1N1, and a slightly newer version of this virus caused the 2009 flu pandemic, also known as the 'swine flu.' Finally, influenza A has many other subtypes, such as H5N1 and the newer H7N9, which are viruses that cause something known as avian influenza, which is more commonly referred to as the 'bird flu.'
After you've completed this lesson, you'll be able to:
- Detail the structure of the Orthomyxoviridae virus family
- Emphasize the importance of hemagglutinin and neuraminidase
- Understand the meanings of antigenic drift and antigenic shift
- Recognize the necessity of flu shots
- Relate the primary diseases caused by Orthomyxoviridae
- Report on the 1918 H1N1 pandemic and the 2009 avian influenza pandemic