We have already discussed that the influenza virus has more than the two popular types: influenza A and influenza B virus. But it is a common fact that these two types of influenza viruses are the ones that cause the seasonal epidemics, which means that it concerns the public health in a constant manner. Today we are going to take a closer, much closer look to influenza A and influenza B viruses.
Let’s start with influenza A viruses. Influenza A viruses are divided into subtypes according to their glycoproteins. Glycoproteins are the surface membrane proteins that are
Influenza A viruses contain hemagglutinin (H) and neuraminidase (N) as their surface proteins. There are 18 different hemagglutinin subtypes and 11 different neuraminidase subtypes. Current subtypes include A(H1N1) and A(H3N2) which refer to different glycoproteins on the viruses.
To understand a little bit more about the taxonomy, which means the classification of the influenza A and influenza B viruses here is a diagram by CDC:
As you can see, the classifications are made based on the viruses’ HA gene sequence similarity. It does not necessarily mean that they are antigenically different (antigens are some of the glycoproteins such as hemagglutinin and neuraminidase). To expand this, Note that clades and sub-clades that are genetically different from others are not necessarily viruses from a specific clade or sub-clade may not have changes that impact host immunity in comparison to other clades or sub-clades.
Currently circulating influenza A(H1N1) viruses are related to the pandemic 2009 H1N1 virus that emerged in the spring of 2009 and caused a flu pandemic. This virus, called “2009 H1N1,” has continued to circulate seasonally since then. These H1N1 viruses have undergone relatively small genetic changes and changes to their antigenic properties (i.e., the properties of the virus that affect immunity) over time.
An image showing the summary of internationally accepted naming convention for influenza viruses, which was accepted by WHO in 1979.
Influenza B viruses are not divided into subtypes like influenza A viruses, but instead are further classified into two lineages: B/Yamagata and B/Victoria. Similar to influenza A viruses, influenza B viruses can then be further classified into specific clades and sub-clades. Influenza B viruses generally change more slowly in terms of their genetic and antigenic properties than influenza A viruses. Even though the co-circulation periods depend on the geographical location it can be generalized that the influenza A viruses circulate faster than the influenza B viruses.
For those who are interested in the topic, we are leaving further materials’ links under the references. We hope you enjoy the lobbies of the influenza virus genomes. Also make sure to check FluAI for your personal health assistance, circulation of these viruses should not leave us unguarded.
Types of Influenza Viruses. Centers for Disease Control and Prevention. (2020). Retrieved 10 October 2020, from https://www.cdc.gov/flu/about/viruses/types.htm.
Cell.com. (2020). Retrieved 10 October 2020, from https://www.cell.com/action/showPdf?pii=S0966-842X%2818%2930131-8.
American Society for Microbiology. Influenza Viruses by James McSharry, PhD. (2020). Retrieved 12 October 2020, from https://www.youtube.com/watch?v=gAmfI5T7XOM.
PM & Clinical Team