Influenza Type A

Genomics Revolution

Genomics Revolution

Benjamin Blake Erman and Ciza Sadoke

Episode 41: Influenza Virus Type A

Script:

Hello and welcome to Genomics Revolution. Today’s episode is hosted by me, Blake Erman and my partner, Ciza Sadoke, which we’ll hear from later on in the podcast. We are from Brad Goodner’s 2020 Hiram College Genetics course and today we will be focusing on the virus Influenza Type A. This virus causes Influenzae which can give you the symptoms of; a fever, chills, headaches,muscle aches, feeling tired and weak, sneezing, stuffy or runny nose, sore throat and cough (healthdirect, 2018). This disease has been thought to be around in humans for about 6000 years although the first instance of influenza symptoms were recorded around 2400 years ago. Despite this long period of time Influenza wasn’t truly discovered until 1918. This disease was discovered not from the study in humans but through studies of animal diseases by veterinarian J.S. Koen. Koen noticed the close similarities of the disease in pigs that he was working on compared to the then ongoing “Spanish” influenza pandemic of 1918. However, the Spanish influenza pandemic has not been the only influenza type A caused pandemic. According to a review article by Susan Baigent and John McCauley Influenza Type A has caused six pandemics throughout both the 19th and 20th centuries (Baigent, 2003). These pandemics have resulted from the introduction of genes from an animal-derived virus being put into the genetic background of a currently circulating human virus by the process of reassortment (Baigent, 2003). Due to reassortment being a highly developed ability of the disease and the disease causing high mortality throughout time in both humans and animals it is important to understand it to prevent its spread.

It wasn’t until 1933 through the diligent work of researchers Christopher Andrews, Patrick Laidrow, and Wilson Smith that the first human influenza virus was discovered (Kuszewski, 2000). Through their work a vaccine was made and the influenza virus was found to belong to the Orthomyxoviridae family. This family can be divided into two genera, the first includes both influenza A and B viruses while the second the influenza C virus (Kuszewski, 2000). For today, we will be focusing on this first genera, the one including influenza A. The type A virus has many subtypes that are distinguished by the antigenic properties of surface glycoproteins of the virus (Kuszewski, 2000). These glycoproteins are haemagglutinin (HA) and neuraminidase (NA) and they have 15 and nine different types respectively (Kuszewski, 2000). These multiple different types add to influenza type A’s complexity and is why it is a recurring disease. Most of the pandemics previously mentioned were caused by different compositions of this virus such as H1N1 or H2N2. And now to pass it off to my partner.

Hello my name is Ciza Sadoke and I will be finishing the rest of today’s podcast. Picking up where my partner left off, Influenza type A’s genome consists of eight negative sense single-stranded RNA molecules and they can range in size from 890 nucleotides to 2341 nucleotides (McCauley, 1983). These eight RNA molecules total up to about 14,000 nucleotides in length (Virology, 2009) and encode for eleven proteins (Samji, 2009). There are two ways that the influenza type A virus can change, and these changes are continuously happening at random in the genome. One of the ways the influenza virus can change is through Antigenic drift. These are small changes in the genes of the influenza virus that can lead to changes in the surface proteins. This means that they get recognized by the immune system and are capable of triggering an immune response. The genetic drift of influenza virus genomic sequences occurs through the combined effects of sequence alterations introduced by a low-fidelity polymerase and the varying selective pressures experienced as the virus migrates through different host environments (Kim, 2018).

The other way the influenza type A virus can change is through antigenic shift. Antigenic shift occurs when there is an abrupt major change in the influenza A virus. This can result in new HA and NA proteins in the influenza viruses that can infect humans. These shifts can result in different influenza A subtypes in humans. One way shift can happen is when an influenza virus from an animal population gains the ability to infect humans. When a virus is produced that can infect human cells and it has new subtypes of these proteins. The people population will now have to little no protection against it, and therefore the virus will be rapidly spread throughout population. This antigenic shift process is responsible for three major influenza pandemics in the 20th century, including the Spanish flu in 1918, which killed 3% of the worlds entire population at the time (Taubenberger,2006). Also, due to the segmented genome of influenza type A, recombination can occur quite frequently and make a form of the virus that populations have no immunity against (McCauley, 1983). Even current human influenza virus vaccines are only protective against currently circulating strains and close variants of the virus (Baigent, 2003). These vaccines contain inactivated mixture of types A and B strains and this would not have been possible without its sequenced genome. This is all that we have time for today. Thank you for listening to today’s episode of Genomics Revolution. We hope you have enjoyed and have a good day!

References:

Baigent, S. J., & Mccauley, J. W. (2003). Influenza type A in humans, mammals and birds: Determinants of virus virulence, host-range and interspecies transmission. BioEssays, 25(7), 657–671. doi: 10.1002/bies.10303

Influenza A (flu). (May 2018). Retrieved April 5, 2020, from https://www.healthdirect.gov.au/influenza-a-flu

Influenza Type A Viruses. (2017, April 19). Retrieved April 5, 2020, from https://www.cdc.gov/flu/avianflu/influenza-a-virus-subtypes.htm

Kim, H., Webster, R., & Webby, R. (2018, March 01). Influenza Virus: Dealing with a Drifting and Shifting Pathogen. Retrieved April 10, 2020, fromhttps://www.liebertpub.com/doi/abs/10.1089/vim.2017.0141?rfr_dat=cr_pub

Kuszewski, K., & Brydak, L. (2000). The epidemiology and history of influenza. Biomedicine & Pharmacotherapy, 54(4), 188–195. doi: 10.1016/s0753-3322(00)89025-3

McCauley, J. W., & Mahy, B. W. J. (1983). Structure and function of the influenza virus genome. Biochemical Journal, 211(2), 281–294. doi: 10.1042/bj2110281

Noronha, J., Liu, M., Squires, R., Pickett, B., Hale, B., Air, G., . . . Scheuermann, R. (2012, May 15). Influenza Virus Sequence Feature Variant Type Analysis: Evidence of a Role for NS1 in Influenza Virus Host Range Restriction. https://jvi.asm.org/content/86/10/5857

Samji T. (2009). Influenza A: understanding the viral life cycle. The Yale journal of biology and medicine, 82(4), 153–159.

Taubenberger, J., & Morens, D. (2006, January). 1918 Influenza: The mother of all pandemics. Retrieved April 10, 2020, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3291398/

“Influenza Virus RNA Genome.” Virology Blog Header Image, 16 Dec. 2009, www.virology.ws/2009/05/01/influenza-virus-rna-genome/.