H1N1 Virus Structure and Virus

Instructor: Erin Noble

Erin has a Ph.D. in Microbiology and Immunology.

The H1N1 virus can cause quite serious illness, and even death. This lesson will describe H1N1's viral proteins and how they to work together in an infected cell to replicate and produce more viruses.

Influenza Viruses

The H1N1 virus is a strain of influenza that caused a worldwide pandemic outbreak in 2009. Like other influenza viruses, it causes a respiratory infection that spreads from person to person by coughing and sneezing.

Influenza viruses are categorized into three groups: influenza A, influenza B, and influenza C. The most common cause of disease in humans is from influenza A viruses, which are further classified into strains based on their surface proteins: HA and NA. The different types of HA and NA proteins are numbered so strains of influenza are named things like H3N2 or H1N1. These strains shift and evolve over time, which is why you have to get an influenza vaccine every year. Slight changes in the strain lead to smaller seasonal outbreaks, whereas a big change in the virus can lead to huge worldwide outbreaks known as pandemics.

The H1N1 Strain

The H1N1 strain is thought to have originated in pigs, hence the common name 'swine flu', but spread very efficiently in people. In 2009, this strain caused a worldwide pandemic and is estimated to have caused over a quarter of a million deaths worldwide. The virus infects cells in the lining of the human respiratory tract and lungs, causing symptoms like coughing, sore throat, and fever. When an infected person coughs or sneezes, they spread the virus into the air and onto surfaces. This makes it easy for the virus to spread to other people.

Viral Structure

Influenza viruses are typically round but can also be amorphous or even form long, string-like filaments. Each virus has a membrane taken from the infected cell that produced it. There are several important viral proteins on this outer layer giving the virus a studded appearance.

Electron Micrograph Showing Influenza Viruses
Electron Micrograph of Influenza Viruses

HA (hemagglutinin) allows the virus to bind to cells in the respiratory tract by binding to sialic acid on the cell surface. NA (neuraminidase) helps newly made viruses release from infected cells by cutting up sialic acids so they fall off the cell. M2 (matrix protein 2) is the other protein found in the viral membrane. It is an ion channel, which means it lets the pH inside the virus change as the pH outside the virus is changed. The inside of the viral membrane is coated with M1 (matrix protein 1).

Influenza viruses have a single-stranded RNA genome that encodes all the viral proteins. This genome is divided into eight segments. Each segment is coated with NP (nucleoprotein) to protect the fragile RNA. The RNA is replicated by a polymerase composed of three different proteins: PB1, PB2, PA. Together, the RNA, NP, and polymerase are called an RNP (ribonucleoprotein particle). Two other viral proteins, NS1 (non-structural protein 1) and NS2 (non-structural protein 2), are also present within the virus in small amounts. NS1 helps to prevent the cell from detecting the virus and shutting down important cellular pathways. NS2 plays a role in assembly of new viruses.

Structure of Influenza Virus
Influenza Virus Structure

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