Orthomyxoviridae

Some tiny germs cause the flu.

These germs live in birds and people. They can also live in pigs and seals.

The germs have tiny spikes on their skin. These spikes help the germ stick to a person. This helps the germ get inside the body.

Flu germs can spread through the air. They move when people cough or sneeze. They can also live on surfaces for a week.

Some germs can stay cold for a long time. They can live in very cold lakes.

We can use soap to wash them away. Keeping clean helps us stay well!

Orthomyxoviridae is a large family of tiny germs. We call these germs viruses.

Many of these viruses cause the flu. They can infect birds, humans, pigs, and seals. Some even infect salmon.

These viruses have a special shape. They can be round or long like a string. On their outside, they have tiny spikes. One type of spike is called hemagglutinin. This spike helps the virus stick to a cell. It helps the virus get inside.

Another spike is called neuraminidase. This spike helps new viruses break free from a cell. This lets the virus spread to more cells.

Inside the virus are small pieces of code. We call this the genome. The genome is made of RNA. In influenza A, the genome has eight separate pieces. These pieces can mix if two different viruses meet. This mixing can make new types of flu.

Some flu outbreaks, called pandemics, come from birds. The 1918 flu was a very big pandemic. It caused many deaths around the world.

Orthomyxoviridae is a large family of tiny germs called viruses.

These viruses are very important to study because many cause the flu. They can infect many different living things. Some types infect birds, humans, pigs, and even seals. Other viruses in this family can infect salmon or mosquitoes.

Because they affect so many animals, scientists watch them closely.

These viruses work in a very specific way to spread. First, a spike on the virus called hemagglutinin sticks to a cell.

The cell then pulls the virus inside itself. Once inside, the virus releases its genetic code into the cell's nucleus. The cell is then forced to make new viral parts. These parts gather at the cell's edge to form new viruses. Finally, a spike called neuraminidase helps the new viruses break free.

This allows the infection to spread to more cells.

Scientists have learned a lot about these viruses over time. They use special names to keep track of different types. For example, influenza A viruses are named using their H and N proteins. These proteins are the spikes on the outside of the virus.

There are 18 different H subtypes and 11 different N subtypes known. Knowing these names helps doctors understand which flu is spreading. This helps them prepare for new outbreaks.

History shows us how powerful these viruses can be. Some outbreaks, called pandemics, affect the whole world.

The Spanish flu happened from 1918 to 1920. It was caused by the H1N1 subtype and caused many deaths. Another big one was the Asian Flu in 1957. This was caused by the H2N2 subtype. More recently, the 2009 swine flu pandemic was also caused by H1N1. These numbers show how much these viruses can change.

Understanding these viruses helps us stay healthy in our daily lives. We know that flu viruses can live on surfaces for about one week.

They can also live for a long time in very cold places. This is why washing hands with soap is so helpful. Detergents and disinfectants can easily stop these viruses from working. By learning how they move, we can better protect ourselves and our pets.

Orthomyxoviridae is a large family of negative-sense RNA viruses.

These viruses are significant because they include several genera that cause influenza in humans and animals. The family is divided into nine distinct genera. These include Alphainfluenzavirus, Betainfluenzavirus, Gammainfluenzavirus, and Deltainfluenzavirus. Other genera like Isavirus infect salmon. Some, called arboviruses, infect both vertebrates and invertebrates, such as mosquitoes or ticks. This diversity makes the family a major focus for biological study.

The structure of an influenzavirus virion is pleomorphic, meaning it can take different shapes.

It can appear as a sphere or as a long filament. Most particles are ellipsoidal and measure between 100 and 120 nm in diameter. Filamentous forms can be up to 20 μm long. The surface is covered in about 500 spike-like projections. The most important spikes are glycoproteins called hemagglutinin (HA) and neuraminidase (NA). The ratio of HA to NA is approximately 10 to 1. These spikes are anchored in a lipid bilayer membrane.

The virus operates through a complex replication cycle.

First, the hemagglutinin protein binds to sialic acid sugars on a host cell. This occurs on epithelial cells in the throat or lungs. The cell then brings the virus inside through endocytosis. Inside an acidic environment called an endosome, the viral envelope fuses with the cell membrane. This releases the viral RNA (vRNA) and polymerase proteins into the cytoplasm. These components then travel into the host cell nucleus to begin replication.

Because these viruses cannot make their own messenger RNA (mRNA), they must use a process called cap snatching.

The viral protein PB2 binds to the 5' capped end of a cellular pre-mRNA. Then, the protein PA cleaves this cellular fragment to use as a primer. This allows the virus to create mRNA that the cell's ribosomes will recognize. The virus also uses its RNA-dependent RNA transcriptase to copy its genome. However, this enzyme lacks proofreading abilities. It makes an error roughly every 10,000 nucleotides, meaning almost every new virus contains mutations.

Influenza A viruses are categorized by their specific H and N subtypes.

Scientists have identified 18 HA subtypes and 11 NA subtypes in nature. These proteins are the primary targets for antibodies and antiviral drugs. The genome is also divided into six to eight segments of linear RNA. If two different influenza viruses infect the same cell, these segments can mix. This process is called reassortment. Reassortment can lead to an antigenic shift, which creates viruses with new behaviors or the ability to infect new species.

History shows the impact of these viruses through global pandemics.

The 1918 Spanish flu pandemic was caused by the H1N1 subtype and killed between 20 and 100 million people. The 1957 Asian Flu, caused by H2N2, resulted in 1 to 1.5 million deaths. The 1968 Hong Kong Flu, caused by H3N2, killed between 0.75 and 1 million people. More recently, the 2009 swine flu pandemic was caused by H1N1 and resulted in up to 395,600 deaths. These events highlight how rapidly the virus can change and spread.

Understanding the movement and survival of these viruses is essential for public health.

Influenza viruses can stay infectious on surfaces for about one week at human body temperature. They can survive for over 30 days in cold environments. In very low temperatures, like Siberian lakes, they can remain infectious indefinitely. However, they are easily destroyed by detergents and disinfectants. By studying how these viruses interact with hosts and environments, researchers work to develop better protections and treatments.