Influenza A virus

A tiny germ causes the flu.

This germ lives in many animals. It lives in birds and pigs. It can also live in dogs.

The germ can make people sick. You might have a cough. You might have a fever too. Some people feel very bad. It can make it hard to breathe.

We can use shots to stay well. Doctors also use medicine to help. We can learn more about these germs.

Influenza A is a tiny germ that causes the flu.

It lives in many animals. It stays in birds, pigs, horses, and dogs. It can also make people sick.

Scientists name the virus using special codes. They look at two proteins on its surface. We call these proteins hemagglutinin and neuraminidase.

We use the letters H and N for them. For example, H1N1 means it has one type of H and one type of N. The virus changes its shape often. This is called mutation. These changes help the virus hide from our bodies.

Sometimes, the virus causes a pandemic. A pandemic is when a new flu spreads across the whole world. The Spanish Flu happened from 1918 to 1920. It caused many deaths.

When people get the flu, they may have a fever or a cough. They might feel muscle aches. Some people get very sick and have trouble breathing. We can use vaccines to help stay safe. Doctors also use special medicines to treat it.

A global group of labs watches the virus every year. They test millions of samples to keep us safe.

Influenza A virus, or IAV, is a tiny germ that makes people and animals sick.

It is a pathogen, which is a word for something that causes disease. This virus lives in many different living things. It is always moving through birds, pigs, horses, and dogs. Sometimes, it can even jump from animals to humans. When it spreads to many people all over the world, it is called a pandemic. One famous example was the Spanish Flu from 1918 to 1920. That event caused between 20 and 50 million deaths worldwide.

To understand how the virus works, we have to look at its tiny body. The virus is shaped like a small oval or a long string. It is very small, measuring only 80 to 120 nanometers across.

Inside the virus, there are eight separate pieces of genetic material called RNA. These pieces act like a tiny instruction manual for the virus. The virus has a protective outer layer called an envelope. On this envelope, there are two special spikes called proteins. One protein is hemagglutinin, which helps the virus grab onto a host cell. The other is neuraminidase, which helps new viruses escape the cell to spread.

Scientists use a special naming system to keep track of these different viruses. They look at the two proteins on the surface to name a subtype. We use the letter H for hemagglutinin and N for neuraminidase. For example, the name H5N1 means it has type-5 H and type-1 N.

There are 18 known types of H and 11 types of N. Most of these combinations can be found in wild birds. The virus also changes through a process called mutation. This means the virus makes small mistakes when it copies itself. These changes help the virus hide from our bodies' defenses.

We can learn a lot about the history of this virus by looking at the past. Scientists think these viruses might have started in water a very long time ago. Some studies suggest they may have even come from tiny creatures like crustaceans 600 million years ago. The Influenza A virus and Influenza B virus split from a single ancestor about 4,000 years ago.

We have records of flu-like sickness going back to ancient times. A man named Hippocrates wrote about it in 412 BCE. In Japan, a historian named Fujikawa recorded 46 outbreaks between the years 862 and 1868.

Even though the flu can be serious, there are many ways to stay safe.

Most people with the seasonal flu feel a fever, a cough, or sore throats. Some people might even have trouble breathing. To help, doctors use vaccines to teach our bodies how to fight the virus. They can also use antiviral medicines if someone gets sick early. A huge global network called the GISRS watches the virus every year. This network has laboratories in 127 different countries. They test millions of samples to help make new vaccines. This helps us stay one step ahead of the changing virus.

Influenza A virus, or IAV, is a significant pathogen that causes seasonal flu in humans. It is the only species within the genus Alphainfluenzavirus. This virus is highly versatile because it infects many different hosts. While it causes seasonal illness in humans, it also circulates constantly in bats, pigs, horses, and dogs. Some mammals may also be infected occasionally. IAV is a major concern for global health because it can cause pandemics. A pandemic is when a virus spreads to many people across the world. One of the most notable examples was the Spanish Flu pandemic from 1918 to 1920.

To understand how IAV functions, we must look at its complex structure. The virus particle, known as a virion, is 80 to 120 nanometers in diameter. Some smaller virions are elliptical, while larger ones are filamentous. The virus has a negative-sense, single-stranded, segmented RNA genome. This genome is enclosed in a lipid envelope derived from the host cell. Inside the core, the viral RNA is made of eight separate segments. A protein called nucleoprotein (NP) coats this RNA to form a ribonucleoprotein (RNP). This RNP has a helical or spiral configuration. Three large proteins, PB1, PB2, and PA, bind to each segment to assist with replication.

The mechanism of infection involves specific proteins on the viral envelope. Two primary antigenic proteins, hemagglutinin (HA) and neuraminidase (NA), act as spikes on the surface. Hemagglutinin allows the virus to bind to host cells, which enables the RNA to invade. Once bound, the M2 protein forms an ion channel in the envelope. This channel helps the virus uncoat, exposing its contents to the host cell's cytoplasm. Inside the host cell nucleus, the virus performs transcription and replication. The viral RNA polymerase complex uses a process called cap-snatching to hijack host cell mRNA. This allows the virus to manufacture its own viral proteins using the host's ribosomes.

Scientists classify IAV subtypes using the combination of these surface proteins. There are 18 known types of hemagglutinin and 11 types of neuraminidase. A subtype name like H5N1 describes a virus with type-5 HA and type-1 NA. Almost all possible combinations of H and N proteins have been found in wild birds. However, H17 and H18 have only been discovered in bats. The virus changes through mutation and genetic reassortment. Mutation involves small errors during copying, while reassortment can happen when different strains mix. These changes allow the virus to evade the immune system and jump between different species.

The history of influenza is incredibly long and spans many millennia. Recent studies suggest that influenza viruses may have an aquatic origin. Some evidence indicates that viruses in the Articulavirales order may have evolved from crustaceans over 600 million years ago. The subtypes of IAV are estimated to have diverged about 2,000 years ago. Influenza A and B diverged from a single ancestor roughly 4,000 years ago. Records of flu-like diseases go back to 412 BCE with Hippocrates. In Japan, the historian Fujikawa documented 46 epidemics between 862 and 1868.

Major pandemics have shaped human history through the spread of IAV. The 1918 Spanish Flu was caused by an H1N1 subtype and killed an estimated 20 to 50 million people. In 1957, the "Asian flu" pandemic was caused by an H2N2 subtype. This virus resulted from reassortment between avian strains and the 1918 virus. The 1968 "Hong Kong flu" pandemic involved an H3N2 subtype. In 2009, a new H1N1 strain emerged, which was often called "swine flu" due to its resemblance to pig viruses. These historical events show how quickly the virus can change its impact on the global population.

Managing influenza requires constant global cooperation and scientific monitoring. The Global Influenza Surveillance and Response System (GISRS) tracks the spread of the virus worldwide. This network includes laboratories in 127 countries that test several million specimens every year. GISRS monitors human viruses as well as avian and swine strains that could infect people. This data helps scientists develop both seasonal and pandemic vaccines. Because the virus changes so often, vaccines must be reformulated regularly. In humans, seasonal flu can be managed with vaccines or antiviral medicines. In poultry, biosecurity measures like quarantine and hygiene are used to prevent outbreaks.