Alphainfluenzavirus

Influenza A virus

History

1918-1919: Spanish Flu (H1N1)

The most deadly influenza pandemic, known as the Spanish Flu, sweeps across the world. An estimated 50 million people die, with one-third of the world's population infected.

1957-1958: Asian Flu (H2N2)

Emergence of a new Influenza A virus subtype H2N2 leads to the Asian Flu pandemic. It causes approximately 1-2 million deaths worldwide.

1968-1969: Hong Kong Flu (H3N2)

A new Influenza A virus subtype H3N2 causes the Hong Kong Flu pandemic, resulting in around 1 million deaths globally.

1977: Russian Flu (H1N1)

H1N1 resurfaces after a 20-year absence in an event known as the Russian Flu. It primarily affects younger people, who had no prior immunity.

1997: Avian Flu (H5N1)

The first known transmission of H5N1 from birds to humans occurs in Hong Kong, leading to six deaths. This strain is particularly lethal but not easily transmissible between humans.

2009: Swine Flu Pandemic (H1N1pdm09)

A novel Influenza A H1N1 virus, which originated from pigs, emerges and spreads globally as a pandemic. It is less lethal than initially feared, and vaccines are rapidly developed.

2013: H7N9

Cases of human infection with a new avian influenza A (H7N9) are reported in China. This virus causes severe respiratory illness, but does not spread easily between people.

Genomic Structure

Influenza A virus is an RNA virus that contains a segmented negative-strand RNA genome, typically comprising eight single-stranded RNA segments, each encoding one or more viral proteins.

CDS	Function
Polymerase Basic Protein 2 (PB2)	It is part of the influenza virus RNA polymerase complex responsible for viral RNA replication and transcription.
Polymerase Basic Protein 1 (PB1)	It's a crucial component of the viral RNA polymerase complex essential for the synthesis of viral nucleic acids.PB1-F2 is a protein associated with the virulence of the virus and may be involved in modulating the host immune response.
Polymerase Acidic Protein (PA)	It's the third component of the influenza RNA polymerase complex, assisting in viral RNA synthesis alongside PB1 and PB2. PA-X is a regulatory protein that may play a role in controlling host cell protein synthesis and viral pathogenicity.
Hemagglutinin (HA)	It is a glycoprotein on the surface of the virus enabling the recognition and attachment to host cell receptors, key for virus entry into host cells.
Nucleoprotein (NP)	It binds to the virus's RNA, forming ribonucleoprotein complexes that support the activity of the RNA polymerase complex.
Neuraminidase (NA)	It's another glycoprotein on the surface of the virus that facilitates the release of virus particles, helping newly synthesized virus particles detach from the host cell surface.
Matrix Protein 1 (M1) and Ion Channel Protein (M2)	M1 is the primary structural protein of the virus particle, providing structural support. M2 stands for Ion Channel Protein. It participates in the acidification process of virus particles, aiding in the release of the virus from endosomes into the host cytoplasm.
Nonstructural Protein 1 (NS1) and a small ribonucleoprotein derivative NEP (NS2)	NS1 is involved in suppressing the host's immune response, helping the virus evade host immune surveillance. NEP (Nuclear Export Protein), also known as NS2 (Nonstructural Protein 2), is involved in several steps of virus replication, including transport and packaging of viral nucleic acids.

Epidemiological Study

1、Global Epidemics and Seasonal Outbreaks

Annually, the Influenza A virus causes multiple outbreaks of varying intensity and scope around the world. Seasonal influenza typically occurs during the winter months, whereas pandemics can occur at any time and are not seasonally bound.

2、Host Diversity and Viral Variation

The Influenza A virus is capable of infecting a wide range of hosts, which increases its genetic diversity due to the reassortment of gene segments between different species. There is a risk of pandemics when flu viruses are transmitted from animals (such as birds or swine) to humans, especially when there is no pre-existing immunity to the newly emerged viral strain in the human population.

3、Antigenic Drift and Shift

The Influenza A virus often undergoes minor genetic mutations (antigenic drift), which can lead to decreased vaccine effectiveness. More extensive genetic changes (antigenic shift) can result in the emergence of new subtypes, increasing the possibility of flu pandemics.

4、Influenza Pandemics

Historically, the 1918 Spanish Flu, the 1957 Asian Flu, the 1968 Hong Kong Flu, and the 2009 A(H1N1)pdm09 influenza were all caused by Influenza A viruses with new combinations of HA and NA subtypes. These viruses often spread rapidly due to a lack of pre-existing immunity in humans.

5、Surveillance and Control Measures

To reduce the impact of the Influenza A virus, the World Health Organization (WHO) and national health agencies have implemented a range of surveillance measures. This includes the Global Influenza Surveillance and Response System (GISRS), periodic updates of the influenza vaccine composition to match circulating viral strains, and advocating for intensified personal and public health measures during flu season.

Preventive Tips

Get Vaccinated

The flu vaccine is the best way to prevent influenza. Getting vaccinated annually can offer immunity against the prevalent strains of the virus.

Wash Hands Frequently

Practice good hand hygiene by washing with soap and water, especially after touching public surfaces, and before eating.

Avoid Touching Your Face

Avoid touching your eyes, nose, and mouth with unwashed hands.

Social Distancing

Stay away from sick people and reduce gathering in large numbers during the flu season.

Healthy Habits

Maintain good lifestyle habits, such as getting enough sleep, eating a balanced diet, exercising regularly, and staying hydrated.

Clean Surfaces

Regularly clean and disinfect surfaces and objects that may be contaminated with viruses.

Respiratory Hygiene

Cover your mouth and nose with a tissue when you cough or sneeze, or use your elbow if a tissue isn't available, then wash your hands immediately.

Symptom Relief

Rest

Ensure you get plenty of rest to help your body recover.

Stay Hydrated

Drink plenty of fluids like water, soup, or other beverages to prevent dehydration.

Medication

Use fever reducers and pain relievers such as ibuprofen or acetaminophen to alleviate fever and aches, but always follow medical advice.

Moisturize the Air

Using a humidifier or inhaling steam can help relieve cough and sore throat.

Nutritional Support

Maintain a nutritious diet to help support the immune system.

Introduction