Influenza, commonly known as "the flu", is an infectious disease caused by an influenza virus. There are four types of influenza virus, types #influenza_A and B (seasonal), C which is less frequent causing mild infections and not a public health threat, and D which primarily infects cattle and is not known to infect or cause illness in people.
Seasonal influenza is characterized by a sudden onset fever or feeling feverish/chills, a cough (usually dry), headache, muscle pain and joint pain, severe malaise (feeling unwell), fatigue, sore throat and runny or stuffy nose. Vomiting and diarrhea is more common in children than adults.
Influenza A[edit | edit source]
Influenza A is a major subtype of flu viruses, there are 18 known HA and 11 NA subtypes of influenza A, although of those that can infect humans only H1N1 and H3N2 are currently in wide circulation.
Avian flu[edit | edit source]
Avian influenza viruses are influenza A viruses, and infect birds including chickens, ducks and wild birds but rarely infect people. Influenza A virus subtypes H5, H7 and H9 are the most likely to infect humans, particularly H5N1 and H7N9. H5N1 has infected people in 16 different countries, and kills around 50% of people it infects.
Swine flu[edit | edit source]
Swibe flu is the subtype of influenza A known as H1N1.
Influenza B[edit | edit source]
The other main type of flu is influenza B.
Influenza C[edit | edit source]
Influenza C is less common than influenza A and B.
Influenza D[edit | edit source]
Influenza D is less common than influenza A or influenza B.
Epidemiology[edit | edit source]
All age groups can be infected with flu but there are groups that are at more risk than others.
- children under 59 months
- health care workers
- pregnant women
- individuals with chronic medical conditions
- individuals with immunosuppressive conditions
Influenza spreads easily with rapid transmission in crowded areas such as schools and nursing homes. Sneezing and coughing spreads droplets containing viruses which can spread over three feet. Persons within range can become infected by breathing in these droplets. The virus also spreads by hands contaminated with influenza. From time of infection to illness is about 2 days but can be one to four days.
See also[edit | edit source]
Learn more[edit | edit source]
- Flu Symptoms - What are the emergency warning signs of flu sickness? (Adults, children, and infants.)
- Influenza Video short
- Influenza (Seasonal) Fact Sheet - World Health Organization
- Influenza A subtypes - CDC
- H5N1 - CDC
References[edit | edit source]
- "Influenza (Seasonal)". World Health Organization. Retrieved August 25, 2018.
- "Flu Symptoms & Complications | Seasonal Influenza (Flu)". Centers for Disease Control. June 5, 2018. Retrieved August 25, 2018.
- "Influenza Type A Viruses | Avian Influenza (Flu)". Centers for Disease Control. February 10, 2020. Retrieved March 22, 2021.
- "Influenza". Blausen Medical. November 19, 2015. Retrieved August 25, 2018.
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Centers for Disease Control and Prevention (CDC) - The Centers for Disease Control and Prevention is a U.S. government agency dedicated to epidemiology and public health. It operates under the auspices of the Department of Health and Human Services.