Human influenza pandemics are often given nicknames like Spanish Flu or Hong Kong Flu by the general public. These nicknames usually refer to the geographical area where the virus is thought to have first appeared. Some nicknames refer to the symptoms of the disease. For example, the 1918 H1N1 flu was sometimes called "Three Day Fever."
H1N1 Influenza A is the scientific designation for the 2009 Swine Flu virus. It describes the structure of that virus.
What H1N1 Influenza A Means
All human influenza viruses belong to the Orthomyxoviridae virus family. This family includes Influenzas A, B, and C, Isavirus and Thogotovirus. Human influenza pandemics are usually caused by Influenza A.
The influenza A virus is divided into subtypes, such as H1N1. The letters H and N refer to hemagglutinin and neuraminidase. Hemagglutinin and neuraminidase are antigens, proteins that provoke an immune response in the human body.
The human body responds to antigens by producing antibodies. Antigens are categorized according to the antibodies that respond to them. There are 16 known hemagglutinin subtypes for influenza A (H1 to H16) and 9 known neuraminidase subtypes (N1 to N9). Each of these subtypes is vulnerable to a similar type of antibody.
How the Flu Virus Spreads in the Body
The human influenza virus can only reproduce inside a living host cell. Hemagglutinin and neuraminidase drive the spread of viral infection in host cells. Each viral particle is covered with hemagglutinin and neuraminidase. Hemagglutinin binds to the targeted host cell and injects the virus's genetic material into it. After the virus has reproduced inside the host cell, neuraminidase releases the offspring. The host cell then dies.
There are three hemagglutinin subtypes that are known to attack human cells: H1, H2, and H3. These three subtypes bind with cells in the human respiratory tract. Other hemagglutinin subtypes target different mammals or birds. H5, for example, attacks the digestive tracts of birds. Of the nine neuraminidase subtypes, N1 and N2 are most commonly found in humans.
New Antiviral Drugs for Influenza
The most effective anti-viral drugs currently available are called neuraminidase inhibitors. These drugs interfere with the release of viral offspring from the host cell. According to an article by Anne Moscona, M.D. published in the New England Journal of Medicine in September 2005 ("Neuraminidase Inhibitors for Influenza"), when administered within 12 hours of the onset of symptoms, neuraminidase inhibitors such as zanmivir (Relenza) and oseltamivir (Tamiflu) can shorten the duration of the illness by three or more days.
References
Protein Data Bank. (12 May 2009). "Molecule of the Month: Influenza Neuraminidase."
Protein Data Bank. (12 May 2009). "Molecule of the Month: Hemagglutinin."
Kolata, Gina. Flu: The Story of the Great Influenza Pandemic of 1918 and the Search for the Virus that Caused It. New York, U.S.: Farrar, Straus and Giroux, 1999.
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