Influenza, commonly referred to as the flu, is an
infectious disease caused by
RNA viruses of the
family Orthomyxoviridae (the influenza viruses), that affects
birds and
mammals. The name influenza comes from the
Italian influenza, meaning "influence" (
Latin: influentia). The most common symptoms of the disease are
chills,
fever,
sore throat,
muscle pains, severe
headache,
coughing,
weakness and
general discomfort.
[1] Fever and coughs are the most frequent symptoms. In more serious cases, influenza
causes pneumonia, which can be fatal, particularly for the young and the elderly. Although it is often confused with the
common cold, influenza is a much more severe disease and is caused by a different type of virus.
[2] Influenza may produce
nausea and
vomiting, particularly in children,
[1] but these symptoms are more common in the unrelated disease
gastroenteritis, which is sometimes called "stomach flu" or "24-hour flu".
[3]Typically, influenza is transmitted from infected mammals through the air by coughs or sneezes, creating
aerosols containing the virus, and from infected birds through their
droppings. Influenza can also be transmitted by
saliva,
nasal secretions,
feces and
blood. Infections also occur through contact with these
body fluids or with contaminated surfaces. Flu viruses can remain infectious for about one week at
human body temperature, over 30 days at 0
°C (32
°F), and for much longer periods at very low temperatures.
[4][5] Influenza viruses can be inactivated by
disinfectants and
detergents.
[6][7][8] As the virus can be inactivated by soap, frequent hand washing reduces the risk of infection.
Flu spreads around the world in
seasonal epidemics, resulting in the deaths of hundreds of thousands annually — millions in
pandemic years. Three influenza pandemics occurred in the 20th century and killed tens of millions of people, with each of these pandemics being caused by the appearance of a new
strain of the virus in humans. Often, these new strains result from the spread of an existing flu virus to humans from other animal
species. An avian strain named
H5N1 raised the concern of a new
influenza pandemic, after it emerged in Asia in the 1990s, but it has not
mutated to a form that spreads easily between people.
[9] In April 2009 a novel H1N1 flu strain that combined genes from human, pig, and bird flu, initially dubbed the "
swine flu", emerged in Mexico, the United States, and several other nations. By late April, the H1N1 swine flu was suspected of having killed over 150 in Mexico,
[10] and prompted concern that a new pandemic is imminent. However, confirmed cases were lower, with only 10 deaths by the end of April, 9 in Mexico and only 1 in the US.
[11]Vaccinations against influenza are usually given to people in
developed countries [12] and to farmed poultry.
[13] The most common human vaccine is the trivalent
influenza vaccine (TIV) that contains purified and inactivated material from three viral strains. Typically, this vaccine includes material from two
influenza A virus subtypes and one
influenza B virus strain.
[14] The TIV carries no risk of transmitting the disease, and it has very low reactivity. A vaccine formulated for one year may be ineffective in the following year, since the influenza virus evolves rapidly, and different strains become dominant.
Antiviral drugs can be used to treat influenza, with
neuraminidase inhibitors being particularly effective.
