Swine Flu
(Swine Influenza A [H1N1] Virus)
Medical Author: Charles Davis, MD, PhD
Medical Editor: Melissa Conrad Stöppler, MD
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H1N1: An American in London
By Laura Lee Bloor
MedicineNet.com
Reviewed by Melissa Conrad Stöppler,
MD
 When Orange County, Calif., native Jennifer Johnson* started feeling feverish with a sore throat, headache, and body aches, one of her restaurant coworkers teased that she probably had swine flu (H1N1).
Unfortunately, the joke turned out to be real. It was a Saturday night, and 24-year-old Johnson was working as a server at a London restaurant. Her throat had been sore and scratchy all day, but she wasn't too concerned. Around 10 p.m., she felt a sudden strong fever develop in addition to some mild dizziness, loss of appetite, and painful body aches.
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What is swine flu (novel H1N1 influenza A swine flu)?
Swine flu (swine influenza) is a respiratory disease caused by viruses (influenza viruses) that infect the respiratory tract of pigs and result in nasal secretions, a barking-like cough, decreased appetite, and listless behavior. Swine flu produces most of the same symptoms in pigs as human flu produces in people. Swine flu can last about
one to two weeks in pigs that survive. Swine influenza virus was first isolated from pigs in 1930 in the U.S. and has been recognized by pork producers and veterinarians to cause infections in pigs worldwide. In a number of instances, people have developed the swine flu infection when they are closely associated with pigs (for
example, farmers, pork processors), and likewise, pig populations have occasionally been infected with the human flu infection. In most instances, the cross-species infections (swine virus to man; human flu virus to pigs) have remained in local areas and have not caused national or worldwide infections in either pigs or humans. Unfortunately, this cross-species situation with influenza viruses has had the potential to change.
Investigators think the 2009 swine flu strain, first seen in Mexico, should be termed
novel H1N1 flu since it is mainly found infecting people and exhibits two main surface antigens, H1 (hemagglutinin type 1) and N1 (neuraminidase type1). Recent investigations show the eight RNA strands from novel H1N1 flu have one strand derived from human flu strains, two from avian (bird) strains, and five from swine strains.
Why is swine flu (H1N1) now infecting humans?
Many researchers now consider that two main series of events can lead to swine flu (and also avian or bird flu) becoming a major cause for influenza illness in humans.
First, the influenza viruses (types A, B, C) are enveloped RNA viruses with a segmented genome; this means the viral RNA genetic code is not a single strand of RNA but exists as
eight different RNA segments in the influenza viruses. A human (or bird) influenza virus can infect a pig respiratory cell at the same time as a swine influenza virus; some of the replicating RNA strands from the human virus can get mistakenly enclosed inside the enveloped swine influenza virus. For example, one cell could contain
eight swine flu and eight human flu RNA segments. The total number of RNA types in one cell would be 16;
four swine and four human flu RNA segments could be incorporated into one particle, making a viable
eight RNA segmented flu virus from the 16 available segment types. Various combinations of RNA segments can result in a new subtype of virus (known as antigenic shift) that may have the ability to preferentially infect humans but still show characteristics unique to the swine influenza virus (see Figure 1). It is even possible to include RNA strands from birds, swine, and human influenza viruses into one virus if a cell becomes infected with all three types of influenza (for example,
two bird flu, three swine flu, and three human flu RNA segments to produce a viable
eight-segment new type of flu viral genome). Formation of a new viral type is considered to be antigenic shift; small changes in an individual RNA segment in flu viruses
are termed antigenic drift and result in minor changes in the virus. However, these can accumulate over time to produce enough minor changes that cumulatively change the virus' antigenic makeup over time (usually years).
Second, pigs can play a unique role as an intermediary host to new flu types because pig respiratory cells can be infected directly with bird, human, and other mammalian flu viruses. Consequently, pig respiratory cells are able to be infected with many types of flu and can function as a "mixing pot" for flu RNA segments (see Figure 1). Bird flu viruses, which usually infect the gastrointestinal cells of many bird species, are shed in bird feces. Pigs can pick these viruses up from the environment and seem to be the major way that bird flu virus RNA segments enter the mammalian flu virus population.
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Next: What are the symptoms of swine flu
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Sore Throat (Pharyngitis) »
What causes a sore throat?
A sore throat can have many causes including:
- Common viruses, and even the viruses that cause
mononucleosis (mono) and the flu, can cause a sore throat. Some viruses can also produce blisters in the mouth and throat ("aphthous stomatitis").
- Breathing through the mouth can produce throat dryness and
soreness.
- Sinus drainage (post nasal drip) may cause a sore throat.
- A sore throat can also be caused by bacteria. The two most common bacteria to cause a sore throat are Streptococcus (which causes
strep throat) and Arcanobacterium haemolyticum. Arcanobacterium causes sore throats mainly in young adults and is sometimes associated with a fine red rash.
- Sore throat appearing after treatment with antibiotics, chemotherapy, or other immune-compromising medicati...
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