Swine Flu: Questions and Answers from Harvard Medical School

By Anthony L. Komaroff, M.D.
Content provided by the Faculty of the Harvard Medical School

An epidemic of swine flu, also called H1N1 flu, that apparently developed in Mexico and the United States, now has spread to 20 countries around the world. The World Health Organization has indicated that a global pandemic is likely to develop. A pandemic is an epidemic that spreads around the whole world and is easily spread from human to human, caused by an infectious microbe (including, but not limited to, viruses) that humans have not previously been infected with. Pandemics also often cause more severe disease than epidemics, but that is not always the case. A global pandemic that causes serious illness could be bad not only for human health but also for the global economy (which definitely does not need any more bad news right now).

Q: What is "swine flu"?

A: Flu is a disease caused by the influenza virus. Humans, pigs, birds, and other animals all can be infected by influenza viruses. Typically, influenza viruses can infect only one species, so the influenza viruses of humans are different from those of pigs and birds. However, sometimes a virus can infect more than one species. For example, pigs sometimes can be infected not only with pig influenza viruses, but also with human and bird influenza viruses. Then these viruses can sidle up to one another and swap genes, creating new viruses that have a mix of genes—from human, pig, and bird viruses. That is what has happened with this new swine flu virus, which contains some genes from human, swine, and bird influenza viruses.

Sometimes this swapping of genes allows a virus that was originally able to infect only pigs or only birds to also infect humans. When that happens, we refer to the illness as "swine flu" or "bird flu." On the unusual occasion when a swine (or bird) influenza virus develops the ability to infect a human, the virus is not easily passed from human to human, and so an epidemic caused by the virus does not develop. This new swine flu virus, however, has not only developed the ability to infect humans, but also to spread from human to human. Almost surely it is transmitted by sneezing and coughing and by skin-to-skin contact (like shaking hands or kissing) with an infected person.

Q: Are swine flu or bird flu viruses dangerous?

A: When swine flu or bird flu viruses develop the ability to spread from human to human, they can be very dangerous: they can spread rapidly around the globe, and produce severe disease. In other words, they can cause a pandemic.

One reason that pandemic illness is more severe is that the virus is so new. The regular flu that comes each year is caused by a regular human influenza virus that often has similarities to the viruses that have caused the flu in years past, so most people have some degree of immunity to the latest regular human flu virus. The unusual swine flu or bird flu viruses that develop the ability for person-to-person spread are so different from regular human flu viruses that people have little or no immunity to the new virus. That is what some experts worry may be happening with the new swine flu H1N1 virus.

Q: How do I know if I've caught swine flu?

A: The initial symptoms of this flu virus are like those of the regular, annual flu viruses: fever, muscle aches, runny nose, and sore throat. Nausea, vomiting, and diarrhea may be more common with this swine flu than with the regular flu. If this epidemic hits your community and you develop flu-like symptoms, it is likely your doctor will take samples from your throat or material you cough up and send them to the state public health laboratory for testing.

Q: How do I protect myself?

A: To protect yourself from catching swine flu from others, take the same steps you would to prevent getting any cold or flu:

  • Wash your hands or use alcohol-based hand cleaners frequently.

  • When you greet people, don't shake hands or exchange kisses.

  • Avoid contact with people with flu symptoms.

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More than 200 viruses can cause the common cold. There are more than 1 billion colds in the United States each year.