Q&A: A Swine Flu Crisis?

An epidemic of swine flu has recently developed in Mexico and the United States, says the CDC. Swine flu has killed many people, and the outbreak has features that suggest it could become a global pandemic. A pandemic is an epidemic that spreads around the whole world. Pandemics also often cause more severe disease than epidemics.

As of Sunday, April 27, the United States has declared a public health emergency, and suspect or confirmed cases are being reported from many parts of the world. If a pandemic happens, it could be very serious for human health and the global economy (which definitely does not need any more bad news right now).

What are "swine flu" and "bird flu"?
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.

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." This current virus could actually be called "swine/bird flu," since it has some genes from pig flu viruses and other genes from bird flu viruses. However, for simplicity sake, it is just being referred to as "swine flu."

Are swine flu or bird flu viruses dangerous?
Most viruses that cause swine flu or bird flu are very hard to pass from one human to another: they don't cause epidemics. Sometimes, however, further changes in genes create a virus that can spread rapidly among humans, and can produce a more severe illness. One reason this 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 people have some degree of immunity to the latest virus. The unusual swine flu or bird flu viruses that develop the ability for person-to-person spread are so different that people have little or no immunity to them. That is what some experts worry may be happening with swine flu.

How bad can a global pandemic be?
The worst global pandemic in modern times was the influenza pandemic of 1918 to 1919. It affected about a third of the human race, and killed at least 40 million people in less than a year—more than have been killed by AIDS in three decades. The world economy went into a deep recession. The average length of life dropped for 10 years. In other words, global pandemics can be a really big deal. On the other hand, other pandemics have been considerably less serious than the 1918 to1919 influenza pandemic.

Can this new swine flu virus be easily transmitted from person to person?
Unfortunately, the new swine flu virus can be transmitted between humans. It is not clear yet how easily it is transmitted, nor how it is transmitted. Almost surely it is transmitted by sneezing and coughing, and by skin-to-skin contact (like shaking hands or kissing) with an infected person.