As flu season approaches, there's been a lot of talk about bird flu. I thought I'd try to clarify some of the issues and misconceptions around this illness. I keep up with news on this and other emerging diseases in a number of ways, including Pro-MED, which is produced by the Federation of American Scientists, and the World Health Organization site. You can also read lots more at the CDC site, especially here.

Bird (avian) flu is an influenza virus type A that normally infects birds, but can also infect pigs and other animals. Wild birds, the natural hosts, normally don't get sick from this virus, but domestic animals such as chickens and turkeys can be severely affected severely. Humans, meanwhile, can be infected with influenza types A, B, and C.

Genetic changes and sharing (the closest thing viruses have to sex) can occur under certain circumstances such as in crowded conditions where poultry, pigs, and people live in close quarters. This change can allow a virus to become much more infectious to humans and more easily transmitted from person to person. And this is where a "pandemic" comes in: it's a worldwide outbreak of a new influenza A virus between humans, while epidemics tend to be seasonal, involving viruses that already exist.

For you history buffs, previous pandemics include:

1918-19: Spanish flu. Caused more than 500,000 deaths in the U.S., and 50 million worldwide.

1957-58: Asian flu. 70,000 deaths in the U.S.

1968-69. Hong Kong flu. 34,000 deaths in the U.S.

Both the 1957-58 and 1968-69 pandemics were caused by viruses containing a combination of genes from a human and an avian influenza virus. It may be reassuring to note that the number of deaths has decreased with each pandemic, possibly due to better supportive medical care.

The avian flu's jump to humans was first detected in 1997, although all the human deaths reported so far (about 60 since 2003) have been due to transmission from animals to humans. There has been more concern recently because the virus has been detected in migratory birds which can't be caught and killed - and which may carry the virus to Europe and Africa within the next two migratory seasons.

The consensus is that although it's possible an avian flu epidemic may occur, no one can predict if it will take place in weeks or years. It all depends on when that genetic shift (from birds to humans) takes place.

There has been no detection of this virus in the U.S. It is possible for travelers to be infected, but most of the cases in humans have been in those with closer contact to birds than a casual traveler has. Since the infection occurs via fecal-oral route, to reduce your risk while traveling, avoid bird markets, zoos, and areas in parks, etc. with high concentrations of bird feces.

Countries that are the most vulnerable to this flu are Indonesia, Vietnam, and Cambodia, due to their high concentration of bird markets. Other areas involved are Thailand, China (south and north), Tibet, Russia, Kazakhstan, and Mongolia. For an update on outbreaks before you travel, check the CDC info for southeast Asia and east Asia.

Symptoms of bird flu in humans have ranged from typical flu-like symptoms (fever, cough, sore throat, muscle aches) to eye infections and pneumonia. If you feel you've been exposed, there are a couple of treatment recommendations available today that you may want to discuss with your doctor. Until these are tested in a pandemic, however, their true efficacy is unknown. There are currently no vaccines available, but many companies are working on them.

Bottom line: For now, avian flu is just a "virus of interest" to medical researchers. Of course, you should always consult with your own doctor about any medical conditions or risks that concern you.