There are many types of influenza, but the strain that currently has health officials worried is H5N1. At the moment, the disease mostly affects birds. An estimated 150 million birds have either died of the disease -- or been killed in an attempt to stop its spread.
The first human case of H5N1 occurred in Hong Kong in 1997; 18 people were infected and six died. Since then, infections have been confirmed in more than 100 people, with 60 fatalities.
So far, no human infections have been reported outside of Asia, but in recent weeks avian influenza has reached Europe.
In a two-part report, NPR asked health experts to answer listeners' questions about bird flu. First, Dr. Hon Ip, director of the United States Geological Survey's Diagnostic Virology Laboratory at the National Wildlife Health Center in Madison, Wis., answers questions about the virus and how it spreads. In part two, Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, answers questions about the government's preparations for a potential outbreak, and what individuals could do to stay safe.
Part One: Q & A with USGS Virologist Dr. Hon Ip
Q: Can any migrating bird carry the flu virus or are there only certain types of birds that will spread the flu? -- Laura Burrone, New Haven, Connecticut
A: Not every species of birds is equally susceptible to the flu virus, and not just migratory birds are susceptible. Avian influenza viruses are found more commonly in water birds (ducks and geese), shorebirds and gulls. Birds such as sparrows and pigeons tend not to be as readily infected. It is not clear why shorebirds are more susceptible to avian influenza infections and simple access to water is not the answer, as even when birds are exposed directly to the virus, species such as pigeons are more resistant.
Q: Has it been determined how long the virus survives on feathers and down? Does the infectious agent die off in a certain number of hours or does it have to be killed off via heat, etc.? -- Valerie Doyle, Acton, Maine
A: Unfortunately, there is not a simple answer. Influenza viruses are fairly environmentally resistant, which means they can survive for long periods of time in the wild. The virus on feathers and down is usually from fecal contamination and we know that the virus remains infectious in contaminated feces for almost a week at room temperature and up to three weeks in the cold.
There are a number of ways to kill the virus -- heat is a good way. But just simple soap and water are excellent. Also many disinfectants and commercial cleaners will work. The USDA Web site has a number of examples of what can be used. (Adobe Acrobat required.)
Q: Can mosquitoes be a vector for the spread of avian flu virus? -- Carol Taylor, Lovington, New Mexico
A: Influenza is not normally a disease that is transmitted by a vector such as a mosquito. But because the virus is relatively environmentally stable, mechanical transmission by insects, such as flies, is a possibility. Since the virus can survive for long periods in the wild, flies might pick it up when they land on feces or infected birds, and then carry it to other animals. Mosquitoes typically transmit diseases, such as West Nile Virus, by ingesting blood from infected animals, then transmitting it to the next animal they feed on.
Q: What early symptoms of bird flu should someone look for? -- Anne Brodie, Aurora, New York
A: The true highly pathogenic avian influenza H5N1 can cause very rapid death in susceptible birds. Sometimes the first sign is that birds have died without obvious clinical symptoms.
When signs of infection are present, the birds may have respiratory symptoms such as sneezing and coughing, swelling of the eyes and combs and wattle, their feathers are ruffled, they stop laying eggs, and they may have diarrhea.
Q: What makes this strain of bird flu so virulent (and does this mean it spreads more easily or makes people sicker, or both?) -- Candy McLaughlin, Lexington, Massachusetts
A: That is a great question and not only is the answer complicated, we don't have all the answers.
There are a number of genetic differences in the H5N1 virus that, for example, allow the virus to grow in cells throughout the body of a bird. Other avian influenza strains can only grow in the respiratory and intestinal tracts. This allows the H5N1 virus to cause more damage to more organ systems.
Other genetic changes allow the H5N1 virus to bind to surface molecules on human cells, something that other avian influenza viruses cannot do. Since binding is a necessary first step of getting into the cell for the virus to replicate, these kinds of changes (which are in the hemagglutinin protein) allow the H5N1 avian virus to infect people.
Q: Is the media exaggerating the potential danger of bird flu? -- Joyce Kuzmin, Boston, Massachusetts
A: There is a lot of coverage in the media, and it's hard to keep up with what everyone is saying, but I think the issue is important. Highly pathogenic, H5N1 is a clear danger to poultry and its threat to wild birds is real. Although the number of human cases has been small so far, the potential for the virus to change into a more serious threat to humans is also real. So some level of public awareness, including media coverage is appropriate.
Q: What's the probability of an individual U.S. resident contracting avian flu at this point compared to other events, such as being struck by lightning? -- Len Anderson, Sylvania, Ohio
A: As of right now, there is no evidence of bird flu being in North America. Not in people, not in poultry, not in wildlife. In the United States, on average, something like 82 people die per year from lightning, so since bird flu is not yet in this country, I would say that the possibility of a U.S. citizen dying from lightning is much higher than dying from H5N1 -- at the moment.
Q: I'm wondering what is the vector of transmission from bird to human? Do you have to be in contact with bird feces? Do you have to be in contact with bird blood products? How is it transmitted from the bird to the human being? -- Chris (Last Name Not Provided), Brewster, New York
A: Almost all human cases have been traced to close contact with infected poultry. We think the process of raising chickens and preparing chickens in Asia -- the home slaughter, plucking feathers, preparing it for the table -- introduces a number of ways in which a person can become infected. There have been very limited examples of human to human transmission. I think that it's really extended, prolonged contact with poultry -- as they are struggling, flapping their feathers, releasing dander and other material -- that is probably the route of infection.
Contact with bird feces, yes, that is definitely a way people could become infected. Eating raw, contaminated (poultry) blood has been suggested as one of the ways people have become infected in Vietnam.
Q: Is it possible for migrating birds to carry the virus to North America, or is exposure here more likely from people returning to North America from other parts of the world that had the virus? With the new strain of bird flu reaching places like Romania and Turkey, should I reconsider my plans to travel there next year? -- Bob Spaziano, Raleigh, North Carolina
A: Both are possible. It's definitely possible for migratory birds to carry H5N1 to North America. We at the Department of Interior and our sister agencies are trying to figure out how likely that is. We think that international travel was a major way that the SARS virus, which also originated in Asia, spread rapidly around the world, so I would say that both migratory birds and international traffic are ways that the virus could come to this country.
You should check with the CDC and follow their latest guidelines for travel to that region of the world.
Q: Can humans get bird flu by eating the meat of infected birds? -- Claudia Sandberg Larsen, Sacramento, California
A: Not if they thoroughly cook it first. The flu virus is readily killed by temperatures reached in meat when the meat is completely cooked, and that is about 160, 170 degrees Fahrenheit.
Q: Does owning a caged pet bird increase the possibility of passing or catching the avian flu virus? -- Lisa Branson, Torrance, California
A: Having a pet bird that's inside all the time, I don't think that's a risk. Let me point out that it's illegal in the U.S. to import pet birds from regions that are infected with bird flu. So the likelihood of getting a pet bird that's already infected with bird flu is relatively low.
Q: Let's say my dogs pick up a dead bird, a bird that died from avian flu. Are my dogs at risk? -- Phil Travers, San Antonio, Texas
A: What we know today is that there is no reputable report of H5N1 being in any dogs around the world. The virus has surprised us at every turn, and so I wouldn't say that it's impossible, but at the moment, I don't think if a dog picked up a bird infected with bird flu, that the dog would be likely to come down with bird flu.
Q: What "mutation" of the virus would have to happen for it to change to person-to-person, and what factors would cause that mutation? -- Sarah (Last name not provided), Denver, Colorado
A: That's a question that a lot of virologists are trying to answer. And what we're trying to do is compare the genetic sequences of H5N1 with other known human pathogenic viruses. What we know, for example, is that mutations on the hemagglutinin gene -- that's the "H" in the H5N1 -- can allow the virus to bind better to cells in the human respiratory tract. There are also mutations in a gene called PB2 that seems to be important for infections into humans.
How quickly can it mutate? That's a very difficult question to answer. There are a number of ways in which the virus can mutate. It can mutate gradually over time, or it can recombine in a co-infection in a person or in an animal, and when recombination happens, that can introduce a lot of mutations very rapidly.
Q: Wouldn't we assume that this virus would be potentially mutating in infinitely different ways in different instances? -- NPR's Robert Siegel
A: That is quite correct, the virus is mutating randomly and it's only when a particular mutation is advantageous for it to infect a particular new host that the mutation becomes selected and takes over.
Q: How big a threat is this to healthy adults? -- Audra Bassett, Robbinsville, North Carolina
A: In a general flu epidemic or pandemic, the sick and the elderly are a target and vulnerable population, because they are less able to fight off an infection. According to the World Health Organization data, what we know about the situation in Asia is that healthy adults are being infected (by H5N1). In fact, the average age of those infected in Vietnam seems to be between the ages of 17 and 31. This could be due to occupational exposure, or it could be from a particular predilection of the virus, and I don't think there are enough cases for us to know that at the moment.
Q: Based on what we know about the migration paths of birds, does that lead you in any particular direction of where this virus might spread? -- NPR's Melissa Block
A: We had initially anticipated that the virus would spread from Southeast Asia up along the Asian continent over toward Siberia, and possibly contact migratory birds in North America over in the region of Russian Siberia and Alaska. But since this summer it looks like the virus has really spread toward Central Asia and now into Romania and Turkey. What this indicates to us is that the virus is spreading along a different route -- spreading toward the Black Sea and the Mediterranean fly way.
Now, at the moment, if the virus really is being spread by migratory birds -- and there's only circumstantial evidence for that -- it will spread potentially toward the countries around the Mediterranean basin and possibly toward regions of Africa.
There are a handful of species that migrate from North America to Europe. Where (the virus) now is, we do not think those (North American) birds are going to be in contact with the current migratory birds that are in the Black Sea.
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