Bird flu: the facts you need to know.

In 1997, bird flu--an illness that normally spreads from bird to bird--jumped the species barrier. It began spreading from birds to humans. Since then, fewer than 200 people have been infected, but more than half of these human victims have died. Now, the deadly virus is spreading among birds in country after country, raising the fear factor for humans, too. How can a disease that afflicts birds threaten people? What can you do to protect yourself?. Science World asked leading scientists to give you the answers you need.

Q: What is bird flu?

A: Bird flu, or avian influenza, is a disease caused by a virus. Viruses are tiny, nonliving particles that invade and then reproduce inside of living cells. Many flu viruses exist, but the one causing the worldwide stir is H5N1. The two letters in this code name stand for the two proteins, or strings of chemicals called amino acids, that form the virus's coating: Hemagglutinin and Neuraminidase. The number to the right of each letter indicates which version of the protein the coating contains.

Like all flu viruses, H5N1 started in wild water birds. In 1959, scientists first spotted the virus in ducks. Since then, the disease-fighting immune systems of these wild birds have adapted to mount a defense against H5N1. So today, many infected wild birds seem healthy. But when these birds migrate, they carry the virus to new areas of the globe. There, they spread H5N1 to other species through their saliva, feces, and nasal secretions.

Unlike wild birds, domesticated birds such as chickens aren't used to H5N1. So when they come in contact with the virus, their immune systems aren't prepared for the attack and the birds become sick quickly. "H5N1 viruses grow so rapidly [in chickens] after infection that they spread to multiple organs, such as the lungs and brain," says Erich Hoffmann, a virologist at St. Jude Children's Research Hospital in Tennessee. Tens of millions of infected chickens have either died from the disease or been purposely destroyed by people to stop the spread of H5N1. The risk to domesticated birds from H5N1 is greatest in places such as Africa and Asia, where many poultry are kept in open-air, backyard flocks and can easily mingle with infected wild birds.

Q: How is bird flu different from human flu viruses?

A: Seasonal human flu viruses also came from birds, but these viruses have existed for many years. Over time, the human immune system has developed defenses against them. Even though these viruses are nothing to sneeze at--especially for the very young, the elderly, and those already weakened by illness--most infected people recover.

But H5N1 is new to humans, so your immune system hasn't been primed to protect you. Joseph Bresee, an influenza expert at the Centers for Disease Control and Prevention, says, "[H5N1] has the potential to cause more severe diseases because people haven't been exposed to a flu virus that looks like this before."

With the immune system caught off guard, H5N1 can be lethal even to people in peak health. When first infected, victims experience normal flu symptoms like fever and headache, but in a few days they develop pneumonia, an inflammation in which the lungs fill with fluid. "Basically, the patient suffocates," Hoffmann says.

The good news: People who aren't working closely with infected birds don't have much to fear. "For the most part, the people who have come down with this bird flu have been in long, sustained contact with the feces and respiratory secretions of infected birds," says John El-Attrache, an avian virologist at Texas A&M University.

In addition, H5N1 doesn't spread easily from human to human, which is why there have been so few human cases. Other flu viruses multiply in the upper respiratory tract, where they're spread by coughing and sneezing. But new studies show that H5N1 multiplies only deep in the lungs of infected humans, where it won't be spread to others. But this could change.

Q: What needs to happen for H5N1 to spread easily from person to person?

A: H5N1 multiplies by hijacking healthy cells and directing them to make copies of the virus. "Each time the [virus] copies itself, there's a chance for mistakes to occur," says Bresee. These mutations are usually small. But scientists worry that the right series of genetic mistakes could give H5N1 the ability to spread easily among humans.

Another concern: If a person catches a human flu and H5N1 at the same time, cells copying both viruses could mix them together (see Nuts & Bolts, p. 18). This reassortment could result in a combination virus that has the human flu's ability to spread and the bird flu's ability to kill. Mutations or reassortment could trigger a pandemic, or global outbreak.

Q: How would scientists fight the virus if it were to mutate and become easily contagious among humans?

A: "The best weapons against viruses are vaccines," Hoffmann says. To make a vaccine, scientists grow a known virus, inactivate it so it can't multiply, and inject it into humans. The immune system reacts by producing proteins called antibodies to fight the virus. Later, if the person gets exposed to the active form of that virus, these antibodies will already be in place to eliminate the invader, and the person won't become infected.

Each flu virus requires a different vaccine. Unfortunately, no one knows how H5N1 might change to become a pandemic virus. So the best that scientists can do ahead of time is make a vaccine that they suppose would be a close match to the pandemic virus. If a pandemic were to occur, the options would be to use this stockpiled--though possibly "suboptimal"--vaccine or to develop a vaccine from scratch, which could take months.

Q: What's being done to keep people safe?

A: Scientists are looking for faster methods to make new vaccines, and they're recommending that governments stockpile antiviral medicines.

With the world on alert, the deadly virus won't slip under the radar. Bresee says the best way for Americans to stay safe is to pay attention to the news. "If we think there is a risk of anybody in the United States getting avian influenza, we'll tell them how to protect themselves."

Far From a First

Bird flu isn't the first disease to jump from animals to humans. Experts believe that most infectious human diseases came from our feathered and four-footed friends.

The famous plague, or "Black Death," that killed one third of Europe's population in the 14th century came from rats infested with infected fleas.

Other culprits are goats, which are thought to have spread tuberculosis (TB) to humans, and pigs, believed to have been carriers of whooping cough. Once TB and whooping cough spread to humans, the bacteria that cause these diseases mutated. Those changes allowed the diseases to spread easily from human to human.

Scientists think cows were probably the source of viruses that mutated to cause measles and smallpox in humans. But cows also helped bring vaccines to the world. In 1796, an English doctor discovered that patients who had recovered from a cattle disease called cowpox were immune to the more dangerous smallpox. People began to "vaccinate" themselves by catching cowpox on purpose.

nuts & bolts

The bird flu virus has similar structure to a human flu virus. If a person already infected with human flu catches bird flu, the two viruses could combine inside the person's body, possibly forming a new virus.

The result would be a virus that contains genetic material from each flu virus. Such a strain could spread easily among humans.

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web extra

Although these is currently no pandemic flu, government-issued checklist helps schools to be prepared:

www.pandemicflu.gov/

plan/schoolchecklist.html

PREVENTION: In an attempt to stop the spread of the deadly H5N1 virus (inset, gold), workers in Iran had to collect and destroy infected birds.

AUTOPSY: A veterinarian tests this dead swan for H5N1.

BURIAL: To avoid spread of the virus, officials bury bags full of dead chickens in South Korea.

PRE-READING PROMPTS

Jumpstart your lesson with these pre-reading questions:

* In October 2004, 441 captive tigers in a zoo in Thailand were fed raw chicken meat. A portion of the meat turned out to have been infected with the avian influenza virus H5N1. As a result, 147 of the tigers died or had to be killed because of bird-flu infection. Investigation suggests that some of the tigers contracted H5N1 when they ate the infected chicken meat. The other tigers caught the virus front the infected tigers. How do you think humans contract bird flu? And how do humans transmit the virus to one another?

* Vaccines can protect humans from many viruses such as the chicken pox, measles, and polio. As of now, humans can't be vaccinated against the avian influenza virus. What do you think is the reason?

CRITICAL THINKING

* If H5N1 mutates into a virus that spreads easily among humans, how might people protect themselves front catching the virus? Come up with five precautionary measures for your school and five more for your home.

CROSS-CURRICULAR CONNECTIONS

GEOGRAPHY: Give each student a world map. Then have them study the time line of the avian influenza outbreak on this World Health Organization Web site: www.who.int/csr/disease/avian_influenza/Timeline_15.02.pdf. Using the information in the time line, have each student track the spread of bird flu on his or her map. For each case of outbreak, place a mark on the country in which it was discovered. (Note: To separate an avian infection front a human case, be sure to use different marks.) Then label the mark with the month and year of the outbreak.

RESOURCES

* For diagrams, facts, and articles about avian influenza, visit this Web site from The New York Times: http://topics.nytimes.com/top/news/health/ diseasesconditionsandhealthtopics/ avianinfluenza/index.html

* The Centers for Disease Control and Prevention has the latest news and information about bird flu. Visit their Web site at: www.cdc.gov/flu/avian/

* For teen-friendly explanations on the basics of bird flu, go to: www.kidshealth.org/kid/health_problems/infection/bird_flu.html

CHECK FOR UNDERSTANDING

Name: --

DIRECTIONS: On a separate piece of paper, answer the following questions in complete sentences.

1. What is H5N1 and what do the letters and numbers stand for?

2. Why don't many wild birds infected with H5N1 seem sick?

3. How do infected wild birds spread H5N1 to chickens? And why do chickens get sick from it so easily?

4. How do vaccines work?

5. What infectious human diseases are believed to have originated from rats, goats, pigs, and cows?

ANSWERS

Bird Flu

1. H5N1 is the code name for the avian influenza virus that is causing worldwide alarm. The two letters in the name stand for the two proteins that form the virus's coating: Hemagglutinin and Neuraminidase The number to the right of each letter indicates which version of the protein the coating contains.

2. In 1959, scientists first spotted the H5N1 virus in ducks. Since then, the disease fighting immune systems of these wild birds have adapted to mount a defense against H5N1 So many infected wild birds don't seem sick.

3. When infected wild birds migrate, they carry H5N1 to new areas of the globe There, they spread the virus to other species through their saliva, feces, and nasal secretions, Since domesticated birds such as chickens aren't used to H5N1, their immune systems aren't prepared for the attack. When these birds catch the virus, they become sick quickly.

4. To make a vaccine, scientists grow a known virus, inactivate it so it can't multiply, and inject it into humans. The immune system reacts by producing antibodies to fight the virus. Later, if the person gets exposed to the active virus, these antibodies will already be in place to eliminate the invader, and the person won't become infected.

5. The plague, or "Black Death," came from rats infested with infected fleas Goats are thought to have spread tuberculosis to humans. Pigs are believed to have been the carriers of whooping cough. Scientists also think cows were probably the source of viruses that mutated to cause measles and smallpox in humans.