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Avian flu: Risks, reality, possibilities
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| Treatment tents: This May 29, 1919 photograph showed rows of tents that had been set up on a lawn at Emery Hill in Lawrence, Mass., where victims of the 1918 influenza pandemic were treated. Courtesy CDC. |
1. What is avian flu?
Of the three types - A, B, and C - of influenza viruses currently circulating, all type A influenza viruses have an avian origin. That is, they originally came from birds. There are at least 16 subtypes of influenza A. Thus far, only subtypes 1, 2 and 3 have acquired the ability to spread from person-to-person in human populations. Recently, some persons have been infected with subtype 5, called H5N1, after contact with sick birds – usually chickens. Subtype 7, called H7N7, has also infected workers in chicken farms in the Netherlands. This virus was the first influenza virus ever recovered and it was originally called "fowl plague."
2. What does H5N1 mean?
Type A viruses are classified into subtypes by comparing proteins on the surface called antigens. In these viruses, the antigens are called hemagglutinin (H) and neuraminidase (N). H5N1 indicates that the avian flu virus has the H5 hemagglutinin and the N1 neuraminidase. A total of 16 hemagglutinins and nine neuraminidases have been identified. Most of these are found only in birds – particularly the aquatic birds like wild ducks and geese.
Most of the avian viruses are relatively benign and produce little illness in the birds. The H5N1 virus usually causes no illness when infecting the water fowl, but may mutate to a highly virulent form if it infects domestic birds like chickens and turkeys. The virulent form of H5N1 will kill most chickens and turkeys within a short time. A few people in close contact with sick birds have developed illness and about half of these persons have died. Most of these cases have occurred in Southeast Asia. Thus far, spread among humans has not occurred, but the concern is that the virus may mutate to allow easy spread among humans. This would result in a pandemic because most humans would be completely susceptible to this virus.
3. What are the symptoms of avian flu?
The initial symptoms would be similar to any flu with fever, chills, muscle aches, cough and sore throat. The most important consideration would be where the person has been. Those who have traveled where sick birds have been found or who have come into contact with sick birds are most at risk. Of the people who have been known to be infected with H5N1, about half have died of overwhelming pneumonia. Hospitalization, isolation and treatment with antiviral drugs would be in order for suspected cases.
4. Do we have a vaccine yet?
There is currently no FDA-approved vaccine against avian influenza, but studies of candidate vaccines are in progress at Baylor and several other medical centers. Recent studies sponsored by the U.S. National Institute for Allergy and Infectious Diseases have been encouraging but more work needs to be done to develop vaccines that are more effective.
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| Deadly pathogen: This negative stained transmission electron micrograph (TEM) showed recreated 1918 influenza virions that were collected from the supernatant of a 1918-infected Madin-Darby Canine Kidney (MDCK) cell culture 18 hours after infection. Dr. Terrence Tumpey recreated the 1918 influenza virus to identify the characteristics that made this organism such a deadly pathogen. Courtesy CDC/ Dr. Terrence Tumpey/ Cynthia Goldsmith |
5. How dangerous will the virus be if it changes to pass from human-to-human?
Currently, we do not know. We have to assume that it would be very dangerous because everyone would be susceptible to a new virus that had not spread in humans before. That is why world and national health authorities are monitoring the situation so closely and making contingency plans.
6. Do you have to have direct contact with an infected bird to get the avian flu? What kind of contact is the most dangerous?
Direct contact with an infected bird is the most efficient method of transmitting the current virus. Most infections have been in people who had direct contact with infected birds, either dead or alive.
7. Can I get avian flu from handling raw birds that carry the virus?
Thus far, the H5N1 virus has not passed from person-to-person. Persons infected have usually had direct contact with sick birds. If cases are suspected, the patients will be isolated in the hospital like patients with other communicable diseases. Good hygiene is important with regular hand washing, avoiding sick persons and using good etiquette when ill. This includes using a disposable tissue to cover mouth and nose when coughing or sneezing, disposing of the tissue in a waste basket and staying away from crowds when ill.
8. Will FluMist protect against bird flu?
FluMist is a live attenuated influenza virus that has been weakened so that it can be given by nasal spray to healthy persons 5-49 years of age. This is a very effective vaccine against the current human influenza viruses. The attenuated (weakened) parent strains are now being combined with the avian H and N proteins to see if this will make an effective vaccine against avian flu. These tests are now being carried out by NIH.
9. What groups are most at risk?
Everyone will be susceptible to a new pandemic strain. Serious illness will occur in healthy young persons as well as in high risk infants and elderly. In a pandemic, everyone will be recommended to receive vaccine. We need to work now to improve vaccine production so that sufficient vaccine can be prepared and can be delivered in a short period of time.
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