What is avian influenza?
Avian influenza, or “bird flu,” is a contagious disease caused by one of a class of viruses that normally infect only birds. Why is it such a concern?
Because sometimes avian influenza viruses can cross the species barrier, infecting humans and spreading from person to person. Prior global pandemics originated when bird influenza viruses jumped directly into man (as in 1918) or when chimeric bird influenza - human influenza viruses emerged and became transmissible from human to human (as in 1957 and 1968). Can the avian flu virus be transmitted from human to human?
So far, human infections with avian H5 influenza viruses have not started jumping from human to human. There have been some instances of multiple cases in one family, but no evidence of a chain of two or more successive human to human transmissions. Where does the avian flu virus hide between outbreaks?
Wild ducks and shorebirds are the natural reservoir for all influenza A viruses. At any given time, as many as 10 percent to 20 percent of waterfowl may be infected with one or more of the major avian influenza types. Every day, millions of billions of virus particles are silently replicating, swapping genes, mutating and evolving in waterfowl. What does “H5N1” mean?
Influenza virus types are named according to the proteins on their surfaces: The H, or hemagglutinin, protein allows the virus to attach to and enter animal cells, where it replicates. The N, or neuraminidase, protein allows these newly replicated virus particles to exit from a cell and go on to infect others. There are at least 15 known H types and 9 known N types, and these can be present together in any combination. Has H5N1 killed people?
In the last three years, H5N1 viruses have infected more than 275 people and killed 167. (Visit the WHO's avian flu website for the latest accounting of confirmed H5N1 cases worldwide) How severe would an avian flu pandemic be?
It is difficult to speculate. At one extreme, if the 50 percent mortality ratios now seen in Southeast Asia were to be maintained, then the human species might face extinction—but this scenario is unlikely. The 1918 pandemic was exceptionally lethal: 1 percent to 2 percent of infected cases died, killing at least 40 million people worldwide. Even if a new virus were to cause only mild disease, the world could still experience an estimated 2 million to 7 million deaths. Could a worldwide effort stop a pandemic?
Because the influenza virus is spread so rapidly by coughing or sneezing, once a pandemic takes off virtually all countries would be infected within weeks. Thus, if each government had to focus on caring for its own population, the types of inter-country assistance seen during natural disasters or localized disease outbreaks would not happen. On the other hand, computer modeling at the Bloomberg School of avian flu epidemics has shown that it may be possible to avert a pandemic if a human outbreak were identified at its earliest stage—when there are still fewer than 100 cases—and international resources such as a WHO stockpile of antiviral drugs were deployed. Is the world adequately prepared?
Not really. Vaccines effective against a pandemic virus are not yet available. WHO has urged all countries to develop preparedness plans, but only about 40 have done so. Around 30 developed countries are trying to purchase large quantities of antiviral drugs, but the manufacturer has no capacity to fill these orders immediately. Most developing countries will have no access to vaccines and antiviral drugs throughout the duration of a pandemic. What is the status of vaccine development?
The vaccines produced each year for seasonal influenza will not protect against a new pandemic influenza strain. Although a vaccine against the H5N1 virus is under development in several countries, no vaccine is ready for commercial production and, because the vaccine needs to closely match the pandemic virus, large-scale commercial production will not start until the new virus has emerged and a pandemic has been declared. Current global production capacity falls far short of the demand expected during a pandemic. Is it safe to eat poultry and poultry products?
In areas free of the disease, poultry and poultry products can be prepared and consumed as usual. In areas experiencing outbreaks, poultry and poultry products can also be safely consumed provided these items are properly cooked and properly handled during preparation. What drugs are available for treatment?
Two drugs that inhibit neuraminidase—Tamiflu and Relenza—can reduce the severity and duration of illness caused by seasonal influenza. The efficacy of the neuraminidase inhibitors depends on their administration as quickly as possible after symptom onset. The H5N1 virus is expected to be susceptible to the neuraminidase inhibitors, so these drugs may improve prospects of survival if administered early, but clinical data are limited. Influenza virus resistance to these drugs could emerge to be a serious problem. The main drawbacks for these drugs are scarcity and a price that is prohibitively high for many countries. Present manufacturing capacity has recently quadrupled, but it will take a decade to produce enough Tamiflu to treat 20 percent of the world’s population. Public Affairs media contacts for the Johns Hopkins Bloomberg School of Public Health: Tim Parsons or Kenna Lowe at 410-955-6878 or paffairs@jhsph.edu. | 
