Bird Flu
Bird flu, also known as avian influenza A, is a contagious disease of migratory and domestic birds. As a “zoonotic” virus, or animal virus that has crossed species to infect humans, it has been reported in about 400 cases of human infections since 2003 worldwide.All influenza viruses are named according to two surface molecules: hemagglutinin (HA or H) and neuraminidase (NA or N). H5N1 is the highly pathogenic form of the bird flu that has caused recent outbreaks in birds in Asia, Europe, Africa, and the Near East. H5N1 has caused infections of more than 100 million birds, as well as in a growing number of people.
Definition of Pandemic
According to the World Health Organization (WHO), a pandemic (or global disease outbreak) has to meet three conditions:
- The virus infects and causes serious illness in humans.
- Humans do not have immunity against the virus.
- The virus spreads easily from person-to-person and survives within humans.
Risk for Bird Flu Pandemic
The current H5N1 bird flu virus meets the first two criteria of the pandemic definition. Only a few cases of person-to-person transmission have been reported (mostly between close family members who are also exposed to the same animal and environmental sources), but health authorities are very concerned about the risk for a flu pandemic. If the bird flu virus mutates to improve its transmission to humans, it could become a very deadly problem.
The WHO is concerned for several reasons. First, the virus has been rapidly mutating to the degree that some domestic ducks can act as a “silent reservoir,” excreting the virus without showing symptoms of the disease. In addition, the virus has evolved in recent years to infect more species of mammals, to become more lethal (causing unusually high rates of deaths in migratory birds), and to survive longer in the environment than previously reported.
Warning Signals of a Bird Flu Pandemic
Human-to-human transmission will result in clusters of people who get infected, as well as an increase in the number of healthcare workers who get infected by their patients. These events are being closely monitored by government agencies in order to determine whether human-to-human transmission is occurring.
Bird Flu Vaccine
No vaccines are currently available for H5N1, but clinical trials of experimental vaccines are ongoing. Development of a vaccine for H5N1 is challenging because the virus will mutate to some degree before it can cause human-to-human transmission. Until an actual pandemic virus emerges, it is unknown how effective the currently researched vaccines will be.
Bird Flu Drugs
The CDC and WHO recommend the prescription antiviral drug Tamiflu (oseltamivir) for treating and preventing human infections with the bird flu virus. Another drug, Relenza (zanamivir) can also reduce severity and duration of human influenza, and may be an option for treatment of bird flu. However, antiviral resistance has occurred in some bird flu viruses, and monitoring of these events by government agencies is critical and ongoing.
Bird Flu Pandemic Prevention
Prevention of a bird flu pandemic is challenging, because the virus would probably need to be eliminated from birds -- an unlikely achievement, since many birds can carry weaker bird flu viruses without showing symptoms. These weaker viruses are believed to mutate into stronger viruses during transmission to domestic birds.
The WHO is stockpiling antiviral medications that may be used as a preventive measure should a pandemic occur. In theory, early prophylactic treatment would delay global spread of the virus and allow additional time to develop and produce adequate vaccines.
Sources Avian Influenza (Bird Flu). Centers for Disease Control and Prevention.
Avian Influenza. World Health Organization.
