What is pandemic influenza?
Pandemic influenza is a global outbreak of disease from a new influenza type A virus to which most or all people will not have any natural immunity (protection).
Is a pandemic expected?
Pandemic influenza occurs naturally. There were three pandemics in the 20th century. The pandemic of 1989-1919 was the most severe pandemic on record, in which approximately 650,000 Americans died. It is not possible to accurately predict when pandemic influenza will occur or how severe it will be. However, the current outbreak of Influenza H5N1 (avian flu) in Asia has experts concerned that a pandemic is developing.
What is avian influenza?
Avian influenza or "bird flu," is a contagious viral disease that normally infects only birds and on occasion, pigs. A highly pathogenic strain, H5N1, has been persistent and tenacious. Despite the fact that an estimated 250 million birds have died or been destroyed, the virus has become endemic in some areas and may be spread by migratory birds.
Which countries have been affected?
Outbreaks in wild and domestic birds have been reported in more than 40 countries including: the Republic of Korea, Vietnam, Japan, Thailand, Cambodia, Loa People Democratic Republic, Indonesia, China, Malaysia, Mongolia, Russia, Kazakhstan, Turkey, and Romania.
What are the implications for human health?
Widespread persistence of H5N1 in poultry populations poses two main risks for human health. The first is the direct infection from poultry to humans. The second threat is the emergency of a mutant strain that spreads easily from person to person.
How is the virus transmitted?
The bird to human transmission occurs from direct contact with infected poultry or surfaces and objects contaminated by their feces. Exposure to the virus is most likely during slaughter, de-feathering, butchering, and preparing poultry for cooking. Currently, there is no evidence that properly cooked poultry or eggs are a source of infection.
What changes are needed for the H5N1 virus to affect humans and become pandemic?
The virus can become transmissible among humans by either a "reassortment" event or by a more gradual process of adaptive mutation.
In "reassortment" genetic material is exchanged between human and avian viruses when there is co-infection in a human or pig. This results in a new potent strain that is fully transmissible to humans. The process of adaptive mutation is a more gradual process by which the virus becomes more efficient at binding to human cells.
A pandemic can start when three conditions have been met: a new virus subtype emerges; it infects humans; and it spreads easily and is sustained among humans.
The first two conditions have been met in that a new subtype has emerged and humans have been infected through contact with infected birds.
Are vaccines and antivirals available for prevention and treatment:
Some vaccine clinical trials are currently underway. Because the antigen needs to closely match the pandemic virus, large-scale production will not start until the virus has emerged. Current vaccine production capacity cannot meet demand.
Tamiflu and Relenza are oral antivirals that are currently available and are effective for reducing the severity and duration of the illness. These medications can also be used prophylactically to decrease the number of new cases when an exposure has occurred.
Will the regular annual influenza shot provide any protection against the pandemic influenza virus?
Probably not. But the regular influenza shot will protect you against the influenza viruses that are circulating right now.
References:
World Health Organization www.who.int/csr/disease/avian_influenza
Centers for Disease Control www.cdc.gov/flu/avian
from a publication by the American College Health Association