The Avian Influenza Pandemic: If Not Now, When?
Avian influenza was the hottest topic in infectious disease in 2005. Transmission of the virus from birds to humans caused 139 cases of the human disease, including 71 deaths, as of December 15, 2005, according to the World Health Organization (WHO).
Although human-to-human transmission has not yet been documented, the virus is theoretically capable of mutating to do just that. How worried should we be?
Judging by sales of Roche's Tamiflu, some people are very worried indeed. Global concerns about the disease have reportedly prompted stockpiling of Tamiflu by governments, doctors and individuals. One story in October 2005 noted that eBay UK stopped an auction of Tamiflu on its site when prices jumped above US$174.
Whom to believe? Following is a brief background on Bird Flu, along with highlights from 2005 news reports on the potential for a pandemic.
Origin of Avian Influenza
Avian influenza - also known as "Bird Flu" - is caused by a type of virus hosted by birds, although it may in fact be present in a variety of mammals, too. First identified in Italy in the early 1900s, the virus has now been found in many countries.
The virus has several subtypes. One subtype -called "H5N1" - was first identified in humans in 1997 in Hong Kong. Bird Flu has reemerged in China and Southeast Asia since 2003, killing 74 people there, and more recently has appeared in Turkey.
The H5N1 strain has been identified by the WHO as the likely source of a future influenza pandemic. Of primary concern is that the virus could spread rapidly across countries, along the migration routes of birds.
Treating Avian Influenza: Tamiflu & Other Antivirals
Tamiflu (oseltamivir) is an anti-viral agent designed to fight human influenza. Tests show it may be effective in decreasing the severity of illness and complications caused by the H5N1 strain of avian influenza, if taken in higher doses.
Although Tamiflu is currently the most widely known treatment for avian influenza, reports suggest that other antiviral drugs - specifically, zanamivir (brand name Relenza) and amantadine (brand name Symmetrel) - may also effectively prevent and treat the disease.
However, widespread use of amantadine on chickens in China, starting in the late 1990s, has caused some strains of avian influenza virus to become resistant to amantadine. For this reason, some reports suggest that countries that have been stockpiling Tamiflu may benefit from shifting towards stocking zanamivir.
- Case of Bird Flu Resistance, BBC News, October 14, 2005
According to the Centers for Disease Control and Prevention (CDC), the H5N1 virus is resistant to amantadine and rimantadine, but would likely respond to treatment with either oseltamivir or zanamavir. However, the CDC notes that additional studies are required to confirm these drugs' efficacy in treating people infected with the virus.
Further complicating the issue of treatment is a recent report that people in Vietnam have died of avian influenza, despite receiving treatment with oseltamivir. The study,
- Scientists in uphill battle to fight bird flu, Reuters, January 6, 2006
WHO reports and updates on avian influenza treatment issues can be found here:
- Vaccine research and development: current status
- Antiviral drugs: their role during a pandemic
- Non-pharmaceutical interventions: their role in reducing transmission and spread
Likelihood of a Pandemic
According to the WHO, the current status of the much heralded avian influenza pandemic is still relatively low, rating "3" on the WHO's own scale, which is defined as "no or very limited human-to-human transmission".
Mutation of the virus to a form that would permit human-to-human contact would be the leading factor in creating a pandemic. While some experts feel that the mutation may be inevitable, given the aggressively mercurial nature of viruses, thus far human-to-human transmission has not been documented.
To date, the WHO has not recommended any restrictions to travel to areas affected by avian influenza, or screening of travelers from these areas. However, they do recommend that people avoid contact with high-risk environments in affected areas, and that they exercise caution to ensure that all poultry products are properly cooked and not at risk of cross-contamination:
- WHO recommendations relating to travellers coming from and going to countries experiencing outbreaks of highly pathogenic H5N1 avian influenza
- Food safety issues
The WHO's "Situation Updates" page and others provide regular news updates on outbreaks of avian influenza- where they happen and when:
- Confirmed Human Cases of Avian Influenza A(H5N1)
- OIE updates on avian influenza situation in birds
- FAO animal health special report
Avian Influenza: 2005 News Reports
Drugs.com Articles on Tamiflu:
- U.S. Food and Drug Administration Extends Prophylaxis Indication for Tamiflu to Children Between One to 12 Years of Age, December 21, 2005
- Tamiflu Deemed Safe After Death Reports, November 23, 2005
- Probenecid: Makes Tamiflu Last Longer, November 7, 2005
- Avian Flu Resistance to Tamiflu (oseltamivir) Antiviral, October 4, 2005
Avian Influenza Research:
- UK scientists to reveal gene code of bird flu in days, January 10, 2006
- Bird flu spreads to humans more easily than thought, January 9, 2006
- Bird Flu May Be More Common, Less Deadly, January 9, 2006
- Â£10m bird flu research announced, November 30, 2005
- International Team Issues Avian Flu Recommendations, September 28, 2005
- Avian Flu Vaccine Produces Immune Response, August 8, 2005
- Flu Research Clarifies Secrets of Past Pandemics, October 5, 2005
- Star Anise Spice: New Treatment for Bird Flu? November 30, 2005
Additional ResourcesFor more information on avian influenza and the potential pandemic, visit:
- WHO Epidemic and Pandemic Alert and Response
- National Institutes of Health-Medline Plus Bird Flu Information
- MayoClinic.com -Bird Flu
Avian Influenza, Wikipedia.org.
Key Facts About Avian Influenza (Bird Flu) and Avian Influenza A (H5N1) Virus, Centers for Disease Control and Prevention.
Oseltamivir Resistance during Treatment of Influenza A (H5N1) Infection. Menno D de Jong, MD, PhD, The New England Journal of Medicine, volume 353(25), pages 2667-2672, December 22, 2005.
WHO Epidemic and Pandemic Alert and Response
Posted: December 2005