The Threat of Bird Flu

 

 

 

The Threat of Bird Flu    

 

You may have recently been hearing about “bird flu,” but do you know what it is? Many people 

don’t. Basically, the influenza virus comes in three general varieties; A, B and C. These reflect 

differences in the M protein on the envelope that contains the virus. The A influenza viruses are the 

ones that cause both human and bird flu outbreaks. Each virus contains an RNA strand that has eight 

segments. These segments break apart during replication and can mix and re-assort with other 

segments. The potential for constant evolution of these viruses is therefore built into the system.1 

 

Type A influenza viruses are sub-typed based on two different kinds of activity within their 

envelope’s glycoproteins. The first is hemagglutinin activity, designated H. There are 16 known 

varieties of this. The second is neuraminidase activity, designated N, with nine known varieties. The 

shorthand code names of both bird and human flu always have an “H” and “N” number. For example, 

the 1918 Spanish flu pandemic was caused by H1N1.1,2,3 

 

Bird flu and human flu have a complex and likely inter-related story. The three influenza A 

viruses associated with the 20th century human pandemics all appear to have genetic components 

originally housed in viruses in birds. The 1918 H1N1 virus killed 20 to 40 million people worldwide. 

The 1957 H2N2 and 1968 H3N2 viruses were far less lethal, but still were each responsible for more 

than 1 million deaths.3 Now, in 2005, all eyes are focused on H5N1, more commonly known as bird 

flu.4   

 

The influenza A virus appears most in wild bird populations, spreading rapidly through 

exchange of mucus or feces, and generally without creating sickness or death in these species.2 

However, once it transfers over to domestic birds, including chickens, ducks and turkeys, it spreads 

explosively and is frequently lethal. In large groups of closely contained birds, the virus mutates 

rapidly and also has the ability to jump to other species such as pigs. These secondary carriers 

become mixing pots for even more varieties, greatly increasing the chances that other mammals, 

including humans, will become vulnerable.5 

 

The H5N1 bird flu has infected humans and continues, as we speak, to evolve.6 It was first 

identified in South African wild terns in 1961.2 It spread naturally throughout global bird populations 

over the next four decades, appearing dramatically in poultry populations in 2003. That outbreak 

occurred in eight countries in Asia – Cambodia, China, Indonesia, Japan, Laos, South Korea, 

Thailand and Vietnam – and resulted in the loss of more than 100 million domestic birds. The 

outbreak appeared under control until June of 2004 when it reappeared in four of the same countries 

and Malaysia.1.2. 

 

In humans, the appearance was less dramatic. H5N1 first infected a human population in Hong 

Kong in 1997. There were 18 documented cases and six deaths. It reappeared in 2 cases, causing 

one death in 2003, but shortly thereafter broke out in Vietnam, Thailand and Cambodia. As of June 

 

2005, there were 100 documented human cases with a 54 percent mortality rate. Most transmission 

has been the result of direct contact with infected poultry.1,2   

 

But 100 deaths does not a pandemic make. You need three things for a pandemic. First, a 

highly virulent organism. Second, lack of human immunity to the organism. And third, the ability for 

easy transmission from human to human.3 In 1918, H1N1 had all three. That’s why 20 to 40 million 

people died. In 2005, H5N1 has the first two, but not the third – at least not yet. 

 

But concerns are high. For one thing, studies demonstrate continued evolution.3 In response, 

the host range of H5N1 is expanding and is now present in pigs, horses, cats, tigers, leopards, 

whales and seals.1 This, in part, has been made possible by the tremendous expansion of the 

domestic bird population in Asia. In China alone since the last pandemic outbreak in 1969, the 

number of domestic chickens has increased from 8 million to 13 billion.6 The number of domestic pigs 

has also increased. Pigs, in particular, are viewed as a catalytic mixer of genetic brews. Finally, 

human-to-human transmission has occurred in a documented case of child to mother to aunt in 

Thailand.7 But the spread stopped there, suggesting that the virus does not yet have the capability to 

readily jump from one human to the next. 

 

Our current capacity to diagnose and manage an H5N1 pandemic is less than adequate.8 To 

prevail, we need excellent surveillance that relies on clinical, scientific and technologic capacity. We 

need knowledge sharing and the will to act, and act quickly, at the first signs of facilitated human-to- 

human transmission. Specific concerns are that H5N1 is already resistant to two of four common anti- 

viral drugs.2 Our supply of the two non-resistant drugs is woefully inadequate for a worldwide 

epidemic.8 But there is some good news – on Aug. 7, health officials announced success in an initial 

test of a human vaccine. They cautioned, however, that the existence of a vaccine in itself would not 

be enough to prevent a worldwide pandemic. They said more testing must be done before the 

vaccine can be offered to the public, and production could be a stumbling block. Because the vaccine 

is made in chicken eggs, successful mass production is dependent upon the numbers of eggs 

available. Other obstacles to consider include an organizational system for distribution of the vaccine 

once it becomes available.9,10  

 

Managing the real risk of bird flu requires global cooperation, expanded surveillance, and 

expanded capacity. We need to track H5N1 worldwide, agree on a research plan, share knowledge, 

and be ready to intervene. With poultry, that means proactive surveillance of all subtypes, modifying 

production and distribution, and strict enforcement. For humans, we need broad surveillance and 

detection, cluster investigation, contact tracking, targeted use of anti-virals, continued vaccine 

research and development, and travel restrictions when appropriate.  

 

Human transmission of bird flu is predictable and therefore manageable. Failure to take action 

could be a mistake of historic proportions. 

 

For Health Politics, I’m Mike Magee. 

 

 

References 

 

1. Infectious Diseases Society of America Web site. Avian Influenza (Bird Flu): Implications for 

Human Disease. Available at: 

http://www.cidrap.umn.edu/idsa/influenza/avianflu/biofacts/avflu_human.html. Accessed Aug. 

19, 2005. 

2. Centers for Disease Control and Prevention Web site. Information about Avian Influenza (Bird 

Flue) and Avian Influenza A (H5N1) Virus. Available at: http://www.cdc.gov/flu/avian/gen- 

info/facts.htm. Accessed Aug. 19, 2005. 

3. Hien TT. De Jong M, Farrar J. Avian influenza – a challenge to global health care structures. 

NEJM. 2004;351:2363-2365. 

4. Hastings M, Guteri F. Bird-Flu Challenge. MSNBC.com. Dec. 13, 2004. 

5. Fouchier R, Kuiken T, Rimmelzwaan G, Osterhaus A. Global task force for influenza. Nature. 

2005;435:419-420. 

6. WNYC. The Leonard Lopate Show. Underreported: Avian Flu. July 14, 2005. 

7. Ungchusak K, Auewarakul P, Dowell SF, Kitphati R, Auwanit W, et al. Probable person-to- 

person transmission of avian influenza A (H5N1). NEJM. 2005;352:333-340. 

8. World Health Organization. Report by the Secretariat. Avian influenza and human health. April 

8, 2004. 

9. Altman LK. Avian Flu Vaccine Called Effective in Human Testing. The New York Times. Aug. 

7, 2005. 

10.  Altman LK, Bradsher K. A Successful Vaccine Alone Is Not Enough to Prevent Avian Flu 

Epidemic. The New York Times. Aug. 8, 2005.