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| Author: | Carin Zissis |
|---|
November 21, 2006
Global public health organizations and researchers have spent the past few years monitoring a highly pathogenic type of avian influenza that originated in Southeast Asia. Hundreds of millions of chickens have succumbed to the virus, and the world is worried humans may be next if the flu evolves to allow human-to-human transmission. So far, the number of human cases grows slowly each year, but a virus mutation could set off a pandemic. For public health researchers and policymakers, questions about how the disease spreads, as well as how to treat and control it, remain unanswered.
“Bird flu,” as it is more commonly known, is a highly contagious virus that spreads among birds, particularly poultry, and passes from one geographic region to another through migration of the natural host species—aquatic ducks and geese—as well as by animal smuggling. The virus does not affect humans on a large scale. To date, human instances of the virus are largely a result of contact with infected birds. However, if a strain of the virus evolves that can be transferred easily from one person to another, experts fear it could spread rapidly into a global health threat and prove exceptionally difficult to contain. In this dark scenario, avian flu could lead to a lethal pandemic if a deadly strain were to emerge.
Experts note that the influenza pandemic of 1918 was a form of avian flu that killed as many as fifty million people worldwide. Now, they warn, action is needed to prevent a similar pandemic based on an avian flu subtype known as H5N1. This bird flu, first identified in Hong Kong, has claimed more than 150 lives, primarily through contact with infected poultry.
Aside from the potential widespread danger to human health, avian flu poses global economic risks in terms of trade and containment costs. After a subtype of lethal avian flu infected eighteen people and killed six in Hong Kong in 1997, the island’s chicken population—about 1.5 million birds—had to be slaughtered. In 1983, a milder form of bird flu infected poultry in Pennsylvania, forcing the culling of seventeen million chickens. The World Bank estimates that a serious avian flu pandemic could have a global cost of $2 trillion.
Avian flu is highly contagious among chickens and can spread from farm to farm by the transfer of poultry as well as through pathogens on people’s clothing, contaminated vehicles, feed, equipment, and cages. An increased chance of transmission exists in situations where farmers have backyard flocks that roam freely and share water with migrating birds.
Highly pathogenic bird flu can lead to death in poultry within forty-eight hours. The disease affects the respiratory tract, but has been dubbed “chicken Ebola” because of its ability to cause massive internal hemorrhaging. However, the virus is not harmful to migratory birds such as aquatic ducks and geese, which can carry the disease while bearing little signs of illness. Laurie Garrett, CFR senior fellow for global health, says smuggled animals—typically expensive breeding birds—infected with H5N1 have brought the disease to northern Africa and perhaps to the Middle East, as well as from region to region in Turkey. She explains the virus can “jump great distances,” as from China to Siberia or Siberia to Romania, when migrating birds spread the disease.
Beginning in 2003, outbreaks of avian flu in birds in Southeast Asia spread to South Korea, Vietnam, Japan, Thailand, Cambodia, Laos, North Korea, Indonesia, China, and Malaysia. Since then Japan, South Korea, and Malaysia have eradicated the disease. But the disease has since been detected beyond Asia in the Middle East, Africa, and Europe. Even though outbreaks can be controlled, the recurrence of migration contributes to the likelihood of future outbreaks.
A highly pathogenic form of avian flu has not yet been detected in the Americas, most likely because of the general separation of established migration air routes, or flyways, and, says Garrett, “the strange patterns of global bird smuggling” limit the chance for infected birds’ arrival. But, she warns, “I can not imagine how this part of the world will remain uninfected,” given that there is an existing overlap in migration routes between previously infected areas andAlaska. The large-scale containment and separation of birds in the American poultry industry could help prevent interaction with and exposure to infected migrating birds in the United States.
That’s not to say the U.S. poultry industry feels immune. Corporate information about avian flu seeks to calm fears among U.S. consumers and is prominently displayed on the websites of major poultry producers like Tyson Foods and Perdue Farms. The fastest-growing market for poultry in the United States is in “free range” chickens, which would be more vulnerable to infection. If the disease reached Latin America, where larger numbers of backyard, free-roaming chickens exist, its spread would be difficult to control.
Yes, although the rate of contagion currently appears limited. Hundreds of millions of poultry have been infected by the disease in recent years, yet fewer than 300 human cases have been reported. Still, since 2003 the number of deaths associated with bird flu has increased annually. 2006 is already the most lethal year, with over seventy reported avian flu deaths.
Most bird flu cases have occurred in poor rural areas and in households with small poultry flocks where the chickens may roam in and out of homes. In a few cases, the disease has passed from one person to another in Southeast Asian countries, but the virus lacks the capacity to spread easily from human to human. Scientists recently identified the genetic factors missing from the virus that they believe are necessary for rapid transmission among humans. Close contact with sick birds, such as butchering them or exposure to pathogens in feces, appears to be the primary cause of infection. But there have been few reported cases among presumably high-risk groups such as poultry workers, veterinarians, and healthcare workers handling infected patients without protective gear.
For bird flu patients, early symptoms include fever and other flu-like symptoms, as well as respiratory distress and pneumonia. The disease has a high mortality rate—in roughly 60 percent of documented cases people died—and a patient can die within days. When illness is detected early enough, an antiviral drug called Tamiflu can increase a bird flu victim’s survival chances.
Since 2003, confirmed human cases of avian flu have occurred in Djibouti, Egypt, Azerbaijan, Turkey, and Iraq, although the countries with the highest case counts are Vietnam, China, Thailand, and Indonesia. Garrett says there are also “constant rumors” of bird flu in Iran, but lack of transparency limits gaining more information about the extent of outbreaks there.
There are means to attempt to limit bird flu outbreaks, although the weakness of some of the control methods and the evolution of the virus present obstacles to its management.
In September 2005, the Bush administration announced the launch of the International Partnership on Avian and Pandemic Influenza at a UN General Assembly meeting. Since then, the United States has committed the largest share of a global pact to raise $1.9 billion for helping developing countries handle avian flu. With the involvement of the State Department, the United States now trains scientists and health workers in South Asia. Although more work needs to be done globally, there has been a great deal of progress in terms of policy, says Garrett. “We will, as a global community, be in a better position to limit our losses, maintain global order, and come up with reasonably equitable ways to distribute whatever supplies we do have than we would have been two years ago.”
Experts are not sure if and when avian flu might evolve to become more easily transmittable from one human to another. But the World Health Organization warns pandemics are recurring; although the pandemic of 1918 was the deadliest in the past century, the subsequent one in 1957 claimed two million lives. Morse says the relatively mild pandemic of 1968, when one million people died globally, “caused complacency. I think we have complacency until something happens, and then we panic.” Such panic would likely be set off by widespread illness, inadequate medical supplies, and widespread death across borders. Says Garrett, “Flu is by far the most contagious probability in our near horizon, and there are no fools left who think you can confine it to one country and keep it from spreading around the world.”
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