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Bird Flu

  • Chris Woolston, M.S.
  • Posted March 11, 2013

During two years in the 20th century, a deadly strain of influenza , known as the "Spanish flu," spread across the globe, killing anywhere from hundreds of thousands to millions of people. It's been many decades since that outbreak. According to some experts, the world is overdue for another.

Though it seems to have stabilized at the moment, some experts believe that bird flu, or avian flu, might one day be such a pandemic. It's an example of a strain of the flu virus called influenza A -- an H5N1 virus that has jumped from one species (birds) to another (us, and a few other unlucky hosts, including a group of tigers in a zoo).

By March 2011, the bird flu had killed more than 300 people and millions of domesticated birds in more than 50 countries, such as Denmark, Greece, Thailand, and Iran. Infection in people is still rare and the human toll has been small so far. According to the U.S. Centers for Disease Control and Prevention, however, the disease still poses a major public health threat.

"So far, the spread of H5N1 virus from person-to-person has been very rare, limited and unsustained," the CDC notes on its website in 2011. "[But] there is little pre-existing natural immunity to H5N1 virus infection in the human population. If H5N1 viruses gain the ability for efficient and sustained transmission among humans, an influenza pandemic could result, with potentially high rates of illness and death worldwide."

What is bird flu?

Federal health agencies put it simply: Bird flu is an infection caused by avian (bird) viruses. Wild birds around the globe carry these viruses in their intestines, but are rarely sickened by them. For domestic birds like chicken, turkeys, and ducks, however, bird flu can be a killer.

Just like humans, birds can come down with the flu. The illness varies widely in intensity, from mild to deadly. A particularly vicious avian flu virus hit domestic chickens and ducks in several Asian countries in late 2003 and early 2004. Millions of birds have either died from the flu or had to be destroyed to stop the spread of the disease.

Because many families in many parts of the world keep small flocks of chickens and ducks, the outbreak has been both an economic disaster and a threat to human health.

As predicted by a number of scientists, the virus spread outside Asia. The World Health Organization reported more than 500 cases in humans by March 2011, including outbreaks in Egypt, Indonesia, Vietnam, and Thailand, along with some cases in Europe and Africa, although the numbers have not changed much over the last few years.

What are the symptoms of bird flu in humans?

Some symptoms of bird flu in humans are similar to those caused by typical flu: fever, cough, sore throat, and muscle aches. Other symptoms include eye infections, pneumonia, severe respiratory diseases, and life-threatening conditions such as acute respiratory distress.

How does bird flu spread?

The virus is found in the saliva, nasal discharge, and feces of infected birds. Most cases in humans seem to have resulted from contact with infected poultry or surfaces contaminated by bird feces. It's also possible for the virus to spread by drinking contaminated water and getting contaminated bird secretions or feces in your eyes or nose, either from touching them or breathing in contaminated particles.

Why are experts so concerned about bird flu?

Bird flu has two of the key qualities of a global threat: It's both deadly and (among birds) extremely common. Despite concerted efforts to quell it, it's still showing up in poultry. It also spreads faster and more widely than any previous bird flu outbreak, and it can be deadly. The only thing keeping it in check at the moment is that it doesn't spread easily from birds to humans or from humans to humans. Although there have been a few documented instances of transmissions occurring between family members in Indonesia and Thailand, confirmed cases of people catching the bird flu from another person are extremely rare.

Unfortunately, flu viruses have a way of finding new victims. If a bird flu virus mingles with one of the human flu virus strains, the two viruses could swap genetic material. In theory, the bird flu could pick up genes that make it as contagious as a strain of flu bug that strikes seasonally. One other way the virus could become more likely to infect people could be through gradual genetic changes over time. The virus has shown that it can infect animals that usually do not get the flu, such as cats. In 2004, 147 tigers at a single zoo in Thailand were killed after 45 died and the rest developed severe cases of bird flu, presumably after eating infected chickens. And in Germany and Austria, domestic cats have been infected with the virus.

If the virus does start spreading quickly to people, it could turn into a major killer. Humans have very little natural immunity to the bird flu. To make matters worse, viral resistance may render two common antiviral flu medications -- amantadine and rimantidine -- ineffective against the bird flu. Two other medications, oseltamivir and zanamivir, may still be effective against bird flu in its present form, according to the Centers for Disease Control and Prevention.

What's the risk to people in the United States?

So far Americans are at low risk from the bird flu outbreak, according to the CDC. The strain of virus causing the bird flu (highly pathogenic H5N1) hasn't been found in the United States. Migrating birds are being monitored for the H5N1 virus and public health workers are keeping a close watch on travelers from affected countries, however.

What can be done to control bird flu?

Bird flu has become so entrenched in Asia that it may never disappear. At this point, experts can only hope to contain it and, if possible, prevent a human epidemic. Asian countries are searching for outbreaks of bird flu in chickens and ducks and are destroying any affected flocks. But because many of the outbreaks occur on small family farms scattered throughout the countryside, not all outbreaks are reported or discovered by authorities, according to the World Health Organization.

In the United States, health officials have put together pandemic bird flu prevention measures. The Food and Drug Administration (FDA) has approved the first U.S. vaccine against bird flu. While there has only been one reported case of human bird flu in the United States, in 2003, the vaccine could provide limited early protection against widespread infection. Having a vaccine readily available in case there is an outbreak will buy time for health officials who could then develop a vaccine tailor-made to the specific strain of bird flu that develops in the United States.

The bird flu vaccine, derived from a human strain of the virus, immunizes adults 18- to 64-years-old and will be available to those who are at increased risk of exposure to bird flu. The vaccine will not be available commercially, but the federal government has already purchased it as part of the U.S. Strategic National Stockpile and will distribute it as needed.

Meanwhile, the CDC is training state laboratories in molecular techniques to identify H5N1 viruses, working with the World Health Organization to investigate the bird flu virus in Vietnam, doing lab testing of H5N1 viruses, and planning new vaccines.

What can I do to protect myself?

Since bird flu is limited to Asia, parts of Europe, the eastern Mediterranean, and Africa, there's no reason to take extra precautions in other places. At this point, the World Health Organization has not yet advised travelers to avoid any countries because of bird flu, and the risk of getting it is low.

But if you do travel to any of the more than 50 countries that has reported a bird flu outbreak in poultry or wild birds (including Thailand, Japan, Korea, India, Nigeria, Russia, and Zimbabwe), avoid poultry farms, contact with animals in live food markets, or surfaces that appear to be contaminated by feces from poultry or other animals. The CDC also advises travelers to clean their hands frequently with soap and water or an alcohol-based hand cleaner. In addition, travelers to affected countries should only eat poultry products -- such as chicken or eggs -- that have been thoroughly cooked. Heat destroys influenza virus.

References

Cumulative Number of Confirmed Human Cases of Avian Influenza A/(H5N1) Reported to WHO, World Health Organization/, March 2011.

Centers for Disease Control and Prevention. Avian Influenza (Flu): Current H5N1 Situation. Last updated, 2008.

CDC. Outbreak Notice, Update: Notice to Travelers about Avian Influenza A (H5N1). Updated July 14, 2006

CDC. Masks and Respirator Factsheet, updated May 8, 2007. What Your should Know About Using Masks and Respirators During a Flu Pandemic.

Associated Press. Bird flu called global human threat. http://www.washingtonpost.com/wp-dyn/articles/A46424-2005Feb23.html

World Health Organization. Advice to international travelers. February 2004. http://www.who.int/csr/disease/avian_influenza/travel_2004_02_11/en/

Stohr, K. and M. Esveld. Will vaccines be available for the next influenza pandemic? Science. December 24, 2004. 306: 2195-2196.Page: 5

Snacken, Rene et al. The Next Influenza Pandemic: Lessons from Hong Kong 1997. Emerging Infectious Diseases. Volume 5, No 2, March through April 1999 http://www.cdc.gov/ncidod/eid/vol5no2/snacken.htm#Table

Bird Flu: The Next Pandemic? Animesh Roul. Article No. 17, November 9, 2004. Efficient Feline to Feline Tranmission of Bird Flu. Recombinomics Commentary, March 12, 2005. http://www.recombinomics.com/news

Food and Drug Administration. FDA Approves First US Vaccine for Humans Against the Avian Influenza Virus H5N1. April 2007. http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/2007/ucm108892.htm

World Health Organization. H5N1 avian influenza: timeline of major events. July 2008. http://www.who.int/csr/disease/avian_influenza/Timeline_08%2007%2014%20_2_.pdf

Centers for Disease Control and Prevention. Questions and Answers about Avian Influenza and Avian Influenza A Virus. Last updated, 2008. http://www.cdc.gov/flu/avian/gen-info/qa.htm

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