Avian influenza ("bird flu")

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Outbreaks of highly pathogenic H5N1 avian influenza ("bird flu") began on poultry farms in Southeast Asia in December 2003. The outbreak was initially controlled by mass culling of millions of birds, but recurred in July 2004 and has spread steadily since then. Since July 2004, cases have been reported from poultry farms in Viet Nam, Thailand, China, Cambodia, Indonesia, Malaysia, Myanmar, Turkey, Russia, Albania, Czech Republic, Hungary, Poland, Romania, the Ukraine, France, Germany, Denmark, Israel, Jordan, Iraq, Iran, Kuwait, India, Bangladesh, Pakistan, Kazakhstan, Azerbaijan, Afghanistan, Egypt, Nigeria, Niger, Benin, Togo, Ghana, Sudan, Burkina Faso, Cote d'Ivoire, Djibouti, and Cameroon. Recently, cases have also been reported in migratory birds in the United Kingdom, Austria, Sweden, Switzerland, Greece, Italy, Poland, Hungary, Croatia, Bulgaria, Georgia, Czech Republic, Serbia and Montenegro, Bosnia and Herzegovina, Slovakia, Slovenia, Spain, Mongolia, and Hong Kong (significant because migratory birds are thought to be involved in spreading the disease from one country to another).

A total of 385 human cases have been identified to date: 137 from Indonesia, 106 from Viet Nam, 50 from Egypt, 30 from China, 25 from Thailand, 12 from Turkey, 8 from Pakistan, 8 from Azerbaijan, 7 from Cambodia, 3 from Iraq, 2 from Laos, and one each from Bangladesh, Nigeria and Djibouti. At the present time, most of the new cases are being reported from Indonesia, Viet Nam, Egypt, and China. More than half of the cases have been fatal. Most have occurred in those who had direct contact with live, infected poultry, or, in a much smaller number of cases, sustained, intimate contact with family members suffering from the disease. However, in one quarter or more of cases, the source of exposure is unclear. Unlike human influenza, the greatest mortality is seen in young people (those between the ages of 10 and 49).

The incubation period of avian influenza is usually 2-8 days, but may range up to 17 days. The illness usually begins with typical flu-like symptoms: high fevers, chills, body aches, dry cough. The infection may also begin with diarrhea, vomiting, or abdominal pains. Runny nose and sore throat are usually not part of the symptom complex. In severe cases, the infection progresses rapidly to pneumonia and respiratory failure, which are the most common causes of death.

The U.S. Food and Drug Administration recently approved a new test to diagnose H5N1 and other influenza infections in humans, called the Human Influenza Virus Real-Time RT-PCR Detection and Characterization Panel (see the FDA website).

There are no proven therapies for H5N1 infections. There are limited data that some of the newer antiviral agents, such as oseltamivir (Tamiflu) and zanamivir (Relenza) (PDF), may be active against H5N1 influenza viruses in the test tube. Tamiflu-resistant strains have been isolated from patients in Viet Nam and Egypt, but most strains remain susceptible (see the New England Journal of Medicine and the World Health Organization). When used for avian influenza, it may be appropriate to give Tamiflu in higher doses and for a longer period of time than when used for human influenza (consider a regimen of 150 mg twice daily for 10-14 days). Limited data suggest that Tamiflu is most effective when given early in the illness (see Roche Pharmaceuticals. A vaccine for avian influenza was recently approved by the U.S. Food and Drug Administration (FDA), but produces adequate antibody levels in fewer than half of recipients and is not commercially available. The vaccine is being stockpiled by the U.S. government in the event of a public health emergency. See the FDA website for further information. The vaccines for human influenza do not protect against avian influenza.

At present, the Centers for Disease Control and the World Health Organization do not recommend any travel restrictions for any country currently experiencing outbreaks of avian influenza. However, those traveling to these countries should avoid contact with live poultry, including visits to poultry farms and open markets with live birds, and should not touch any surfaces that may be contaminated with feces from poultry or other animals. Infected poultry are known to shed large amounts of virus in their droppings. The virus may survive for more than a month in bird droppings in cold weather and for nearly a week even in summer. Also, travelers should make sure all poultry and egg products are thoroughly cooked. Lastly, careful and frequent handwashing is strongly encouraged. Anyone who develops fever and flu-like symptoms after travel to a country with avian influenza should seek immediate medical attention.

The reason why public health authorities are alarmed about avian influenza is that, although these viruses pose little risk to the human population at present, they might develop the ability to infect humans in the future, perhaps by acquiring genes from human influenza viruses. Since humans do not have immunity to avian influenza viruses, this could lead to a massive worldwide pandemic. For an excellent summary of the world situation as of the end of 2006, go to Eurosurveillance. For further information on avian influenza, go to the World Health Organization, the OIE, the Centers for Disease Control, and the New England Journal of Medicine. Also see the special issue of Science (April 21, 2006). For a map showing the areas involved by the current outbreak, go to the European Union website.

There are a number of other strains of avian influenza (e.g. H7N2, H7N3, H7N7) that pose little risk to humans. Cases are almost entirely limited to those who have had direct contract with infected poultry or their droppings. Symptoms are typically mild: either conjunctitis ("pink-eye") or a flu-like illness. For a review of low pathogenicity avian influenza, go to Eurosurveillance.

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