What is avian influenza?

Avian influenza, or bird flu, is an infection caused by avian (bird) influenza (flu) viruses. These flu viruses occur naturally among birds. Wild birds worldwide carry the viruses in their intestines, but usually do not get sick from them. However, bird flu is very contagious among birds and can make some domesticated birds, including chickens, ducks, and turkeys, very sick and kill them. Bird flu viruses do not usually infect humans, although there have been several cases of human infection with bird flu viruses since 1997.

Symptoms. Symptoms of bird flu in humans have ranged from typical flu-like symptoms (fever, cough, sore throat and muscle aches) to eye infections, pneumonia, severe respiratory diseases (such as acute respiratory distress), and other severe and life-threatening complications. The symptoms of bird flu may depend on which virus caused the infection.

Spreading the disease. Infected birds shed flu virus in their saliva, nasal secretions, and feces. Susceptible birds become infected when they have contact with contaminated excretions or surfaces that are contaminated with excretions. It is believed that most cases of bird flu infection in humans have resulted from contact with infected poultry or with contaminated surfaces.

Treatment. Studies suggest that the prescription medicines approved for human flu viruses would work in preventing bird flu infection in humans. However, flu viruses can become resistant to these drugs, so these medications may not always work.

Risk. The risk from bird flu is generally low for most people because the viruses occur mainly among birds and do not usually infect humans. However, during an outbreak of bird flu among poultry (domesticated chicken, ducks, turkeys), there is a possible risk to people who have contact with infected birds or surfaces that have been contaminated with excretions from infected birds. The current outbreak of avian influenza A among poultry in Asia is an example of a bird flu outbreak that has caused human infections and deaths. In such situations, people should avoid contact with infected birds, or contaminated surfaces, and should be careful when handling and cooking poultry.

Outbreaks. During late 2003 and early 2004, outbreaks of avian influenza occurred among poultry in eight countries in Asia (Cambodia, China, Indonesia, Japan, Laos, South Korea, Thailand, and Vietnam). At that time, more than 100 million birds, in the affected countries, either died from the disease or were killed in order to try to control the outbreak. By March 2004, the outbreak was reported to be under control. However, beginning in late June 2004, new deadly outbreaks of avian influenza among poultry were reported by several countries in Asia (Cambodia, China, Indonesia, Malaysia [first-time reports], Thailand, and Vietnam). It is believed that these outbreaks are ongoing.

Human infections of avian influenza have been reported in Thailand, Vietnam, and Cambodia. The death rate for these reported cases has been about 50 percent. Most of these cases occurred from contact with infected poultry or contaminated surfaces; however, it is thought that a few cases of human-to-human spreading of flu have occurred. If the virus was able to infect people and spread easily from person to person, a worldwide outbreak of disease called an influenza pandemic could begin.

Treatment. The virus is resistant to amantadine and rimantadine, two antiviral medications commonly used for influenza. Two other antiviral medications, oseltamavir and zanamavir, would probably work to treat flu caused by the virus, though studies still need to be done to prove that they work.

Vaccine availability. There currently is no vaccine to protect humans against the virus that is being seen in Asia. However, vaccine development efforts are under way. Research studies to test a vaccine to protect humans against the virus began in April 2005.

The current risk to Americans from the bird flu outbreak in Asia is low. There have been no human cases of bird flu in the United States. It is possible that travelers returning from affected countries in Asia could be infected. Since February 2004, medical and public health personnel have been watching closely to find any such cases.

CDC recommendations. The Center for Disease Control (CDC) currently advises travelers to countries in Asia, with known outbreaks of influenza A, to avoid poultry farms, contact with animals in live food markets, and any surfaces that appear to be contaminated with feces from poultry or other animals.