Avian influenza/bird flu

Influenza (the flu) is a contagious respiratory illness caused by the influenza virus. Avian influenza, or bird flu, is caused by influenza viruses that normally affect birds. Since 1997, there have been several outbreaks of avian influenza in people. Any human outbreaks are closely monitored due to the potential spread of the disease.


Causes and associated factors
In people, the flu is caused by type A or type B influenza viruses. There are many subtypes of the type A virus, classified according to variations in two proteins found on the surface of the virus: hemagglutinin (HA) and neuraminidase (NA). The protein hemagglutinin has 15 possible variations. The protein neuraminidase has seven. A common subtype of the type A influenza virus that infects people is A(H3N2), which means that the type A influenza virus has a hemagglutinin 3 and neuraminidase 2 protein on its surface.
Various subtypes of type A influenza viruses can affect birds and a few other animals, such as pigs, horses, seals and whales. Those that primarily infect birds are known as avian influenza viruses. They've been known to exist for more than 100 years and are found worldwide. People were not thought to be affected by these viruses until 1997, when the avian influenza virus A(H5N1) was identified as the cause of illness in a number of people in Hong Kong. Since then, other avian influenza subtypes have also been identified in people, including A(H9N2), A(H7N2), A(H7N3) and A(H7N7). The A(H5N1) subtype is responsible for the 2003-04 outbreak of avian influenza in Asia, which caused illness and death in a number of people. Because people usually aren't infected with avian influenza viruses, their immune systems haven't developed natural defenses against them.

Viruses have the ability to mutate or change their genetic make-up. Over the course of a few months, some avian influenza viruses that cause mild illness have mutated to cause more severe illness. It's also thought that if a person is infected with a human flu virus and an avian flu virus at the same time, the avian virus may mutate by acquiring genes from the human virus. Such a mutation isn't known to have occurred at this time. If it does, it could potentially produce an avian virus that could spread easily from person to person, and one for which people have little or no immunity. The potential for mutation has made the control of avian flu outbreaks a priority for health officials.


Transmission
Avian influenza viruses are very contagious among birds. Wild birds, especially migratory waterfowl (such as ducks) are the natural hosts of avian influenza viruses. Wild birds often are resistant and don't become ill when infected with the virus. However, domestic birds (such as chickens and turkeys) may be more susceptible to illness, depending on the subtype of the virus. Domestic birds infected with the avian virus may become seriously ill and die quickly.
The avian virus is found in the saliva, nasal secretions and feces of infected birds. The illness spreads to other birds through contact with these contaminated excretions.

Most cases of avian influenza in people have occurred due to direct bird-to-human transmission of the virus. People are thought to become ill after being exposed to sick chickens or surfaces contaminated with infected bird secretions. Rarely, human-to-human transmission may have occurred. The average incubation period (time from exposure to the virus to appearance of symptoms) ranges from two to four days.


Avian flu in the United States
Even though strains of the avian influenza virus have been found in bird flocks in the United States for more than 20 years, there's only been one case of bird flu in humans in this country. That case occurred in New York in 2003, and the person fully recovered. The A(H7N2) avian virus was the strain involved. But, it's not known how the person became infected. In February and March 2004, the same strain of virus was discovered in chickens in Delaware and Maryland. This particular virus is common in birds throughout the world and is usually responsible only for mild illness in birds.

Signs and symptoms
The symptoms of bird flu in people may vary, often including:
typical flu symptoms such as fever, cough, sore throat and muscle aches
diarrhea or loose stools
eye infections
difficulty breathing
Some human infections have led to pneumonia, severe breathing difficulty or even death.


Diagnosis
Avian influenza is diagnosed based on your recent travel history, occupation, possible contact with infected birds, medical history and a physical exam. If your doctor suspects that you have avian flu, the Centers for Disease Control & Prevention (CDC) suggest that testing be considered in consultation with both state and local health departments. Secretions from the nose and throat and a blood sample may be tested in a lab. Chest X-rays and other tests may be done as well. Lab tests can help confirm the specific flu virus.

Treatment
Antiviral medications may be effective in treating avian influenza viruses. However, some viral subtypes appear to be resistant to certain antiviral medications. Other treatment measures, such as taking fever-reducing medications, may be recommended to control specific symptoms.

Complications
Complications of bird flu may include pneumonia, severe difficulty breathing or even death.

Pregnancy-specific information
Pregnancy doesn't appear to increase the risk of developing avian influenza. Currently, specific information about the effect of the illness on pregnancy is unavailable.

Senior-specific information
Currently, specific information about the effect of the illness on older adults is unavailable.

Prevention
In response to the 2003-04 avian flu outbreaks, the CDC and the U.S. Department of Agriculture (USDA) instituted measures to prevent the importation of birds from countries known to have the A(H5N1) strain of bird flu. Poultry farms found to have any avian flu strain are quarantined, and surveillance testing is conducted around these farms. Infected birds are destroyed and disposed of safely. The CDC recommends increased surveillance efforts by state and local health departments, hospitals and doctors to assure early identification of anyone suspected of having bird flu.
Currently, there isn't a vaccine available to the general public to protect people from avian flu. However, early testing of an avian flu vaccine showed promising results in providing protection to healthy adults. Testing on older people and children will be conducted soon.

The CDC hasn't recommended travel restrictions to countries with outbreaks of avian influenza. However, when traveling to areas where bird flu has been detected, you should avoiding areas with live poultry, including live animal markets and poultry farms, and avoiding contact with sick or dead poultry when visiting any of these countries. Wash your hands frequently with soap and water or a waterless alcohol-based hand sanitizer. If you're eating poultry or eggs, be sure they're thoroughly cooked. When you return home, monitor your health carefully for 10 days. If you develop any illness with fever or respiratory symptoms, consult your doctor. Be sure to let him or her know about your travel history and symptoms ahead of time. For the latest travel recommendations, call or check the CDC's Travelers' Health Web page at www.cdc.gov/travel.