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Avian influenza or AI is a virus that primarily affects poultry. The disease can cause varying amounts of illness, and even death, among poultry that become infected. The virus can infect chickens, turkeys, pheasants, quail, ducks, geese, and guinea fowl, as well as a wide variety of other birds. Migratory waterfowl have proved to be the natural reservoir for this disease.
Fortunately, humans rarely become infected and when they do, it is typically through direct contact with the live bird - not the poultry consumers purchase in grocery stores.

Only one human infection has been documented in the United States in a poultry worker in Virginia. The reported symptoms of avian influenza in humans have ranged from typical influenza-like symptoms (e.g., fever, cough, sore throat, and muscle aches) to eye infections (conjunctivitis), pneumonia, acute respiratory distress, viral pneumonia, and other severe and life-threatening complications.

Potential Threat to Human Health

AI viruses can be classified into low pathogenic (LPAI) and highly pathogenic (HPAI) forms based on the severity of the illness they cause. Most AI virus strains are "low path" and typically cause little or no clinical signs in infected birds. However, some low-path virus strains are capable of mutating under field conditions into high-path trains which are much more serious and can destroy entire flocks.

Human Health Impact

Humans rarely become infected with avian influenza, though animal to human transmission has occurred. Person to person transmission has not been documented.

In some instances, strains of HPAI viruses can be infectious to people. Human infections with the avian influenza viruses under natural conditions have been documented in recent years. The H5N1 strain, isolated in Hong Kong in 1997, was highly pathogenic for chickens and caused a limited outbreak in 18 people. Six of these individuals died. Since mid-December 2003, a growing number of Asian countries have reported outbreaks of HPAI in chickens and ducks. The rapid spread of HPAI, with outbreaks occurring at the same time, is historically unprecedented and of growing concern for human health as well as for animal health.

According to the World Health Organization (WHO), particularly alarming is the HPAI strain of most of these outbreaks-H5N1-which has jumped the species barrier causing severe disease, with high mortality in humans. For this reason, poultry personnel and avian health care specialists should take precautionary measures, including wearing protective gear and following sanitary procedures, to reduce the risk of infection.
Of greater concern to WHO is the possibility that the present situation, if the virus acquires human influenza genes, can give rise to human-to-human transmission and possibly another influenza pandemic in people.

LPAI is spread primarily through direct contact between healthy birds and infected birds, and through indirect contact with contaminated equipment and materials. The virus is excreted through infected birds' feces and secretions from the nose, mouth, and eyes.

Cleaning and Disinfection

To prevent a possible outbreak of low pathogenic avian influenza, poultry producers must use special preventative measures and precautions on the farm. If low pathogenic avian influenza is detected, farms must be thoroughly cleaned and disinfected. Low pathogenic avian influenza is inactivated by heat and drying. It is also very sensitive to most disinfectants and detergents. In order to ensure that the cleaning and disinfecting process is thorough, however, the area to be disinfected must be clear of organic material.


HPAI is an extremely infectious and fatal form of the disease for chickens. The U.S. Department of Agriculture's (USDA) Animal and Plant Health Inspection Service (APHIS) works to keep HPAI from becoming established in the U.S. poultry population. HPAI can strike poultry quickly without any infection warning signs. Once established, the disease can spread rapidly from flock to flock. It is essential for the U.S. poultry industry to be alert to this disease threat. To prevent HPAI from being introduced into the United States, USDA requires that all imported birds (poultry, pet birds, birds exhibited at zoos, and ratites) be quarantined and tested for this virus before entering the country.

In addition to international import restrictions, APHIS and State veterinarians specially trained to diagnose foreign animal diseases regularly conduct field investigations of suspicious disease conditions. University personnel, State animal health officials, USDA-accredited veterinarians, and members of industry who report suspicious cases, assist this surveillance.

Furthermore, APHIS and State animal health officials work cooperatively with the poultry industry to conduct surveillance at breeding flocks, slaughter plants, live-bird markets, livestock auctions, and poultry dealers.

If HPAI were detected in U.S. poultry, APHIS veterinarians would work quickly with their State counterparts and the industry to implement measures such as quarantine, control, and cleanup to prevent opportunities for the virus to spread.

Introduction and Spread of HPAI Virus

Exposure of poultry to migratory waterfowl and the international movement of poultry, poultry equipment, and people pose risks for introducing HPAI into U.S. poultry. Once introduced, the disease can be spread from bird to bird by direct contact. HPAI viruses can also be spread by manure, equipment, vehicles, egg flats, crates, and people whose clothing or shoes have come in contact with the virus. HPAI viruses can remain viable at moderate temperatures for long periods in the environment and can survive indefinitely in frozen material. One gram of contaminated manure can contain enough virus to infect 1 million birds.

For more information on avian influenza, contact APHIS or visit the APHIS Web site at


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