Overview of Bird Flu (Avian Flu)

Bird flu, also called avian flu or avian influenza (AI), is an infectious disease caused by strains of influenza A viruses. Avian influenza is highly contagious in bird populations throughout the world. It often spreads through the migration of water birds. While many types of wild birds can carry the influenza virus without becoming ill, other types of birds (e.g., domestic birds such as chickens, turkeys, and ducks) develop disease when infected with avian flu viruses.

In domestic birds, one form of avian flu is common and usually mild, and one form is rare and more severe. The mild form of the disease is called LPAI (low pathogenic or "low path" avian influenza). Symptoms of this type include ruffled feathers and low egg production. The severe form is called HPAI (high pathogenic or "high path" avian influenza). In birds, HPAI develops suddenly, spreads quickly, and often causes death within 48 hours.

Influenza viruses rarely infect other species; for example, viruses that infect pigs usually do not infect horses. When people are infected with these viruses, they usually develop only mild symptoms (e.g., cough, fever, muscle aches, eye infections).

Incidence & Prevalence of Bird Flu

According to the World Health Organization (WHO), outbreaks of bird flu in poultry have occurred in the following countries:

  • Cambodia
  • China
  • Croatia
  • Indonesia
  • Japan
  • Kazakhstan
  • Lao People's Democratic Republic (Lao PDR)
  • Malaysia
  • Mongolia
  • Republic of Korea
  • Romania
  • Russian Federation
  • Thailand
  • Turkey
  • United States
  • Viet Nam

Since November 2003, H5N1 avian influenza infection in people has been reported in 12 countries, including the following:

  • Azerbaijan
  • Cambodia
  • China
  • Djibouti
  • Egypt
  • Indonesia
  • Iraq
  • Lao People's Democratic Republic (Lao PDR)
  • Nigeria
  • Thailand
  • Turkey
  • Viet Nam

In 2007, the highest number of cases of H5N1 infection in people occurred in Indonesia and Egypt. In most of these cases, human infection appears to have resulted from exposure to the saliva, nasal secretions, and feces of infected poultry or wild birds, for example, at a live poultry market.

In 2013, the World Health Organization (WHO) reported the first human influenza A (H7N9) infections in China. According to the WHO, a number of laboratory-confirmed human cases and deaths have occurred since 2013. The situation is being monitored closely. There is no evidence of ongoing human-to-human transmission of H7N9 so far, and no additional safety measures or precautions are necessary at this time.

U.S. Outbreak in Birds

According to the U.S. Centers for Disease Control and Prevention (CDC), the U.S. Department of Agriculture (USDA), and the U.S. Department of Interior (DOI), an outbreak of HPAI H5 was detected in poultry, captive wild birds, and wild birds in the United States beginning in December 2014.

As of August 2015, more than 48 million chickens and turkeys had died or had been slaughtered to reduce the risks associated with the virus. No human cases had been reported. The CDC reports that the risk for transmission to humans appears to be low—indicated by a lack of genetic markers used in the past to identify the risk for human infection.

The outbreak was first detected on the West coast, moved east affecting several states, and hit the Midwest (e.g., Iowa, Wisconsin, Minnesota) hard. Several countries banned U.S. poultry imports and egg prices rose sharply in response to this outbreak. The CDC and other agencies warn that cooler temperatures and wild bird migrations in the fall of 2015 could spread the virus further.

Updated by Remedy Health Media

Publication Review By: Stanley J. Swierzewski, III, M.D.

Published: 01 Aug 2007

Last Modified: 12 Aug 2015