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AVIAN INFLUENZA
(Bird Flu)

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OVERVIEW

H5N1 outbreaks in 2005 and Poultry density. Click to enlarge image.
Avian influenza, a form of Influenza A virus is an infection caused by avian (bird) influenza (flu) viruses. These influenza viruses occur naturally among birds. Wild birds worldwide carry the viruses in their intestines, but usually do not get sick from them.

Avian Flu was first recorded in Italy more than 100 years ago in 1878. As the cause of massive poultry epidemics, this disease was then known as "Fowl Plague". This disease reared its ugly head in the United States in 1924-25, and then again in 1929. In 1955, it was determined that the virus causing Fowl Plague was one of the influenza viruses. All influenza viruses affecting domestic animals (equine, swine, avian) belong to Type A, and Type A influenza virus is the most common type producing serious epidemics in humans. Types B and C do not affect domestic animals.

Humans can be infected with influenza types A, B, and C viruses. Subtypes of influenza A that are currently circulating among people worldwide include H1N1, H1N2, and H3N2 viruses.B 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.

Outbreaks of avian influenza H5N1 have occurred among poultry in eight countries in Asia (Cambodia, China, Indonesia, Japan, Laos, South Korea, Thailand, and Vietnam) during late 2003 and early 2004. 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 outbreaks. By March 2004, the outbreak was reported to be under control. Since late June 2004, however, new outbreaks of influenza H5N1 among poultry were reported by several countries in Asia (Cambodia, China [Tibet], Indonesia, Kazakhstan, Malaysia, Mongolia, Russia [Siberia], Thailand, and Vietnam). It is believed that these outbreaks are ongoing. Influenza H5N1 infection also has been reported among poultry in Turkey Romania, and Ukraine. Outbreaks of influenza H5N1 have been reported among wild migratory birds in China, Croatia, Mongolia, and Romania.B (see map)

As of January 7, 2006, over 140 human cases of Avian influenza A (H5N1) infection have been reported in Cambodia, China, Indonesia, Thailand, Vietnam, and most recently, several cases in Turkey. A January 9, 2006 WHO Situation Report describes detection of the H5 subtype of avian influenza virus in samples from an additional 10 people in Turkey . These samples are undergoing further analysis to determine whether they contain the H5N1 strain.

EPIDEMIOLOGY


Reservoir:

Infected birds

Mode of Transmission:

Avian influenza is very contagious among birds and can make some domesticated birds, including chickens, ducks, and turkeys, very sick and kill them. Infected birds shed influenza virus in their saliva, nasal secretions, and feces. Susceptible birds become infected when they have contact with contaminated secretions or excretions or with surfaces that are contaminated with secretions or excretions from infected birds.

So far, the spread of H5N1 virus from person to person has been limited and has not continued beyond one person. Nonetheless, because all influenza viruses have the ability to change, scientists are concerned that H5N1 virus one day will mutate and be able to infect humans and spread easily from one person to another. Because these viruses do not commonly infect humans, there is little or no immune protection against them in the human population. If H5N1 virus were to gain the capacity to spread easily from person to person, an influenza pandemic (worldwide outbreak of disease) could begin.

Incubation Period:

Most cases have occurred in previously healthy children and young adults. However, it is possible that the only cases currently being reported are those in the most severely ill people and that the full range of illness caused by the H5N1 virus has not yet been defined.

Unlike seasonal influenza, in which infection usually causes only mild respiratory symptoms in most people, H5N1 infection may follow an unusually aggressive clinical course, with rapid deterioration (1-3 days), and high fatality. Primary viral pneumonia and multi-organ failure have been common among people who have become ill with H5N1 influenza.

Methods of Control:


  1. Educate workers about the importance of strict adherence to and proper use of hand hygiene after contact with infected or exposed poultry, contact with contaminated surfaces, or after removing gloves. Hand hygiene should consist of washing with soap and water for 15-20 seconds or the use of other standard hand-disinfection procedures as specified by state government, industry, or USDA outbreak-response guidelines.

  2. Ensure that personnel have access to appropriate personal protective equipment (PPE), instructions and training in PPE use, and respirator fit-testing.

  3. Disinfect surfaces that may have become contaminated with secretions.



Treatment

Four different influenza antiviral drugs (amantadine, rimantadine, oseltamivir, and zanamivir) are approved by the U.S. Food and Drug Administration (FDA) for the treatment of influenza; three are approved for prophylaxis. All four have activity against influenza A viruses. However, sometimes influenza strains can become resistant to these drugs, and therefore the drugs may not always be effective. The H5N1 virus that has caused human illness and death in Asia 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 influenza caused by H5N1 virus, but additional studies still need to be done to demonstrate their effectiveness.

Additional References

www.fao.org/ag/againfo/subjects/en/health/diseases-cards/avian_bg.html

www.cdc.gov/flu/avian/gen-info/flu-viruses.htm#virusoverview

www.cdc.gov/flu/avian/gen-info/facts.htm

www.cdc.gov/flu/avian/gen-info/avian-flu-humans.htm

www.cdc.gov/flu/avian/outbreaks/asia.htm#assess

www.cdc.gov/flu/avian/professional/protect-guid.htm

www.cdc.gov/flu/avian/gen-info/qa.htm

www.nyas.org/ebriefreps/splash.asp?intebriefID=329

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