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Bird Flu (H5N1, H7N9)

Bird Flu Overview

Bird flu (also termed avian influenza) is an illness that affects wild and domesticated birds that usually causes either little or no symptoms unless the bird population is susceptible, in which it may cause death in birds within about 48 hours. This influenza A virus primarily affects birds and is not easily able to infect people. However, in the late 1990s, a new strain of bird flu arose that was remarkable for its ability to cause severe disease and death in domesticated birds such as ducks, chickens, or turkeys. As a result, this strain was called "highly pathogenic" (meaning very severe) avian influenza (HPAI, a term seen in older publications). The first human case of illness from highly pathogenic avian influenza was identified in 1997, and about 622 infected people have been identified by March 2013, mainly infected by strain H5N1. Human infection with bird flu is rare but frequently fatal. More than half of those people infected (over 370 infected people) have died (a current estimate of the mortality rates in humans is about 60%).

The Chinese government announced they detected a new strain of bird flu in March 2013. It is named H7N9 (also termed H7N9 Chinese bird flu). As of Apr. 7, 2013, about 21 people in China have been infected and six have died (others are very ill). Most people infected had contact with infected birds (chickens), and currently there is no good evidence that H7N9 is transmitted from person to person although this situation is being closely watched for any changes. Although the H7N9 has been detected only in China (Shanghai and several other smaller cities). The patients usually come from areas where they have a likelihood of direct contact with infected birds. Other big cities in China (Beijing, Hong Kong) have not reported infections to date. In April 2013, the WHO (World Health Organization) started publishing daily updates on the H7N9 infections and deaths reported in China.

First, here are some definitions to put the bird flu threat into perspective:

  • Pandemic: A pandemic is a global outbreak of disease. This could occur if a new virus (mutated from a bird flu virus) that causes serious illness were to emerge among humans (not birds) with the ability to spread easily from one person to another. A pandemic is caused by a new subtype that has never (or not recently) occurred in humans. The last pandemic involving humans was with an influenza virus, H1N1 (often termed the "swine flu"), that occurred in 2009.
  • Epidemic: A fast-spreading, seasonal, or regional outbreak of flu among humans is called an epidemic. Epidemics may lead to pandemics; there have been several bird flu epidemics in avian and domestic birds (for example, chickens and turkeys) in several regions of the world (see below).

Birds have been affected with avian influenza in Asia, Europe, the Near East, and Africa, and the outbreak has killed millions of poultry. Bird flu from the highly pathogenic strain is not currently found in the United States. Human cases of bird flu have largely been confined to Southeast Asia and Africa. However, mutations (changes in the genetic material of the virus) often occur in the virus, and it is possible that some mutations could create a more contagious virus that could cause a worldwide pandemic of flu among humans. Fortunately, the mutations that have occurred to date in nature have not made the virus more contagious. Unfortunately, recent research work has been able to introduce genetic material into bird flu viruses that makes these laboratory strains highly transmissible to humans. This will be discussed in another section.

The virus spreads from bird to bird as infected birds shed flu virus in their saliva, nasal secretions, and droppings. Healthy birds get infected when they come into contact with contaminated secretions or feces from infected birds. Contact with contaminated surfaces such as cages might also allow the virus to transfer from bird to bird. Contact with humans occurs in the same way, mainly by flocks of chickens cultivated by farmers that are exposed to wild birds infected with bird flu. Other people are exposed to the bird flu when, for example, infected birds are processed for sale before they are cooked or if they come in contact with contaminated wild bird droppings or dead birds.

Medically Reviewed by a Doctor on 4/9/2013
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