Background
While initially making its appearance in the United States in poultry farms along the eastern seaboard in Delaware and Pennsylvania, bird flu, avian influenza virus, is not limited to birds. This influenza virus can infect several animal species including birds, pigs, horses, seals and whales. Influenza viruses that infect birds are called “bird flu.” Public health authorities, including the CDC, monitor outbreaks closely because of concerns about the potential for more widespread infection in the human population.

Birds are a critical component in the spread of avian influenza because all known subtypes of influenza A viruses circulate among wild or migratory birds. Avian influenza usually does not make the natural hosts, wild birds, ill, but can make domesticated birds very ill and kill them. Avian influenza A viruses do not usually infect humans, although several instances of human infections and outbreaks have been reported since 1997.

Two notable outbreaks in Hong Kong, in 1997 and 1999 resulted in fewer than 20 human cases, but among them six deaths and caused authorities to destroy over a million chickens to stop the spread of the virus evidenced in bird to human transmission. By 2003 there was evidence, in small outbreaks in China and the Netherlands, that human-to-human transmission was occurring.

The current outbreak appears to be the most widespread in recent times. According to the World Health Organization (WHO), infection with the virus and several deaths among humans and for the first time, domestic cats, were confirmed by laboratory tests in Thailand. Vietnam has confirmed the virus in humans. Outbreaks among poultry have already been confirmed in Cambodia, Hong Kong, Indonesia, Laos and South Korea. Human to human transmission there has not been established. Japan has been confirmed as the site of two outbreaks and China has confirmed 53 outbreaks and is in the process of depopulating (WHO term) millions of chickens, ducks and geese.

In the United States, Delaware officials confirmed in early February that a flock of non-commercial chickens had tested positive for avian influenza virus. The strain of the virus detected was a different form of the avian influenza virus currently affecting poultry and humans in Asia. All birds from the affected flocks were destroyed, though health officials indicated that there was never a health risk to humans.

What sets "bird flu" – avian influenza, apart from other flu?

The Technical Explanation*
During winter it is fairly typical to see folks getting the flu — flu that is caused by viruses of the same family. According to a briefing paper from the FDA's Center for Veterinary Medicine, particular “varieties” of flu are identified by subtypes based on the presence of proteins on the surface of the virus.

These proteins, called hemagglutinin and neuraminidase, are abbreviated simply as H and N. There are currently 15 known H subtypes and 9 known N subtypes, and so they can occur in any combination; 9 times 15, potentially 135 different combinations of the H and N subtypes. Humans get only three types: H1, H2, and H3.

Type A flu is illusive, and it has the ability to shift its genes around. That happens when it picks up a new H gene from an animal flu virus. H5 and H7 viruses can become highly pathogenic (determined either by the genetic sequencing on the virus, or the ability to cause disease and death in other birds) even if they start out as a low pathogenic form. Thus, when an H5 or an H7 virus is found they are classified through further testing as either as either highly pathogenic or low pathogenic.

Looking at the outbreaks in the United States this year and using the method of identifying the viruses described by the FDA (H and N subtypes), the two flocks in Delaware are a low pathogenic version of H7N2. The virus that currently is affecting Asia is a highly pathogenic H5N1. A flock in Pennsylvania was identified as H2N2 and is being treated as a low path. The last record of a highly pathogenic avian influenza virus in the United States was in1983-84. Affecting commercial poultry in both Pennsylvania and Virginia, it was a high path H5N2.

[ *Information summarized from a Technical Briefing on Animal Health Issues by Dr. Ron DeHaven, Chief Veterinary Officer, Texas Animal Health commission, Dr. Nancy Cox, Centers for Disease Control and Dr. Steve Sundlof, FDA's Center for Veterinary Medicine Washington D.C., February 23, 2004]

What are the risks?
Avian influenza is a very highly contagious disease. Exposure of poultry to migratory waterfowl seems to be the most likely cause or certainly the ongoing reservoir of infection. But once established, moving poultry, poultry equipment and people from one infected premise to another pose the risk of introducing avian influenza into other premises and certainly into commercial poultry.

Once in a flock, the spread of the disease can occur from bird to bird, by direct contact and then typically from farm to farm through people, equipment and other mechanical means of transmitting the virus. The FDA and CDC do recommend that farms and poultry producers take extra precaution by disinfecting any equipment or items that come into contact with poultry and that waste is disposed of properly.

Consumers who wish to avoid or minimize risk are advised to cleanse their hands often using soap and water when handling and preparing poultry and be certain to thoroughly cook all foods from poultry, including eggs. (The virus IS sensitive to heat and can be destroyed by cooking.)

What are the symptoms of avian influenza virus in people?
People who have contracted avian influenza virus from poultry begin experiencing typical flu-like symptoms. 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, pneumonia, acute respiratory distress, viral pneumonia, and other severe and life-threatening complications.

Though no human cases of the virus have been confirmed in the United States or any of North America, as a precaution the CDC recommends that people who have traveled to East Asia see a health care processional immediately if they develop flu-like symptoms. Be certain to provide information about having visited areas of virus outbreak so that proper tests can be performed.

Treatment for avian influenza
Studies to date suggest that the prescription medications approved for human influenza strains may be effective in preventing avian influenza infection in humans. However, because flu strains mutate and can become resistant to these drugs, the medication may not be effective in all cases.
Thus far in this outbreak, human cases have been blamed on direct contact with infected chickens and their droppings. People who catch the virus from birds can pass it on to other humans, although the disease is generally milder in those who caught it from an infected person rather than from birds. If the virus mutates and combines with a human influenza virus, it could be spread through person-to-person transmission in the same way the ordinary human flu virus is spread.

There is no vaccine available at this point, though development is underway.
The U.S. Center for Disease Control and Prevention offers complete information on avian influenza in French, Spanish, Traditional Chinese, Vietnamese, Japanese, Thai and Korean in a special section of their Web site. See www.cdc.gov/flu/languages.htm.