Avian influenza, more commonly called "bird flu," is a type of influenza or "flu" that occurs in all species of birds. The virus that causes avian influenza exists naturally in many wild birds, including wild waterfowl, without causing the condition in them (these birds are called carriers). The virus is usually associated with birds raised on poultry farms.
Most people may not immediately make the connection between avian influenza and humans. Avian influenza is rare in humans. When it does infect a human, the virus often causes serious illness or death.
Bird flu is caused by a virus. There are several different subtypes of the virus that have been known to cause the condition in people, including H7N9 and H5N1. The letters H and N in the subtype name stand for proteins found on the surface of the virus that are used to distinguish between different subtypes.
Pathogenicity is a measure of how likely a virus is to cause disease. In the case of the bird flu virus, it can have either low or high pathogenicity. Different subtypes of the virus cause either a mild form of the condition or an extremely contagious and highly dangerous form that spreads quickly.
Influenza viruses are constantly changing their genes. This process is called mutation.
These gene changes determine whether the virus will cause a mild condition or a deadly condition in the infected person or animal. The bird flu virus that affects birds has at least 15 different subtypes and usually only affects the bird population. The most dangerous subtype is the H5N1 subtype.
When the virus is found in humans, it is said to have "jumped the species barrier." This means that the virus has mutated in a way that allows it to cause the condition in humans. Because humans have no natural protection or immunity to the virus, they are likely to become ill very quickly and possibly die due to complications of the bird flu.
Bird to human transmission: Birds such as turkeys, geese, and domestic chickens come in contact with the virus from food, water, or particles contaminated with the virus. The virus can be shed in the droppings of migratory birds since they are natural carriers and is able to survive for 3 months in cool temperatures. It can also survive in water at 0°C for more than 30 days and at 22°C for up to 4 days. Transmission of the virus from birds to humans occurs when a person working closely with these animals inhales dust particles containing the virus or by other means.
In countries where live birds (e.g., chickens, geese, turkeys) are sold in markets along with pigs or raised near pigs, the possibility of the virus recombining with other subtypes is greater. This is because both human and avian viruses can infect pigs. If a pig is infected with both viruses at the same time, different parts of the avian and human viruses can mix with each other. Later, the avian virus that has picked up some genes from the human form of the influenza virus is able to more easily cause the condition in humans.
Human to human transmission: Although the vast majority of human cases of bird flu are the result of direct contact with an infected bird, rare cases of direct human-to-human spread have been reported.
Symptoms of the condition in birds depend on the pathogenicity of the virus that infects a bird. A virus that is not highly pathogenic causes mild illness. This form of the condition produces ruffled feathers or a decrease in egg production in infected birds. The highly pathogenic form of the virus can kill so quickly that once the virus enters the bird, the bird may die the same day.
In humans, bird flu causes symptoms similar to the typical flu. People may complain of any of the following:
The symptoms usually appear within 1 to 5 days after contact with the virus. The condition may be life-threatening because of the complications that can occur. These include viral pneumonia and extreme difficulty breathing.
A doctor can perform tests that identify the flu virus by swabbing the nose or throat. If you have recently travelled to an area of the world where avian flu occurs and have any of the symptoms of the flu, you should see your doctor.
Be sure to tell the doctor where you have visited and whether or not you were at a farm or open market with live animals.
There are treatments to help those with bird flu. Neuraminidase inhibitors (e.g., oseltamivir, zanamivir) is the class of medication that has been shown to be effective in reducing bird flu-related deaths.
There is no preventative vaccine for bird flu currently available to the public. However, H5N1 vaccines can be quickly procured by the government in case of a pandemic.
Preventing the spread of bird flu is a global effort. Steps taken to prevent the disease or stop the spread of disease include:
There are ways to protect yourself from catching the bird flu. People who are travelling in areas where the bird flu has occurred need to take special precautions to reduce the chance of exposure to the bird flu virus. Keep these tips in mind when travelling:
*All medications have both common (generic) and brand names. The brand name is what a specific manufacturer calls the product (e.g., Tyleno®). The common name is the medical name for the medication (e.g., acetaminophen). A medication may have many brand names, but only one common name. This article lists medications by their common names. For information on a given medication, check our Drug Information database. For more information on brand names, speak with your doctor or pharmacist.