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.
Avian influenza has been getting increasing worldwide attention from medical authorities. A new subtype of the virus called H5N1, which first infected chickens and then humans in Hong Kong in 1997, can cause disease with a high rate of mortality (death) in humans.
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 and Complications
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:
- aching muscles
- sore throat
- eye irritation
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.
Making the Diagnosis
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.
Treatment and Prevention
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, there is a vaccine that is reserved in stockpiles 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:
- destroying birds carrying or suspected of carrying the virus: When the virus is detected in birds, the priority is to quickly reduce the chance of spreading the disease to humans by detecting and destroying infected and exposed birds. The virus dies if heated at 56°C for 3 hours or 60°C for 30 minutes.
- disinfecting farm equipment, clothing, and boots: Boots, other farm equipment, and even rodents can act as vehicles that move the virus from farm to farm. Removing the virus from areas of infection requires the use of disinfectants like formalin and iodine compounds.
- limiting, restricting, or banning the shipment of live birds within and between countries that have had bird flu epidemics: Spread of the virus from farm to farm is possible due to the virus being excreted in bird droppings. Quarantine of farms is necessary to reduce the spread of the disease.
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:
- Get a flu shot. It won't prevent avian influenza, but it can prevent some strains of human influenza. This helps avoid the situation of becoming infected with both avian and human influenza at the same time. Having both infections increases the risk that the avian and human viruses will share genes, leading to potentially dangerous virus mutations.
- Avoid small farms where birds are grown in large numbers.
- Avoid raw eggs and foods made with eggs (e.g., mayonnaise, ice cream).
- Avoid open-air markets.
- Use alcohol-based hand sanitizer or wash your hands with soap and water frequently.