Bird Flu (Avian Influenza, Avian Flu)
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Bird Flu Symptoms
Read about the outbreak of bird flu in Hong Kong
Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: Dennis Lee, MD
Bird flu (also referred to as avian flu), as the name implies, is an infection in birds caused by an influenza virus. Influenza viruses that infect birds often do not cause illness in birds. Since the viruses are highly contagious, danger to humans arises when domesticated birds (for example chickens, ducks, and turkeys) become infected. While bird flu usually poses no threat to humans, instances of transmission of bird flu to humans have been reported since 1997, and over 100 people were infected in an outbreak that began in Southeast Asia in mid-2003. In November 2010, officials in Hong Kong announced that a woman had contracted bird flu, the first reported case of the condition in seven years. The 59-year-old woman had recently traveled to mainland China but reported no contact with live poultry or visits to farms.
Bird flu facts
- Bird flu refers to strains of influenza that primarily affect wild and domesticated birds.
- Bird flu is also known as avian flu or avian influenza.
- Although bird flu is contagious and spreads easily among birds, it is uncommon for it to be transmitted to humans.
- In the late 1990s, a new strain of bird flu arose which was unusually severe ("highly pathogenic"), resulting in the deaths of hundreds of millions of birds, including poultry.
- Control efforts, including culling infected flocks and vaccinating healthy birds, have limited the spread of highly pathogenic bird flu.
- In 2011, a mutated strain of highly pathogenic bird flu appeared, which is concerning because the existing poultry vaccines are not very effective against the new strain.
- Human infection with the highly pathogenic strain of bird flu is uncommon, with fewer than 600 cases reported since 1997.
- Human infection occurs primarily in people who have close contact with sick poultry in countries where the virus is found. There have been isolated cases of human-to-human transmission.
- Human infection with bird flu is fatal in approximately 60% of cases.
- Bird flu from the highly pathogenic strain is not found in the United States at this time.
What is bird flu?
Bird flu (avian influenza) is a disease caused by an influenza virus that primarily affects birds. In the late 1990s, a new strain of bird flu arose that was remarkable for its ability to cause severe disease and death, especially in domesticated birds such as ducks, chickens, or turkeys. As a result, this strain was called highly pathogenic (meaning very severe) avian influenza.
Since the identification of highly pathogenic influenza, infected birds have been found in Asia, Europe, the Middle East, and Africa. Careful control measures, including destroying infected flocks and vaccinating healthy birds, have reduced the number of cases, but the virus continues to exist in poultry flocks in areas of Asia and Africa. Bird flu from the highly pathogenic strain is not found in the United States at this time.
The virus spreads from bird to bird through infected birds shedding the 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. Symptoms in birds range from mild drops in egg production to failure of multiple major organs and death.
The first human case of illness from highly pathogenic avian influenza was identified in 1997, and more than 560 cases have been identified since then, with deaths worldwide exceeding 300. Human cases of highly pathogenic bird flu have been largely confined to Southeast Asia and Africa. However, mutations often occur in the virus, and it is possible that some mutations could create a more contagious virus that could cause a regional epidemic or a worldwide pandemic of bird flu among humans. Fortunately, the mutations that have occurred to date have not made the virus more contagious, although the concern remains.
What causes bird flu?
Bird flu is caused by strains of the influenza virus that have evolved to be specially adapted to enter avian cells. There are three main types of influenza: A, B, and C. The virus that causes bird flu is an influenza A type with eight RNA strands that make up its genome. Influenza viruses are further classified by analyzing two proteins on the surface of the virus. The proteins are called hemagglutinin (H) and neuraminidase (N). There are many different types of hemagglutinin and neuraminidase proteins. The current highly pathogenic bird flu virus has type 5 hemagglutinin and type 1 neuraminidase. Thus, it is a "H5N1" influenza A virus.
There are many types of influenza viruses, and most prefer to live in a limited number of animals. Thus, swine flu primarily infects swine and bird flu primarily infects birds. Human influenza is best adapted to humans. A few cases may occur in an accidental host, such as when people who have extensive contact with sick birds get the bird flu. In addition to humans and birds, we know that pigs, tigers, leopards, ferrets, and domestic cats can sometimes be infected with avian influenza viruses.
Influenza viruses mutate easily and often. These mutations can arise spontaneously in a single virus or can occur when two different influenza strains get close enough together to exchange genetic material. There are two major types of mutations in influenza viruses: antigenic shifts, where large RNA segments are interchanged between different influenza virus type, and antigenic shifts, where small RNA sequences are changed. The antigenic shifts are usually responsible for developing new strains. For example, the 2009 swine flu pandemic was caused by a virus that included genetic material from pig influenza, avian influenza, and human influenza strains. New mutations can allow the virus to evade the body's immune system and makes older vaccines ineffective. In 2011, one strain of the highly pathogenic avian influenza virus mutated in this way, making the existing vaccine used against avian flu ineffective against the new strain. Sometimes a flu virus will mutate in a way that makes it able to infect a new species.
Serious pandemic influenza occurs when a relatively new strain of the influenza virus arises that is highly contagious to humans. The most deadly pandemic in modern history was the 1918 influenza, also known as the Spanish flu (although it did not originate in Spain). The 1918 virus spread rapidly and killed tens of millions of people worldwide. Mortality was especially high in healthy young adults. Although the 1918 virus was a human influenza virus it, had many genes that likely came from a strain of bird flu. One reason that health officials carefully watch for and try to limit human contact with birds that develop avian flu is to avoid chances for a new strain to arise that may prefer to develop in human tissue.
What are risk factors for bird flu?
Humans may get bird flu from contact with infected birds (chickens, for example) or their droppings or surfaces with infected droppings. Risk factors include caring for sick birds, killing sick birds, and preparing sick birds for consumption. Despite the large number of people who have contact with poultry every day in the world, human cases of bird flu remain rare. This highlights how difficult it is for the bird flu virus to infect human cells, but mutations like antigenic shifts may reduce such difficulties.
Although direct contact with sick poultry poses the highest risk, indirect exposure to bird feces is also a risk. Thus, contact with unwashed eggs from sick birds or water contaminated by poultry feces poses a potential risk of disease.
Human to human spread has occurred in isolated cases. Thus, caring for a person infected with bird flu is also a risk factor for the disease. There is a theoretical risk in laboratory workers who handle the avian flu virus. One alleged incident in 2009 occurred when a company inadvertently sent live avian flu virus samples to research laboratories, which subsequently were used to vaccinate ferrets. The contaminated vaccine did not result in any human cases of infection.
What are bird flu symptoms and signs?
Symptoms occur approximately two to eight days after exposure, on average. Infected people experience typical flu-like symptoms, including fever, cough, sore throat, and muscle aches. Some people also have nausea, vomiting, diarrhea, or eye infections. This can progress to pneumonia and even respiratory failure. Bird flu causes a very aggressive form of pneumonia (acute respiratory distress syndrome or ARDS) that is often fatal.
How is bird flu diagnosed?
Routine tests for human influenza A will be positive in patients with bird flu but are not specific for the avian virus. To make a specific diagnosis of bird flu, specialized tests are needed. In the United States, local health departments and the Centers for Disease Control and Prevention can provide access to the specialized testing. The virus can be detected in sputum by several methods, including culture or polymerase chain reaction (PCR). Culture should be done in laboratories that have an appropriate biosafety certification. PCR detects nucleic acid from the influenza A virus. Specialized PCR testing is available in reference laboratories to identify avian strains.
During and after infection with bird flu, the body makes antibodies against the virus. Blood tests can detect these antibodies, but this requires one sample at the onset of disease and another sample several weeks later. Thus, results are not available until the patient has recovered or died.
What is the treatment for bird flu?
Because of the small number of human cases, it has not been possible to conduct rigorous treatment trials for bird flu. The current recommendation from the World Health Organization is to use an antiviral medication called oseltamivir (Tamiflu). In Sept. 2011, the CDC stated the following: "Two other antiviral medications, oseltamivir and zanamivir, would probably work to treat influenza caused by H5N1 virus, but additional studies still need to be done to demonstrate their effectiveness."
What is the prognosis of bird flu?
The prognosis in human cases of bird flu remains poor. Many cases occur in people who are poor, live in rural areas in underdeveloped countries, and do not have access to modern intensive care units or antiviral therapy. Approximately 60% of people diagnosed with bird flu eventually die from the disease.
Can bird flu be prevented?
Bird flu can be prevented by avoiding contact with sick poultry originating in countries known to be affected by the virus. In 2011, Egypt has the most reported cases to date. Prevention also includes poultry safety measures such as destroying flocks when sick birds are identified and vaccinating healthy flocks. Combined with import bans, this culling has effectively limited the spread of bird flu in outbreak situations but naturally has negative effects on the poultry and egg industry. Unlike SARS which some investigators suggest has been eliminated from the world or Ebola which has a narrow geographic range, the bird flu continues to exist in significant areas of the world and can be spread widely by migrating birds.
Properly handling and cooking of poultry and eggs can kill viruses like the bird flu virus. Hands should be washed before and after handling poultry and eggs, and surfaces that have come in contact with the food should be cleaned thoroughly with hot soapy water. Cooked poultry should have an internal temperature of at least 165 F.
Masks and other respiratory protection should be used when caring for patients with bird flu. If a person has close contact with an infected patient, the exposed person may be offered oseltamivir in an attempt to prevent infection.
In 2007, the FDA licensed the first vaccine in the United States for humans against the highly pathogenic bird flu virus. The vaccine is made from inactivated viruses and does not contain any live viruses. It has been shown to stimulate the immune system to make antibodies against the bird flu virus that could presumably protect a person from the bird flu. The vaccine has been purchased by the federal government for inclusion within the CDC's Strategic National Stockpile. It is not available to the general public in part because the United States does not currently have a problem with the highly pathogenic strain of bird flu. Vaccine side effects include a sore arm, fatigue, or temporary muscle aches. The vaccine has not been tested in large numbers of patients, however, and there may be other side effects that have not yet been detected. The current vaccine is effective against the strain that has caused the large outbreaks of bird flu, but it may not be as effective against a newly mutated strain found in 2011.
Research on vaccines against influenza viruses is ongoing, and new developments such as a vaccine that is directed against the common and relatively unchanging antigens on the influenza viruses may lead to a vaccine that is protective against most if not all influenza viruses. If such research is successful, potential influenza outbreaks, including avian flu, may be reduced or prevented in the future.
Where can people find more information about bird flu?
The World Health Organization (http://www.who.int/csr/disease/avian_influenza/en/) provides current information about outbreaks and management of bird flu.
http://www.medicinenet.com/bird_flu/article.htm
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