Avian influenza is an infection caused by avian (bird) influenza (flu) viruses. These influenza viruses occur naturally among birds. Wild birds worldwide carry the viruses in their intestines, but usually do not get sick from them. However, avian influenza is very contagious among birds and can make some domesticated birds, including chickens, ducks, and turkeys, very sick and kill them.
Infected birds shed influenza virus in their saliva, nasal secretions, and feces. Susceptible birds become infected when they have contact with contaminated secretions or excretions or with surfaces that are contaminated with secretions or excretions from infected birds. Domesticated birds may become infected with avian influenza virus through direct contact with infected waterfowl or other infected poultry, or through contact with surfaces (such as dirt or cages) or materials (such as water or feed) that have been contaminated with the virus.
Infection with avian influenza viruses in domestic poultry causes two main forms of disease that are distinguished by low and high extremes of virulence. The “low pathogenic” form may go undetected and usually causes only mild symptoms (such as ruffled feathers and a drop in egg production). However, the highly pathogenic form spreads more rapidly through flocks of poultry. This form may cause disease that affects multiple internal organs and has a mortality rate that can reach 90-100% often within 48 hours.
Human infection with avian influenza viruses
There are many different subtypes of type A influenza viruses. These subtypes differ because of changes in certain proteins on the surface of the influenza A virus (hemagglutinin [HA] and neuraminidase [NA] proteins). There are 16 known HA subtypes and 9 known NA subtypes of influenza A viruses. Many different combinations of HA and NA proteins are possible. Each combination represents a different subtype. All known subtypes of influenza A viruses can be found in birds.
Usually, “avian influenza virus” refers to influenza A viruses found chiefly in birds, but infections with these viruses can occur in humans. The risk from avian influenza is generally low to most people, because the viruses do not usually infect humans. However, confirmed cases of human infection from several subtypes of avian influenza infection have been reported since 1997. Most cases of avian influenza infection in humans have resulted from contact with infected poultry (e.g., domesticated chicken, ducks, and turkeys) or surfaces contaminated with secretion/excretions from infected birds. The spread of avian influenza viruses from one ill person to another has been reported very rarely, and has been limited, inefficient and unsustained.
“Human influenza virus” usually refers to those subtypes that spread widely among humans. There are only three known A subtypes of influenza viruses (H1N1, H1N2, and H3N2) currently circulating among humans. It is likely that some genetic parts of current human influenza A viruses came from birds originally. Influenza A viruses are constantly changing, and they might adapt over time to infect and spread among humans.
During an outbreak of avian influenza among poultry, there is a possible risk to people who have contact with infected birds or surfaces that have been contaminated with secretions or excretions from infected birds.
Symptoms of avian influenza in humans have ranged from typical human influenza-like symptoms (e.g., fever, cough, sore throat, and muscle aches) to eye infections, pneumonia, severe respiratory diseases (such as acute respiratory distress), and other severe and life-threatening complications. The symptoms of avian influenza may depend on which virus caused the infection.
Studies done in laboratories suggest that some of the prescription medicines approved in the United States for human influenza viruses should work in treating avian influenza infection in humans. However, influenza viruses can become resistant to these drugs, so these medications may not always work. Additional studies are needed to demonstrate the effectiveness of these medicines.
Causes
Viruses belonging to the “A” type of influenza viruses cause avian influenza. Usually, the avian influenza virus only infects birds. However, sometimes the virus can mutate (undergo some chemical and genetic changes). These mutations can allow it to infect pigs or humans. Humans who have close contact with infected birds or pigs can then contract the virus. There is also concern that the virus can mutate sufficiently to allow it to be passed between humans.
The virus is not contracted through eating poultry, eggs, or pork products. It is currently passed through contact with the saliva, nasal secretions, or droppings of infected animals.
Risk Factors
The following factors increase your chances of developing avian influenza. If you have any of these risk factors, tell your doctor:
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Close contact with infected animals, such as:
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Recent travel to an area known to have cases of avian influenza, such as:
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Symptoms
If you experience any of these symptoms, do not assume it is due to avian influenza. Avian influenza cannot be diagnosed by symptoms alone, so a laboratory test is required. Avian influenza is usually diagnosed by collecting a swab from the nose or throat during the first few days of illness. This swab is then sent to a laboratory, where they will either look for avian influenza virus using a molecular test, or they will try to grow the virus. Growing avian influenza viruses should only be done in laboratories with high levels of protection. If it is late in the illness, it may be difficult to find an avian influenza virus directly using these methods. If this is the case, it may still be possible to diagnose avian influenza by looking for evidence of the body's response to the virus. This is not always an option because it requires two blood specimens (one taken during the first few days of illness and another taken some weeks later), and it can take several weeks to verify the results.These symptoms may be caused by other, less serious health conditions. If you experience any one of them, see your physician. Symptoms may include:
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Flu symptoms such as:
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Eye infections
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Pneumonia
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Acute respiratory distress syndrome
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Simultaneous failure of organs, such as kidney, liver, lungs, and heart
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Problems with blood clotting
What are the implications of avian influenza to human health?
Two main risks for human health from avian influenza are 1) the risk of direct infection when the virus passes from the infected bird to humans, sometimes resulting in severe disease; and 2) the risk that the virus – if given enough opportunities – will change into a form that is highly infectious for humans and spreads easily from person to person.
Does seasonal influenza vaccine protect against avian influenza infection in people?
No. Seasonal influenza vaccine does not provide protection against avian influenza.
Should I wear a surgical mask to prevent exposure to avian influenza?
Currently, wearing a mask is not recommended for routine use (e.g., in public) for preventing influenza exposure. In the United States, disposable surgical and procedure masks have been widely used in health-care settings to prevent exposure to respiratory infections, but the masks have not been used commonly in community settings, such as schools, businesses, and public gatherings.
Can I get avian influenza from eating or preparing poultry or eggs?
You cannot get avian influenza from properly handled and cooked poultry and eggs.
There currently is no scientific evidence that people have been infected with bird flu by eating safely handled and properly cooked poultry or eggs.
Most cases of avian influenza infection in humans have resulted from direct or close contact with infected poultry or surfaces contaminated with secretions and excretions from infected birds. Even if poultry and eggs were to be contaminated with the virus, proper cooking would kill it. In fact, recent studies have shown that the cooking methods that are already recommended by the U.S. Department of Agriculture (USDA) and the Food and Drug Administration (FDA) for poultry and eggs to prevent other infections will destroy influenza viruses as well.
So to stay safe, the advice is the same for protecting against any infection from poultry:
- Wash your hands with soap and warm water for at least 20 seconds before and after handling raw poultry and eggs.
- Clean cutting boards and other utensils with soap and hot water to keep raw poultry from contaminating other foods.
- Use a food thermometer to make sure you cook poultry to a temperature of at least 165 degrees Fahrenheit Consumers may wish to cook poultry to a higher temperature for personal preference.
- Cook eggs until whites and yolks are firm.
The U.S. government carefully controls domestic and imported food products, and in 2004 issued a ban on importation of poultry from countries affected by avian influenza viruses, including the H5N1 strain. This ban still is in place.
Diagnosis
Your doctor will ask about your symptoms and medical history, and perform a physical exam. The types of blood tests available at most clinics and hospitals will be able to identify the presence of an influenza virus, but most laboratories do not have the equipment necessary to specifically identify the virus that causes avian influenza. Samples are usually sent to the Centers for Disease Control in Atlanta, Georgia where the avian influenza virus can be identified.
Treatment
Talk with your doctor about the best treatment plan for you. Research is still being done to find an antiviral agent that works against the virus that causes avian influenza. Some antiviral agents (amantadine and rimantadine) are ineffective against the virus. Thus far, it appears that oseltamavir and zanamavir may work against the avian flu virus. The H5N1 virus that has caused human illness and death in Asia is resistant to amantadine and rimantadine, two antiviral medications commonly used for influenza. Two other antiviral medications, oseltamavir and zanamavir, would probably work to treat influenza caused by H5N1 virus, but additional studies still need to be done to demonstrate their effectiveness. Most H5N1 viruses that have caused human illness and death appear to be resistant to amantadine and rimantadine, two antiviral medications commonly used for treatment of patients with influenza. Two other antiviral medications, oseltamivir and zanamavir, would probably work to treat influenza caused by H5N1 virus, but additional studies are needed to demonstrate their current and ongoing effectiveness.
Prevention
To help reduce your chances of getting avian influenza, take the following steps:
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Avoid traveling to areas where there are avian influenza outbreaks.
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Avoid contact with potentially infected poultry or swine, such as at farms or open-air markets.
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Because egg shells may be contaminated with bird droppings, avoid eating raw eggs.
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Cooked poultry will not transmit the avian influenza virus, but raw poultry could be contaminated with bird droppings, saliva, or mucus. Cook poultry thoroughly, and carefully clean your hands and all cooking surfaces, utensils, and cutting boards.
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Use excellent handwashing techniques if you might be in an area where exposure to the avian influenza virus is possible
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Use a hand sanitizer if clean water is not available for washing.
What is the current risk that a cat in the United States will become infected with influenza A (H5N1)?
As long as there is no influenza A (H5N1) in the United States, there is no risk of a U.S. cat becoming infected with this disease. The virus circulating in Asia, Europe and Africa has not yet entered the United States.
RESOURCES:
Centers for Disease Control
http://www.cdc.gov
World Health Organization
http://www.who.int
CANADIAN RESOURCES:
Canadian Medical Association Journal
http://www.cmaj.ca
Health Canada
http://www.hc-sc.gc.ca
References:
Cohen J, Powderly WG. Infectious Diseases, 2nd ed. NY: Elsevier; 2004.
Weir E, Wong T, Gemmill T. Avian influenza outbreak: update. CMAJ. Mar 2, 2004; 170:785-786.
