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Bird Flu (Avian Flu)

Basic Information for Healthcare Workers

Susan Walters Schmid, BA, MA, PhD candidate

Courses are approved by CECBEMS and the California Emergency Medical Services Authority. For more information about accreditation, click here. This course is appropriate for EMTs, paramedics, and first responders.

The information in this course is taken primarily from Centers for Disease Control and Prevention: Influenza—Protect Yourself and Your Loved Ones, Avian Influenza (Bird Flu) and was updated June, 2006. For more information about avian influenza, go to http://www.cdc.gov/flu/avian. Learning objectives and post test were prepared by Susan Walters Schmid.

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, and some domesticated birds—including chickens, ducks, and turkeys—can become infected and even die.

INFLUENZA TYPES A, B, AND C

There are three types of influenza viruses: A, B, and C. Influenza type A viruses can infect people, birds, pigs, horses, seals, whales, and other animals, but wild birds are the natural hosts for these viruses. Influenza type A viruses are divided into subtypes based on two proteins on the surface of the virus. These proteins are called hemagglutinin (HA) and neuraminidase (NA).

There are sixteen known HA subtypes and nine known NA subtypes of influenza A viruses. Many different combinations of HA and NA proteins are possible, each combination representing a different subtype. Subtypes of influenza A virus are named according to their HA and NA surface proteins. For example, an "H7N2 virus" designates an influenza A subtype that has an HA 7 protein and an NA 2 protein. Similarly an "H5N1" virus has an HA 5 protein and an NA 1 protein.

Humans can be infected with influenza types A, B, and C. Only influenza A viruses infect birds, and all known subtypes of influenza A viruses can infect birds.

AVIAN INFLUENZA

Avian influenza viruses (type A) circulate among birds worldwide. Certain birds, particularly water birds, act as hosts for influenza viruses by carrying the virus in their intestines and shedding it. 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. Fecal-to-oral transmission is the most common mode of spread between birds.

Domesticated 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. People, vehicles, and other inanimate objects such as cages can be vectors for the spread of influenza virus from one farm to another. When this happens, avian influenza outbreaks can occur among poultry.

Infection with avian influenza viruses in domestic poultry causes two main forms of disease that are distinguished by low and high extremes of virulence—low pathogenic avian influenza (LPAI) or highly pathogenic avian influenza (HPAI). HPAI viruses can kill 90 to 100% of infected chickens, whereas LPAI viruses cause less severe or no illness if they infect chickens. It is not certain how the distinction between "low pathogenic" and "highly pathogenic" is related to the risk of disease in people. Because some LPAI viruses can evolve into HPAI viruses, animal health officials closely monitor outbreaks of those LPAI.

Other Wild and Domesticated Animals

In addition to humans and birds, we know that pigs, tigers, leopards, ferrets, and domestic cats can be infected with avian influenza (H5N1) viruses. In addition, in early March 2006, Germany reported avian flu infection in a stone marten (a weasel-like mammal). The avian influenza (H5N1) virus that emerged in Asia in 2003 is evolving, and it is possible that other mammals may be susceptible to infection as well.

While domestic cats are not usually susceptible to influenza type A infection, it is known that they can become infected and die with avian influenza A (H5N1). During the H5N1 outbreak that occurred from 2003 to 2004 in Asia, there were a few unofficial reports of fatal infections in domestic cats. Studies carried out in the Netherlands and published in 2004 showed that housecats could be infected with avian flu and could spread the virus to other housecats. In February 2006, Germany reported that a domestic cat had died from influenza A (H5N1) infection.

There is no evidence to date that cats can spread H5N1 to humans. No cases of avian influenza in humans have been linked to exposure to sick cats, and no outbreaks among populations of cats have been reported. All of the H5N1 infections in cats reported to date appear to have been associated with outbreaks in domestic or wild birds and acquired through ingestion of raw meat from an infected bird. 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.

Information is too limited to determine definitively whether dogs are susceptible to avian flu; however, as long as there is no influenza A (H5N1) in the United States, there is no risk of a U.S. dog becoming infected with this disease. The American Veterinary Medical Association (AVMA) maintains a website with current information. The CDC, USDA, and the AVMA, along with other veterinary associations, are working cooperatively on this issue and healthcare professionals can keep abreast of information through these agencies.

TRANSMISSION TO HUMANS

Usually, "avian influenza virus" refers to influenza A viruses found chiefly in birds and less commonly in pigs, but infections with these viruses can occur in humans. "Human influenza virus" usually refers to those subtypes that spread widely among humans. The only subtypes of influenza A virus that normally infect people, and are known to be currently circulating, are influenza A subtypes H1N1, H1N2, and H3N2. 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.

The risk from avian influenza is generally low for most people because the viruses occur mainly among birds and do not usually infect humans. However, more than 200 human cases of avian influenza infection have been reported since 1997. Most cases of avian influenza infection in humans have resulted from direct or close contact with infected poultry (eg, domesticated chicken, ducks, and turkeys) or surfaces contaminated with secretion/excretions from infected birds.

Thus during an outbreak of avian influenza among poultry, there is a possible risk to people who have contact with infected birds or contaminated surfaces. The spread of avian influenza viruses from one ill person to another has been reported very rarely, and transmission has not been observed to continue beyond one person.

Two main risks to human health from avian influenza are:

• The risk of direct infection when the virus passes from the infected bird to humans, sometimes resulting in severe disease
• 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.

Influenza Strains

Subtypes of influenza A virus are further characterized into strains. There are many different strains of influenza A subtypes. New strains of influenza viruses appear and replace older strains. When a new strain of human influenza virus emerges, antibody protection that may have developed after infection or vaccination with an older strain may not provide protection against the new strain.

Drift and Shift

Influenza viruses can change in two different ways. One type is called antigenic drift, which occurs through small changes in the virus that happen continually over time. Antigenic drift produces new virus strains that may not be recognized by antibodies to earlier influenza strains. This process works as follows: A person infected with a particular flu virus strain develops antibodies against that virus. As newer virus strains appear, the antibodies against the older strains no longer recognize the "newer" virus, and infection with a new strain can occur. This is one of the reasons people can get the flu more than once.

The other type of change is called antigenic shift. Antigenic shift is an abrupt, major change in the influenza A viruses, resulting in a new influenza virus that can infect humans and has a hemagglutinin protein or hemagglutinin and neuraminidase protein combination that has not been seen in humans for many years.

Antigenic shift results in a new influenza A subtype. If a new subtype of influenza A virus is introduced into the human population, and most people have little or no protection against the new virus, and if the virus can spread easily from person to person, a pandemic (worldwide spread) may occur.

Influenza viruses are changing by antigenic drift all the time, but antigenic shift happens only occasionally. Influenza type A viruses undergo both kinds of changes.

Re-Assortment and Transmission

There are substantial genetic differences between the subtypes of influenza A viruses that typically infect both people and birds. Within these subtypes there are also different strains. Influenza A viruses normally seen in one species sometimes can cross over and cause illness in another species.

Although it is unusual for people to get influenza virus infections directly from animals, sporadic human infections and outbreaks caused by certain avian influenza A viruses and pig influenza viruses have been reported. These sporadic human infections and outbreaks, however, rarely result in sustained transmission among humans.

Avian influenza A viruses may be transmitted from animals to humans in two main ways:

• Directly from birds or from avian virus-contaminated environments to people.
• Through an intermediate host, such as a pig.

Influenza A viruses have eight separate gene segments. The segmented genome allows influenza A viruses from different species to mix and create a new influenza A virus if viruses from two different species infect the same person or animal. For example, if a pig were infected with a human influenza A virus and an avian influenza A virus at the same time, the new replicating viruses could mix existing genetic information (re-assortment) and produce a new virus that had most of the genes from the human virus, but a hemagglutinin and/or neuraminidase from the avian virus.

The resulting new virus might then be able to infect humans and spread from person to person, but it would have surface proteins (hemagglutinin and/or neuraminidase) not previously seen in influenza viruses that infect humans. This type of major change in the influenza A viruses would be an example of antigenic shift. If this new virus caused illness in people and could be transmitted easily from person to person, an influenza pandemic could occur.

It is possible that the process of genetic re-assortment could occur in a human who is co-infected with avian influenza A virus and a human strain of influenza A virus. The genetic information in these viruses could re-assort to create a new virus with a hemagglutinin from the avian virus and other genes from the human virus.

Theoretically, influenza A viruses with a hemagglutinin against which humans have little or no immunity that have re-assorted with a human influenza virus are more likely to result in sustained human-to-human transmission and pandemic influenza. Therefore, careful evaluation of influenza viruses recovered from humans who are infected with avian influenza is very important to identify re-assortment if it occurs.

SYMPTOMS, DIAGNOSIS, PREVENTION, AND TREATMENT
IN HUMANS

Symptoms of avian influenza in humans have ranged from typical human influenza-like symptoms (fever, cough, sore throat, and muscle aches) to eye infections (conjunctivitis), pneumonia, acute respiratory distress, viral pneumonia, and other severe and life-threatening complications. The symptoms of avian influenza may depend on which specific virus subtype and strain caused the infection.

A laboratory test is needed to confirm avian influenza in humans. Studies done in laboratories suggest that 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 medications, so they may not always work.

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, oseltamivir (Tamiflu) and zanamivir (Relenza), may work to treat influenza caused by H5N1 virus, but additional studies are needed to demonstrate their effectiveness.

Because of increased resistance to the adamantanes, the Centers for Disease Control (CDC) issued a Health Alert Network (HAN) notice on January 14, 2006, recommending against the use of these drugs (amantadine and rimantadine) for the treatment or prophylaxis of flu for the duration of the 2005–2006 flu season. Healthcare practitioners should ensure that the appropriate person(s) at their agencies are subscribed to both the CDC Health Alert Network and their state’s HAN, and that information from those networks is distributed as appropriate.

There currently is no commercially available vaccine to protect humans against the H5N1 virus being seen in Asia and Europe. However, vaccine development efforts are under way. Research studies to test a vaccine to protect humans against H5N1 virus began in April 2005, and a series of clinical trials is ongoing. More information is available from the National Institutes of Health vaccine website and the World Health Organization avian flu website (listed in Resources).

Currently, wearing a mask is not recommended for routine use (eg, in public) for preventing influenza exposure. In the United States, disposable surgical and procedure masks have been widely used in healthcare 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.

There is no evidence that properly cooked poultry or eggs can be a source of infection for avian influenza viruses. 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 is still in place.

THE WORLD SITUATION

Outbreaks of avian influenza H5N1 occurred among poultry in eight countries in Asia—Cambodia, China, Indonesia, Japan, Laos, South Korea, Thailand, and Vietnam—during late 2003 and early 2004. At that time, more than 100 million birds in the affected countries either died from the disease or were killed in order to try to control the outbreaks. By March 2004 the outbreak was reported to be under control.

Beginning in June 2004, however, new outbreaks of influenza H5N1 among poultry and wild birds were reported in Asia. Since that time, the virus has spread. Reports of H5N1 infection in wild birds in Europe began in mid-2005. In early 2006, influenza A H5N1 infection in wild birds and poultry were reported in Africa and the Near East.

Human cases of influenza A (H5N1) infection have been reported on all populated continents except North and South America. For the most current information about avian influenza and cumulative case numbers, see the World Health Organization Avian Influenza website (listed in Resources).

H5N1 virus does not usually infect people, but more than 200 human cases have been reported. Most of these cases have occurred in people having direct or close contact with infected poultry or contaminated surfaces; however, a few cases of human-to-human spread of H5N1 have occurred. In late May 2006 it was reported that all the genetically related members of one family in Indonesia had died, while family members not related by blood (eg, in-laws) survived.

Of the few avian influenza viruses that have crossed the species barrier to infect humans, H5N1 has caused the largest number of detected cases of severe disease and death in humans. In the current outbreaks in Asia and Europe, more than half of those infected with the virus have died. Most cases have occurred in previously healthy children and young adults. However, it is possible that the only cases currently being reported are those in the most severely ill people, and that the full range of illness caused by the H5N1 virus has not yet been defined.

INFECTION CONTROL FOR HEALTHCARE WORKERS

The Centers for Disease Control (CDC) has issued interim recommendations, based on what are deemed optimal precautions, for protecting individuals involved in the care of patients with highly pathogenic avian influenza and for reducing the risk of viral re-assortment (ie, mixing of genes from human and avian viruses).

The ability of low-pathogenic avian influenza viruses to cause infection and serious disease is less well established, but appears to be lower than that of highly pathogenic viruses based on available information. Nonetheless, it is considered prudent to take precautions to the extent feasible when caring for patients with known or possible avian influenza.

Rationale for Enhanced Precautions

Human influenza is thought to transmit primarily via large respiratory droplets. Standard Precautions plus Droplet Precautions are recommended for the care of patients infected with human influenza. However, given the uncertainty about the exact modes by which avian influenza may first transmit between humans, additional precautions may be prudent for healthcare workers involved in the care of patients with documented or suspected avian influenza. The rationale for the use of additional precautions for avian influenza as compared with human influenza include the following:

• The risk of serious disease and increased mortality from highly pathogenic avian influenza may be significantly higher than from infection by human influenza viruses.
• Each human infection represents an important opportunity for avian influenza to further adapt to humans and gain the ability to transmit more easily among people.
• Although rare, human-to-human transmission of avian influenza may be associated with the possible emergence of a pandemic strain.

Recommendations for Avian Influenza

All patients who present to a healthcare setting with fever and respiratory symptoms should be managed according to recommendations for respiratory hygiene and cough etiquette and questioned about their recent travel history.

Patients with a history of travel within ten days to a country with avian influenza activity who are hospitalized with a severe febrile respiratory illness, or are otherwise under evaluation for avian influenza, should be managed using isolation precautions identical to those recommended for patients with known Severe Acute Respiratory Syndrome (SARS). These include:

• Standard Precautions
• Pay careful attention to hand hygiene before and after all patient contact or contact with items potentially contaminated with respiratory secretions.
• Contact Precautions
• Use gloves and gown for all patient contact.
• Use dedicated equipment such as stethoscopes, disposable blood pressure cuffs, disposable thermometers, etc.
• Eye protection (ie, goggles or face shields)
• Wear when within three feet of the patient.
• Airborne Precautions
• Place the patient in an airborne isolation room (AIR). Such rooms should have monitored negative air pressure in relation to corridor, with 6 to 12 air changes per hour (ACH), and exhaust air directly outside or have recirculated air filtered by a high-efficiency particulate air (HEPA) filter. If an AIR is unavailable, contact the healthcare facility engineer to assist or use portable HEPA filters to augment the number of ACH.
• Use a fit-tested respirator, at least as protective as a National Institute of Occupational Safety and Health (NIOSH)–approved N-95 filtering facepiece (ie, disposable) respirator, when entering the room.

Additional information regarding these and other healthcare isolation precautions is available on the CDC website. These precautions should be continued for fourteen days after onset of symptoms or until either an alternative diagnosis is established or diagnostic test results indicate that the patient is not infected with influenza A virus. Patients managed as outpatients or hospitalized patients discharged before fourteen days with suspected avian influenza should be isolated in the home setting on the basis of principles outlined for the home isolation of SARS patients.

Vaccination of Healthcare Workers

Healthcare workers involved in the care of patients with documented or suspected avian influenza should be vaccinated with the most recent seasonal human influenza vaccine. In addition to providing protection against the predominant circulating influenza strain, this measure is intended to reduce the likelihood of a healthcare worker's being co-infected with human and avian strains where genetic rearrangement could take place, leading to the emergence of potential pandemic strain.

Monitoring of Healthcare Workers

Healthcare workers need to be vigilant for the development of fever, respiratory symptoms, and/or conjunctivitis (ie, eye infections) for one week after last exposure to avian influenza–infected patients. Healthcare workers who become ill should seek medical care and, prior to arrival, notify their healthcare provider that they may have been exposed to avian influenza. In addition, employees should notify occupational health and infection control personnel at their facility.

With the exception of visiting a healthcare provider, healthcare workers who become ill should be advised to stay home until twenty-four hours after resolution of fever, unless an alternative diagnosis is established or diagnostic tests are negative for influenza A virus. While at home, ill persons should practice good respiratory hygiene and cough etiquette to lower the risk of transmission of virus to others.

STAYING INFORMED, BEING PREPARED (DHHS, 2006)

What Is a Pandemic?

A pandemic is a global disease outbreak. A flu pandemic occurs when a new influenza virus emerges for which people have little or no immunity, and for which there is no vaccine. The disease spreads easily person-to-person, causes serious illness, and can sweep across a country and around the world in very short time.

It is difficult to predict when the next influenza pandemic will occur or how severe it will be. Wherever and whenever a pandemic starts, everyone around the world is at risk. Countries might, through measures such as border closures and travel restrictions, delay arrival of the virus, but they cannot stop it.

Health professionals are concerned that the continued spread of a highly pathogenic avian H5N1 virus across eastern Asia and other countries represents a significant threat to human health. The H5N1 virus has raised concerns about a potential human pandemic because:

• It is especially virulent.
• It is being spread by migratory birds.
• It can be transmitted from birds to mammals and in some limited circumstances to humans.
• Like other influenza viruses, it continues to evolve.

Potential Impact of a Pandemic

A pandemic may come and go in waves, each of which can last for 6 to 8 weeks. An especially severe influenza pandemic could lead to high levels of illness, death, social disruption, and economic loss. Everyday life would be disrupted because so many people in so many places become seriously ill at the same time. Impacts can range from school and business closings to the interruption of basic services such as public transportation and food delivery.

A substantial percentage of the world's population will require some form of medical care. Healthcare facilities can be overwhelmed, creating a shortage of hospital staff, beds, ventilators and other supplies. Surge capacity at nontraditional sites such as schools may need to be created to cope with demand.

The need for vaccine is likely to outstrip supply and the supply of antiviral drugs is also likely to be inadequate early in a pandemic. Difficult decisions will need to be made regarding who gets antiviral drugs and vaccines.

Death rates are determined by four factors:

• Number of people who become infected
• Virulence of the virus
• Underlying characteristics and vulnerability of affected populations
• Availability and effectiveness of preventive measures

Preparation

The United States has been working closely with other countries and the World Health Organization (WHO) to strengthen systems to detect outbreaks of influenza that might cause a pandemic. The effects of a pandemic can be lessened if preparations are made in advance. The Department of Health and Human Services and other federal agencies are providing funding, advice, and other support to states to assist with pandemic planning and preparation. Information on international as well as state/federal planning and cooperation, including links to state pandemic plans, is available at http://www.pandemicflu.gov. Healthcare professionals should familiarize themselves with the material there and visit the website frequently for updated information.

Education and outreach are critical to preparing for a pandemic. Understanding what a pandemic is, what needs to be done at all levels to prepare for pandemic influenza, and what could happen during a pandemic helps people to make informed decisions. Well-informed healthcare professionals may help others in their communities in this endeavor.

Pandemic influenza planning checklists are available at the pandemic flu website. These checklists address three areas: creating a structure for planning and decision making, developing a written pandemic influenza plan, and elements of an influenza pandemic plan. Individual checklists in downloadable format are available for the following: state and local government, business, individuals and families, schools, healthcare providers (of all types), and faith-based and community organizations.

Posted December 14, 2005

Expires August 1, 2008

Copyright © 2005 Wild Iris Medical Education. All rights reserved.

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