News & Events

Avian flu: a dreadful possibility on the horizon

From the Massachusetts Nurse Newsletter
November/December 2004 Edition

By Chris Pontus, MS, RN, COHN-S
Associate Director, Health & Safety

Recently, I attended a flu workshop focused on increasing employee participation and deliverance of influenza vaccine in the workplace.

The program leader asked an interesting question: What is the difference between an epidemic and a pandemic? A nurse in the audience answered that an epidemic was a local incident and a pandemic episode was a global event.

The thought of a pandemic episode has not yet entered into most of our immediate and or long term planning efforts. As stated in a recent executive summary of the Department of Health and Human Services, the possibility of "an influenza pandemic has a greater potential to cause rapid increases in death and illness than virtually any other natural health threat."

Influenza generally results in seasonal epidemics causing 36,000 deaths annually. A pandemic or global epidemic occurs when there is a major change in the influenza virus so that most or all of the world’s population has never been exposed previously and is thus vulnerable to the virus.

The influenza "A" virus known to affect domesticated birds does not usually infect people. However, a subtype of the virus "H 5N1" is responsible for the first recorded case Avian flu: a dreadful possibility on the horizon of virus transferred to humans by direct birdto- human transmission. Ability of the virus to change creates a real potential threat for most of the world’s population simply because they have not yet been exposed.

The World Health Organization (WHO) compared a report on the recent outbreaks of avian flu with previous ones. The WHO stated that avian flu, until recently, was considered to be a rare disease and that most countries have had little or no experience with it, making it harder for them to currently deal with the disease.
The Occupational Health and Safety Administration recently posted Guidance for Protecting Workers Against Avian Flu on its Web site at www.hhs.gov/nvpo/pandemicplan/exec_summ.hmtl. The page also has links to the Centers for Disease Control and the World Health Organization. The following information was pulled from these aforementioned resources.

Background on the current outbreak
An outbreak of influenza A (H5N1), also know as "avian flu" or "bird flu," has been reported in several countries throughout Asia. Cases of avian influenza A (H5N1) in birds have been confirmed in Cambodia, China, Hong Kong, Indonesia, Japan, Laos, Pakistan, South Korea, Thailand, and Vietnam. Human cases of avian influenza have been reported in Thailand and Vietnam. During this outbreak investigation, it has not been determined that avian flu is spread from person to person. This strain of avian influenza A (H5N1) currently affecting Asia has not been found in the United States. The current outbreak of avian influenza has prompted the killing of more than 25 million birds in Asia.

In February 2004, different strains of avian flu were detected among several flocks of birds in the U.S. and state officials ordered the destruction of hundreds of thousands of birds. The avian influenza strain found in Delaware was (H7N2), in Pennsylvania the strain was (H2N2), and the (H5N2) strain was found in Texas. The strain found in Texas has been determined to be "highly pathogenic" to birds. However, the strain of avian influenza in Texas is not the same as the strain that is affecting Asia. There does not appear to be any connection between the illness in the flocks on the East Coast and the flock in Texas. Wild birds are the natural hosts for the virus. Avian flu viruses circulate among birds worldwide and are highly contagious among birds. It is also important to note that the United States annually imports an estimated 20,000 birds from countries with current avian influenza outbreaks, according to the U.S. Fish and Wildlife Service.

Background on influenza, avian flu Influenza is a category of viruses associated with acute (short), usually self-limited infections, whose symptoms are most commonly fever, muscle pain or aches, and cough. However, illness can be more severe based upon the properties of the virus, the patient’s age, pre-existing immunity status, or pre-existing medical conditions.

The influenza virus is described by a three-part naming system that includes the virus type, subtype and strain. There are three major types (A, B, C) and a number of subtypes which are classified based upon the surface coatings of the virus. These surface coatings determine whether the virus will affect humans, pigs, horses or birds, or more than one type of animal. Within a specific type and subtype of influenza, there are also important differences in the particular strain of virus. For example, the strain of influenza A (H5N1) that has affected birds and humans in much of Asia is not the same strain that is affecting birds in the U.S. or Pakistan.

Influenza viruses also change or mutate over time. "Scientists know that the avian and human influenza viruses can exchange genes when a person is simultaneously infected with viruses from both the common human influenza virus and the avian type.

This process of gene swapping inside the human body can give rise to a completely new subtype of the influenza virus to which few, if any, humans would have any natural immunity…If the new virus contains sufficient human flu virus genes, transmission directly from one person to another (instead of from birds to humans only) can occur." Some previous outbreak investigations documented limited human-to-human transmission of avian influenza. It is believed that most cases of avian influenza in humans have resulted from contact with infected poultry or contaminated surfaces.

In particular, influenza A (H5N1) has a documented tendency to acquire genes from viruses infecting other animals. There is particular cause for concern because this strain of influenza A (H5N1) is now spreading from birds (e.g., chickens, ducks, turkeys) to humans, and scientists are trying to determine if the virus is also spreading from human to human. Since this strain of influenza virus does not commonly infect humans, the general population may not have natural immunity to the virus. The current strain of influenza A (H5N1) that is transmitted from birds to humans is considered to be "highly pathogenic."

Routes of exposure to avian flu
Most human influenza infections are spread by virus-laden respiratory droplets that are expelled during coughing and sneezing. Influenza viruses range in size from 0.08 to 0.12 micrometers. They are carried in respiratory secretions as small-particle aerosols (less than 10 micrometers in diameter).

In an agricultural setting, animal manure containing influenza virus can contaminate dust and soil, causing infection when the contaminated dust is inhaled. Contaminated farm equipment, feed, cages, or shoes can carry the virus from farm to farm. The virus can also be carried on the bodies and feet of animals, such as rodents. The virus can survive, at cool temperatures, in contaminated manure for at least three months. In water, the virus can survive for up to four days at 72º F and more than 30 days at 32º F. For the highly pathogenic form (of influenza A), studies have shown that a single gram of contaminated manure can contain enough virus to infect one million birds.

In a food handling/preparation setting, there is also some concern that avian influenza could be transmitted from uncooked birds or bird products. The World Health Organization has also reported a study that found avian influenza A (H5N1) in imported frozen duck meat. Eggs from infected poultry could also be contaminated with the virus.

Additional sources of information
There are other federal agencies and international organizations that have further resources on avian flu.

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