Avian Influenza

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What is avian influenza?

Avian influenza is caused by influenza A viruses that occur naturally among birds. There are different subtypes of these viruses because of changes in certain proteins (hemagglutinin [HA] and neuraminidase [NA]) on the surface of the influenza A virus and the way the proteins combine.

Each combination represents a different subtype. All known subtypes of influenza A viruses can be found in birds. The avian flu currently of concern is the H5N1 subtype.

Are there vaccination and treatment options for H5N1 virus in humans?

There currently is no commercially available vaccine to protect humans against H5N1 virus that is being seen in Asia, Europe, and Africa. A pandemic vaccine cannot be produced until a new pandemic influenza virus emerges and is identified.

The U.S. Department of Health and Human Services (HHS), through its National Institute of Allergy and Infectious Diseases (NIAID), is addressing the problem in a number of ways. These include the development of pre-pandemic vaccines based on current lethal strains of H5N1, collaboration with industry to increase the Nation's vaccine production capacity, and seeking ways to expand or extend the existing supply. We are also doing research in the development of new types of influenza vaccines.

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.

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.

What are the symptoms of avian influenza in humans?

People infected with the current strand of the avian virus (H5N1) have shown everything from typical human influenza-like symptoms (fever, cough, sore throat, and muscle aches) to pneumonia, severe respiratory diseases, and other life-threatening complications. Symptoms of avian influenza may depend on which specific virus subtype and strain caused the infection.

Could terrorists spread the avian influenza viruses to create a worldwide pandemic?

Experts believe it highly unlikely that a pandemic influenza virus could be created by terrorists. Developing a pandemic influenza virus would require extraordinary scientific skill as well as sophisticated scientific equipment and other resources.

Three conditions must be met for a pandemic to start: 1) a new influenza virus subtype must emerge for which there is little or no human immunity; 2) it must infect humans and cause illness; and 3) it must spread easily and sustainably (continue without interruption) among humans.

What changes are needed for H5N1 or another avian influenza virus to cause a pandemic?

The H5N1 virus in Asia, Europe, and Africa meets the first two conditions: it is a new virus for humans (H5N1 viruses have never circulated widely among people), and it has infected a growing number of people, killing over half of those known to have been infected. However, the third condition, the establishment of efficient and sustained human-to-human transmission of the virus, has not occurred. For this to take place, the H5N1 virus would need to improve its transmissibility among humans.

What other strategies will help protect humans?

In the event of a pandemic, certain public health measures may be important to help contain or limit the spread of infection as effectively as possible. The following actions could include:

* treating sick and exposed people with antivirals;

* isolating sick people in hospitals, homes, or other facilities;

* identifying and quarantining exposed people;

* closing schools and workplaces as needed;

* canceling public events; and

* restricting travel.

In addition, people should protect themselves by:

* washing hands frequently with soap and water;

* staying away from people who are sick; and

* staying home if sick.

What are the concerns about avian influenza A (H5N1) outbreaks in Asia, Europe, the Near East, and Africa?

There is concern that the H5N1 virus could undergo genetic changes that would result in its ability to be easily transmitted between humans. Since the general population has not been exposed to this H5N1 influenza virus strain before, a mutation leading to sustained human-to-human transmission could cause an influenza pandemic.

Although it is not predictable when the next influenza pandemic will occur and what influenza virus strain may cause it, the continued and expanded spread of a highly pathogenic avian H5N1 virus that first began spreading throughout Asia in 2003 represents an important public health threat.

Human influenza A (H5N1) infections were first recognized in 1997 when this virus infected 18 people in Hong Kong, causing 6 deaths. In 2003, a highly pathogenic avian influenza A H5N1 virus (commonly called H5N1 or HPAI H5N1), started spreading in poultry throughout Asia. This H5N1 virus strain has now caused widespread disease in domestic poultry in Asia, parts of Europe, the Near East, and Africa. It also is causing illness and death in a relatively small number of wild birds. In addition to infecting birds, the H5N1 virus has infected and killed other animals and in a small number of cases, it has infected and killed humans.

Illness caused by this H5N1 influenza virus is very rare among people. Since 2003, the World Health Organization (WHO) has confirmed more than 250 H5N1 human infections in 10 countries. The H5N1 virus does not infect humans easily, and if a person is infected, it is very difficult for the virus to spread to another person. However, when serious infections with this virus occur, more than half of the humans known to be infected with this H5N1 virus have died. The majority of people infected with the virus have had direct contact with infected poultry.

The H5N1 virus has raised concerns about a potential human pandemic because:

* The virus is widespread in poultry in many countries in Asia and has spread to parts of Europe, the Near East, and Africa;

* The virus has been transmitted from birds to mammals and in some limited circumstances to humans who had close contact with infected poultry;

* Some wild birds and domestic ducks have become infected without showing symptoms and may be carriers or act as viral reservoirs able to infect domestic poultry species;

* A limited number of instances of probable human-to-human transmission has been reported, although none appears to have spread in a sustained way; and

* Genetic studies confirm that H5N1 influenza viruses, like other influenza viruses, continue to evolve.

Is influenza A (H5N1) virus the only avian influenza virus of concern regarding a pandemic?

Although highly pathogenic H5N1 currently poses a pandemic threat, other avian influenza A subtypes have infected people in recent years. For example, in 1999, H9N2 infections were identified in Hong Kong; in 2003, H7N7 infections occurred in the Netherlands and in 2004, H7N3 infections occurred in Canada. These examples of other avian influenza viruses that have infected humans demonstrate the potential of an influenza virus to evolve into a pandemic strain.

How do people become infected with avian influenza viruses?

Most cases of H5N1 avian influenza infection in humans have resulted from direct or close contact with infected poultry (e.g., domesticated chicken, ducks, and turkeys) or surfaces possibly contaminated from feces of infected birds. For a pandemic of influenza to occur, avian influenza must mutate/change to be able to be passed easily from person to person. A pandemic of influenza can arise from changes that occur in certain kinds of highly pathogenic avian influenza but no one knows when or even if this will happen. Today, there have been no reported cases of sustained human-to-human transmission of avian flu.

Has the highly pathogenic avian influenza (HPAI) H5N1 virus been detected in migratory birds in the United States?

No. The highly pathogenic avian influenza (HPAI) H5N1 virus has not yet been detected in wild birds or domestic poultry on the North American continent. Low pathogenic forms of H5 and H7 have occurred in both domestic and wild birds in North America and around the world for decades. Researchers do not know what causes a fairly benign H5 or H7 strain to change into a strain that is highly pathogenic. Should the HPAI H5N1 virus be detected in the United States, it does not signal the start of a human pandemic. Not until the HPAI H5N1 virus becomes easily transferred from person to person would a human pandemic begin.

Is it safe to eat raw eggs?

Eggs from infected poultry could also be contaminated with the virus and therefore care should be taken in handling eggs or raw egg products. Commercial mayonnaise, dressings, and sauces that contain pasteurized eggs are safe to eat. The Food and Drug Administration (FDA) discourages the consumption of eggs that have not been adequately cooked. FDA advises consumers to avoid eating or tasting foods that may contain raw or lightly cooked eggs, such as:

* raw batter, filling, or cookie dough made with raw eggs;

* eggnog and other egg-fortified beverages that are not thoroughly cooked; and

* homemade and fresh-made dressings and sauces made with raw eggs such as Caesar salad dressing, Bearnaise sauce, Hollandaise sauce, Aioli sauce, mayonnaise; homemade ice cream; mousse; meringue; or tiramisu.

What would be the impact of a avian influenza pandemic?

A pandemic may come and go in waves, each of which can last for six to eight 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. Health care facilities can be overwhelmed, creating a shortage of hospital staff, beds, ventilators and other supplies. Surge capacity at non-traditional 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: the number of people who become infected, the virulence of the virus, the underlying characteristics and vulnerability of affected populations and the availability and effectiveness of preventive measures.

Source: National Institutes of Health

BCM, Rice scientists map flu's chemical key

The research, which appears this week in the Proceedings of the National Academy of Science (PNAS) Online Early Edition, was conducted on a strain of the influenza B virus initially isolated from Hong Kong. Unlike strains of influenza A -- which include bird flu, swine flu and others -- influenza B affects only humans.

"The big question is, 'What would it take for the bird flu to change and start killing us"'" said research co-author Jianpeng Ma, a structural biologist who holds joint appointments at both BCM and Rice. "Since flu B is a distant relative of flu A, the fewer common features among them would allow identifying the critical parts required for infecting humans."

The research is based on a more than six years of painstaking experiments by lead author Qinghua Wang, assistant professor of biochemistry and molecular biology at BCM. The experiments focused on a protein called hemagglutinin (HA), the chemical key that allows flu viruses to attach to target cells and infect them with viral DNA. There are 16 HA proteins, but only flu B and H1, H2 and H3 of flu A are found in human-transmissible strains. Scientists know H5, the HA key used by bird flu, is very similar to the chemical keys used by human strains of flu A. Like all proteins, the HA keys consist of a precise sequence of amino acids.

"In terms of sequence, there is only a 25 percent overlap between HA proteins for type A and type B," Ma said. "But in terms of function, the two are remarkably similar.

Wang said, "It would be better if there were more differences. The similarities suggest that only minor mutations are needed for bird flu to become transmissible to human."

Scientists know the precise 3D structure of several HA keys for flu A, but Wang and Ma's work represents the first mapping of an HA key for flu B. Currently, Ma and Wang are working out the precise molecular mutations that will be required for bird flu's HA to change into a human transmissible form.

Keywords: Avian Flu, Avian Influenza, Bird Flu, Rice University.

This article was prepared by Pharma Business Week editors from staff and other reports. Copyright 2007, Pharma Business Week via NewsRx.com.