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Officials Monitoring, Preparing for Possible Avian Flu

Breaking News - October 2005 - Week 3

(Oct 19, 2005)

Healthcare in  the News

-- With concern mounting over the threat posed by bird flu, federal officials recently met with executives of major vaccine manufacturers to discuss the development of enough vaccine to counter a possible pandemic.

Picture of people working in a lab

A pandemic is an epidemic over a wide geographic area which affects a large proportion of the population.

According to the Centers for Disease Control and Prevention (CDC), bird flu is an infection caused by avian (bird) influenza (flu) viruses. These flu viruses occur naturally among birds. Wild birds worldwide carry the viruses, but usually do not get sick from them.

However, bird flu is very contagious among birds and can make some domesticated birds, including chickens, ducks, and turkeys, very sick and kill them.

Bird flu viruses do not usually infect humans, the CDC states, but several cases of human infection with bird flu viruses have occurred since 1997.

The potential threat posed by bird, or avian, flu has been compared to that of the Spanish flu of 1918-19, which killed 50 million people worldwide, including more than 500,000 in the US.

In fact, US researchers announce that the bird flu strain that is emerging in the Far East shares some of the same genetic characteristics as the flu virus that caused the 1918 pandemic.

The current bird flu, called H5N1, is spreading throughout Asia and has reached Russia, Turkey, and Romania. So far infection has been mostly confined to millions of birds, but has caused the deaths of an estimated 65 people in Asia.

Up till now, transmission of the disease from person to person has been limited, although most experts agree it is only a matter of time before that process becomes easier.

The CDC states that the current risk to Americans from the H5N1 bird flu outbreak in Asia is low. The strain of H5N1 virus found in Asia has not been found in the US. There have been no human cases of H5N1 flu in the US.

It is possible that travelers returning from affected countries in Asia could be infected. Since February 2004, medical and public health personnel have been watching closely to find any such cases.

"We are very focused on the potential for a pandemic outbreak of influenza," says Dr. Julie L. Gerberding, director of the CDC. "Most experts agree it's not a question of if, it's a question of when. The current H5 outbreak in Asia, we are taking it very seriously."

Vaccine Research Holds Promise

The US government is supporting the development of vaccines and attempting to stockpile the oral antiviral medication Tamiflu® (oseltamivir), which appears to be effective against the H5N1 strain in mice.

The US Food and Drug Administration (FDA) approved Tamiflu in 1999 for the treatment of Type A and B flu in adults whose symptoms do not last more than two days. Type A flu is the most common in the US.

While initial testing of an avian flu vaccine shows promise and clinical trials should be completed by the end of the year, questions remain about the vaccine's ability to protect large numbers of people, US researchers say.

Among the potential problems: The vaccine dose needs to be much higher than that given for other types of flu, according to Dr. John Treanor, who is the principal investigator of the vaccine tests being done at the University of Rochester.

"It seems to be a characteristic of the H5 vaccines that they require a higher dose to illicit an immune response than some other vaccines do,” Dr. Treanor explains. “Dose-related immune responses are being tested to get a feeling for what dose would be required. And then we need to see if anything could be done so lower doses could be used.”

Another expert, Dr. Stephen S. Morse, director of Columbia University Center for Public Health Preparedness, says, "We are concerned about avian flu. But the next pandemic could come from some other [virus] as yet not on our radar screen - an unanticipated influenza.”

Some trial batches of bird flu vaccine have been made by US researchers, Dr. Morse notes. "This was done to demonstrate the capability and make sure that all the pieces were in place in case we actually needed such a vaccine for human use."

However, Dr. Morse says that should bird flu become easily transmittable from person to person, a vaccine for that specific strain would have to be developed.

"Currently our vaccine capacity is limited,” he says. “So [developing a vaccine] depends on a number of things, including political will and timing.”

Factors needed to produce a vaccine quickly include swift recognition by health experts of a new flu strain and increased manufacturing ability, Dr. Morse says.

“We are headed in the right direction. I hope we have time to put the pieces in place."

Several Antivirals under Consideration

Many public health experts have pinned their hopes on the antiviral drug Tamiflu to help stem a potential pandemic caused by avian flu, but a new report reveals the virus can become resistant to Tamiflu in some patients.

According to the article, which appears in the medical journal Nature, a strain of the H5N1 flu virus that infected a Vietnamese girl in February is resistant to Tamiflu. Although the girl recovered, the finding raises concerns that Tamiflu may not be enough to fight a potential H5N1 pandemic.

While the strain of the virus was resistant to Tamiflu, when the research team tested the virus in animals they found that it was still sensitive to another antiviral medication called RelenzaTM (zanamivir).

Given that, "It could be useful to stockpile zanamivir, as well as oseltamivir, in the event of an H5N1 influenza pandemic," the authors conclude.

One expert says this mutation of the virus was not unexpected, and warned against the overuse of Tamiflu.

"This isn't terribly surprising," says Dr. Arnold S. Monto, a professor of epidemiology at the University of Michigan School of Public Health. "We know that you can get a mutation in a small number of people who are treated."

Dr. Monto comments that there is no guarantee that Relenza will be effective against the avian flu, because Relenza is not designed to treat a systemic infection such as the avian flu.

"If, when the virus transfers from humans to humans, it stops being a systemic infection, then Relenza might be a realistic option," he says. "If it does not and we see an increased resistance to oseltamivir, then we've got a problem on our hands."

Given the potential resistance to Tamiflu, Dr. Monto remarks, "We need something else to use for a systemic infection."

Always consult your physician for more information.

For more information on health and wellness, please visit health information modules on this Web site.


CDC Defines Avian Flu

The Centers for Disease Control and Prevention (CDC) states that there are many different subtypes of type A flu viruses. All subtypes of flu A viruses can be found in birds.

However, when “bird flu” viruses are discussed, this refers to those flu A subtypes that continue to occur mainly in birds. They do not usually infect humans, even though they can do so.

Symptoms of bird flu in humans have ranged from typical flu-like symptoms (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 bird flu may depend on which virus caused the infection.

Studies suggest, states the CDC, that the prescription medications approved for human flu viruses would work in preventing bird flu infection in humans.

However, flu viruses can become resistant to these medications, so they may not always work.

The risk from bird flu is generally low for most people because the viruses occur mainly among birds and do not usually infect humans.

However, during an outbreak of bird flu among poultry (domesticated chicken, ducks, turkeys), there is a possible risk to people who have contact with infected birds or surfaces that have been contaminated with excretions from infected birds.

The current outbreak of avian influenza A (H5N1) among poultry in Asia is an example of a bird flu outbreak that has caused human infections and deaths. In such situations, people should avoid contact with infected birds or contaminated surfaces, and should be careful when handling and cooking poultry.

The H5N1 virus does not usually infect humans, according to the CDC. In 1997, however, the first case of spread from a bird to a human was seen during an outbreak of bird flu in poultry in Hong Kong.

Most recently, human cases of H5N1 infection have occurred in Thailand, Vietnam, and Cambodia during large H5N1 outbreaks in poultry.

Most of these cases occurred from contact with infected poultry or contaminated surfaces; however, it is thought that a few cases of human-to-human spread of H5N1 have occurred.

So far, spread of H5N1 virus from person to person has been rare and spread has not continued beyond one person.

However, because all influenza viruses have the ability to change, scientists are concerned that the H5N1 virus could one day be able to infect humans and spread easily from one person to another.

The H5N1 virus currently infecting birds in Asia that has caused human illness and death is resistant to amantadine and rimantadine, two antiviral medications commonly used for influenza.

Two other antiviral medications, oseltamivir and zanamivir, may work to treat flu caused by the H5N1 virus, though studies still need to be done to prove that they work, the CDC states.

There currently is no vaccine to protect humans against the H5N1 virus that is being seen in Asia. However, vaccine development efforts are under way.

Research studies to test a vaccine to protect humans against H5N1 virus began in April, 2005.

Always consult your physician for a diagnosis.


Online Resources

(Our Organization is not responsible for the content of Internet sites.)

Centers for Disease Control and Prevention (CDC)

CDC on Avian Flu

National Institutes of Health (NIH)

Nature

US Food and Drug Administration (FDA)

World Health Organization

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