Pandemic Evolution?

The United States is braced to join the 51 or more nations coping with a virulent strain of bird flu. Will the H5N1 virus remain an avian disease—or will it make the leap to human transmission?

There are some words—terrorism or cancer, for instance—that evoke such fear, we try not to breathe them out loud, as if speaking the name of those evils could increase their capacity to harm us.

Ironically, it's the taboo quality of these words that make them appealing choices for headlines. They seize our attention and quicken our pulse: We can't look away. Fear drives our thirst for information.

"Pandemic"—the worldwide outbreak of a disease—is a prime example of this category. Though few are alive who remember the flu pandemic of 1918-19, its specter still haunts us. The deadliest of the 10 flu pandemics that have struck the world over the last 300 years, the so-called
Spanish flu strain began as an avian influenza virus, mutated into a form that passed between humans, infected a fifth of the world's population, and killed up to 50 million people, including more than 650,000 in the United States.

Today, it is avian flu H5N1 the most virulent subtype of the influenza A type viruses, that has set the world on edge. (Influenza viruses are classified as A, B or C types, though in recent years, only the subtypes of influenza—particularly H1N1, H1N2 and H3N2—have been circulating in human populations, causing seasonal flu outbreaks. All pandemic-causing viruses have also been type A and some suggest that H5N1 resembles 1918's deadly strain.)

Since its initial 1997 outbreak among poultry and humans in Hong Kong, this highly infectious virus has spread from Southeast Asia into Europe, Africa, and the Middle East. As of this writing, scientists and media are turning their focus to Alaska, where avian flu is expected to make its first North American stop within weeks, brought ashore by migratory water birds returning from their winter stay in Asia. By many predictions, it will hit the West Coast by autumn.

Mapping mutations

While hundreds of millions of birds, primarily chickens, have died from the disease or mass exterminations of exposed flocks—with losses in the billions for poultry industries in affected countries—H5N1 is far from reaching pandemic status among human populations. Scientists are quick to remind the public that although H5N1 is clearly a dangerously lethal virus, it is first and foremost an avian disease. To date, birds—not people—are its predominant "hosts" and victims. So far, there are still no corroborated cases of human-to-human (or "H2H" in bird-flu parlance) transmission. The people who've contracted the virus and died from it have been predominantly poultry farmers or workers in live bird markets who had extremely close, prolonged contact with infected animals.

Photograph of Eddie Holmes
James Collins

Eddie Holmes

In fact, says Penn State virologist Edward Holmes, though each human death from H5N1 is a tragic loss, the total human death toll is just over 100. "You've got to put it into context," urges Holmes. "Every year, 36,000 people die of normal, seasonal flu. That's a large number of deaths."

British-born and Cambridge-educated, Holmes pads around his offices in University Park (where posters of viral genetics share wall space with an homage to Homer Simpson) looking more like the boy-genius-next-door than an integral member of the university's pioneering Center for Infectious Disease Dynamics. ("Call me Eddie," he says.)

His latest endeavor? "I'm involved in an unofficial capacity with the National Institutes of Health's Influenza Genome Sequencing Project on how human flu evolves from season to season," says Holmes. "We have to decipher the dynamics of 'normal' seasonal human flu and we don't have that completely understood yet," he explains. "There's been a lot of dogma for thirty odd years about how the virus does what it does and it hasn't really been challenged until now."

What the influenza virus does—and does extremely well—is mutate. In particular, RNA viruses such as influenza replicate very quickly, making lots of mutations—essentially, transcription errors—as they go. Not possessing the "repair kit" enzyme polymerase that is present in DNA viruses, they can't correct their replication. "And what happens," says Holmes, "is that a subset of those errors turns out to be beneficial to the virus and allows it to spread more efficiently through populations."

Outsmarting viral evasion

"This NIH study," he enthuses, "is a huge genomics project, sequencing hundreds—thousands!—of flu genomes from around the globe. But the clever thing is that, rather than doing a random sampling from different populations, this is a micro-evolutionary study that analyses the flu's diversity in a single population over several years."

One goal of the NIH study is to better understand how the highly variable flu virus often evades our attempts to immunize against it—an event described in the biomedical community as "vaccine failure." In the seven years of this ongoing study, the intensity of focus and "fine level analysis" have yielded "an absolute gold mine" of information about flu evolution, says Holmes.

"It's far more complicated than we knew," he adds. "What we've shown is that flu viruses can exchange genes—in a process called reassortment or recombination—more than we ever thought they did before. Most of the new variations it creates won't be particularly useful to it, but it's turning over phenomenally quickly—I can calculate the rate of evolution per day in the virus—and what appears to happen is that every few years, the virus makes a bigger jump in evolutionary space than we can predict."

A better understanding of this process, declares Holmes, is "fantastically important" if we hope to protect ourselves against both garden-variety seasonal flu and potential pandemics caused by high-mortality strains such as H5N1. (Compared to the typical one percent annual flu mortality rate, H5N1 appears to be killing up to 55 percent of its human victims and 100 percent of infected domestic poultry. Initial human clinical trial results testing an experimental H5N1 vaccine suggest "limited effectiveness".)

Increasing surveillance speed

If the enemy moves rapidly, so must the surveillance and response protocols. In his small lab, tucked away behind barns and agriculture buildings on the University Park campus, Penn State senior research associate Huaguang Lu is making bold strides to improve the world's ability to spot—and contain—the deadly virus.

Photograph of Huaguang Lu with Chickens in the background
James Collins

Huaguang Lu

Lu, born and raised in a small farming village in China's Liaong Province, looks into your face with full attention when he speaks, gesturing on occasion with large expressive hands. His eyes bespeak the urgency he feels when discussing bird flu. "Whenever we have a positive outbreak, it is critically important to isolate the virus as fast as possible so we can do genotyping and molecular sequencing. We need to compare different outbreaks in the same geographic areas to see how it's changing."

And while Lu regards today's technology as "beautiful and wonderful," expensive, diagnostic equipment and highly trained lab personnel are not always readily available in the developing nations where most bird flu outbreaks have occurred. More crucially, in the week or more it takes a farmer to send a suspicious swab or tissue sample to be analyzed and wait for a result, the virus is rapidly replicating, spreading, and—by natural selection— mutating into a more potent enemy.

"In nature, a 'high path' (highly pathogenic) strain doesn't just appear out of nowhere," explains Lu. "It needs to circulate for months or years as a low path virus first. So far, there are 16 hemagglutinin (H) subtypes of avian flu viruses, from H1 to H16, but H5 and H7 are particularly dangerous because they're the most likely to form a highly effective mutation."

The key, says Lu, is constant monitoring and immediate diagnostic answers, so we can detect the virus and stop it in its tracks. To accomplish that, Lu developed a new type of rapid diagnostic test for bird flu. Very inexpensive to produce, simple to use and interpret, portable ("You can take it right into the field") and—most critically—fast, Lu's test represents an important new weapon in our arsenal against bird flu.

The dot-Elisa test --or, dot-enzyme-linked immunosorbent assay--involves applying a swab of fluid from a bird's nasal passage or flesh-tissue sample to strips of membrane-thin nitrocellulose material mounted on paper. Monoclonal antibodies for avian flu (produced at Penn State) are then applied to the strips, followed by an enzyme conjugate and substrate solution for color development. In the presence of an antigen—a live or dead virus—the strip turns purple, providing a clear, visual diagnosis.

When compared to most commercial immunoassay tests for avian influenza, it's easy to see why this new test has grabbed the world's attention: dot-Elisa costs 50 cents per sample instead of 10 dollars; 100 samples can be processed in one batch instead of 10-20; and dot-Elisa is a rapid same-day test, while conventional virus isolation assays can take up to a week to make a diagnosis of avian influenza. Penn State has filed for a patent on dot-Elisa and hopes to license this technology for commercial use.

Meanwhile, Lu is busy working with organizations such as the Food and Agriculture Organization (FAO) of the United Nations to help train scientists and establish virology labs in Southeast Asia. In addition to traveling recently to Laos and Cambodia, Lu has set up an avian virology training program in coordination with a FAO funded project. To date, the project has brought two Iraqi veterinarians to Penn State for eight weeks of training and hopes to bring more scientists from across the globe to Penn State's Animal Diagnostic Laboratory "Virology surveillance is the most important method to monitor avian flu virus in domestic poultry so as to effectively prevent and control outbreaks," says Lu. "Combined with proper bio-security, this technology can help to reduce the risk of a localized outbreak becoming a dangerous pandemic."

Balancing preparedness and panic

When it comes to bird flu science and public health policy, it's not difficult to find conflicts and mixed messages among the pundits and press releases. For instance, are flu pandemics cyclical events? By now, if you've read even a smattering of the daily articles on the spread of H5N1, you've heard the words "due" and "overdue" to describe the world's vulnerability to a new strain.

Consider the words of David Nabarro, the United Nation's coordinator for avian and human influenza, who said who said in a 2005 interview "An influenza pandemic among humans through human-to-human transmission is a certainty sometime...Over the last 200 years, there have been pandemics at intervals of every 30 to 40 years, on average. And we're about due for one now."

"This is shocking from a senior U.N. person," responds Eddie Holmes. "Unfortunately, he is making a very basic error. There is no mechanistic way that pandemics can be cyclical and to say we are due for one shows a very poor understanding of the subject matter."

Migrating birds against a sunset sky
iStockphoto

Six million migratory birds make the annual flight from Asia to breed in Alaska. Will they bring bird flu to North America in 2006?

Regardless of whether it's predictably cyclical or completely random, public health officials are trying to send a message of pandemic preparedness to the American public, while squelching panic and fear-mongering. That's not an easy tightrope to walk.

In a March 2006 speech, Health and Human Services Secretary Mike
Leavitt
made the sobering statement that "Any community that fails to prepare with the expectation that the federal government will be able to step in and save them at the last moment will be sadly disappointed...Local preparedness is the foundation of preparation for a pandemic."

Evoking Hurricane Katrina, Leavitt has suggested that people need to calmly prepare for a possible flu pandemic as they would for a natural disaster. In case people would be urged to remain confined to their homes to stem the tide of infection, Leavitt recommends a slow and steady stockpiling of extra provisions: "When you go to the store and buy three cans of tuna fish, buy a fourth and put it under the bed," he recently told an audience in San Francisco. "When you go to the store to buy some milk, pick up a box of powdered milk, put it under the bed. When you do that for a period of four to six months, you are going to have a couple of weeks of food. And that's what we're talking about."

Meanwhile—while some Americans prepare Armageddon-ready bunkers and others laugh off the pandemic panic as just another Y2K non-event—U.S. spy satellites are tracking the flights of infected wild bird flocks as they head north to Siberia and Alaska, where they'll soon intermingle with flocks from the North American flyways.

"What we're watching in real time is evolution," said Laurie Garrett, a Pulitzer Prize-winning author and a senior fellow for global health at the Council on Foreign Relations, in an interview this spring with ABC News. "And it's a biological process, and it is, by definition, unpredictable."

Eddie Holmes, mapping flu genomes at his computer under the watchful eye of Homer Simpson, would agree. Despite the explosion of citizen-journalism on bird-flu on the Net (at sites such as Fluwiki and Flickr's Avian Flu Watch), we are all essentially in the dark, watching the movements of birds and wondering what the virus has in store for us.

"The bottom line," says Holmes with an unflappable British delivery, "is that we don't know what will happen and we don't know when it will happen."

What we do know for certain is the power of one word—pandemic—to focus the full attention of an anxious planet.

Google earth's avian flu map

To view the Bird Flu map in Google Earth:

  1. Install Google Earth (free software).
  2. Click here to load the Bird Flu dynamic layer which will automatically install the Bird Flu feed.

Once you've installed the layer, save the feed from your temporary folder to your My Places folder in Google Earth, otherwise you'll have to reload it each time. Once loaded the feed will refresh each time you launch Google Earth, keeping you up to date with Bird Flu news.

Edward Holmes, Ph.D., is professor of biology. He can be reached at ech15@psu.edu.Huaguang Lu, MPVM, is senior research associate in the department of veterinary and biomedical sciences. He can be reached athxl15@psu.edu.

Last Updated June 05, 2006