The cryoelectron tomography
photo (above) offers an actual
look at the eight segments of
RNA (each segment is circled in red)
that carry the genetic information
coding for the influenza virus. The
spikes around the edge of the virus
are the hemagglutin (H) and neur-
aminidase (N) glycoproteins.
(Photo courtesy Harris A., et al, PNAS,
2006, 103, 19123-19127 © 2006, USA,
all rights reserved.)

Alice Huang talks about avian flu and the influenza virus

If “whatever happened to avian flu?” has been a frequent refrain in recent weeks, that only goes to show that Nature’s attention span is a lot longer than the general public’s. The intermittently overwrought news coverage that raised the flu strain known as H5N1 to the status of “fear factor of the month” in 2006 may have subsided, but the threat that this deadly virus, in particular, and the potent mutability of influenza, in general, poses to human populations remains very real. Bird flu’s transmission among both wild and domesticated birds throughout Asia and Europe continues to be closely monitored, and national and international health organizations are keeping a vigilant eye on scattered new human cases (recently reported in both Southeast Asia and North Africa), amid ongoing concerns that the virus might mutate into a form that would allow it to be easily transmitted among humans.

Caltech News asked faculty associate in biology Alice Huang, Caltech’s first lady from 1997 to 2006 and internationally known for her research in virology, to talk about the origin and spread of H5N1, the history and biology of the influenza virus, and the public-health and biomedical implications of the emergence of new strains of flu. For more than two decades, Huang has consulted widely on science policy for the United States government, as well as for the governments of Taiwan, Singapore, and China. Much of this work has dealt with issues related to the nature, treatment, and prevention of infectious viral diseases, including five years as a member of the Vaccines and Related Biological Products Advisory Committee, which advises the Food and Drug Administration on the safety, design, and production of various vaccinations for influenza and other diseases. From 2003 to 2005, she served as chair of the International Science Panel on SARS (Severe Acute Respiratory Syndrome) for Singapore’s Agency of Science, Technology, and Research.

Huang was interviewed by Heidi Aspaturian, the editor of Caltech News.

Can you explain first what H5N1 means? Is the anxiety we’ve seen in recent years over this particular strain of avian flu justified?

H refers to hemagglutin, the substance that enables an influenza virus to bind to and infect a specific type of cell, and in the case of H5, the substance is specific to bird cells. N, for neuraminidase, is another surface substance that allows new copies of the virus to escape infected cells and migrate to uninfected cells. We’ve known for some years that H5N1 evolved in a bird host. However, when you consider the extent of crossover that has already taken place in China, Vietnam, and other Asian countries, it’s pretty clear that this strain is one that can move into humans. And that immediately brings to mind the great flu pandemic of 1918, which also involved a deadly new strain of avian flu that not only got into people, but also evolved into a form that was easily transmissible from person to person. The estimates of how many people it killed have recently been revised upward to some 40 million. Knowing that, and knowing the nature and history of the influenza virus, you have to be concerned that this could happen again. We now know that the H5N1 strain has been rearing its ugly head in Hong Kong since 1997. Millions of chickens have been culled—that is, slaughtered—since then in an effort to prevent further spread. Yet the crossovers into humans have continued, and overall the number of crossovers has risen from one year to the next. So, that is certainly cause for concern.

There seem to be two schools of thought about when, if ever, this strain of flu will reach the United States. One view holds that its arrival is inevitable. The other maintains that it’s unlikely to show up any time soon, if at all. Where do you fall along this spectrum?

Based on what I’ve read and seen, you could argue either way. I visited Fujian province in southeastern China last spring. Seeing how the people lived in proximity to animals in some of the local villages, I realized how unlikely it is that we are going to have that same type of close contact with birds in the United States. We may indeed see infected birds here, but it doesn’t mean that bird flu is going to spread here—or in other developed countries—in the way that it has in parts of Asia. If and when it arrives, it’s possible to take some simple and quite effective precautions: don’t handle dead birds without gloves, don’t pluck their feathers, don’t play with them, and don’t use them as footballs. Because this is actually what I saw in parts of Fujian, and it’s a type of behavior that is fairly common throughout parts of Asia.

During a trip last year to southern China, Caltech virologist and faculty associate in biology Alice Huang took these pictures (left and right) of unique roundhouse dwellings whose busy communal courtyards create ample opportunities for bird and human (note child in well at right) repositories of different flu strains to all mingle together.

I went to the Chinese countryside in part to look at some interesting populations that traditionally have built and lived in very large, round communal houses, some of which can house up to ten families. Each of these dwellings has a central courtyard, and nearly all of their food preparation, washing, and recreation takes place there. You see ducks and chickens there, with wild birds flying in and out, and puppies playing with the chickens and chasing them. In one of these courtyards, I watched a woman cleaning a chicken that she had recently killed. She poured buckets of water over the fresh carcass, and then the puppy came and drank the water, and then the children raced around playing with the puppy. The kids will also collect the big feathers from these freshly killed birds to make a kind of shuttlecock that’s weighted down with Chinese coins and tossed back and forth as part of a game. So you can see what kind of interspecies interaction is going on. It’s hard to imagine that we would find ourselves in this type of situation in the United States, but it’s precisely the sort of behavior that creates the potential for diseases like influenza to spread from wild birds into domesticated animals and into humans.

Is China’s government making any effort to educate the population, which has obviously lived this way for centuries, about the risks inherent in this way of life?

They’re not mounting a public campaign, with billboards and so forth, as they’ve done with AIDS. They are working more closely than in the past with the World Health Organization (WHO), which has been keeping a close eye on what’s going on. Among other countries in the region, Thailand has maintained excellent veterinary surveillance over birds and other possible animal reservoirs, and Vietnam is starting to take some steps to deal with what the government now recognizes is a problem. But many other nations in that part of the world—Indonesia, in particular—really have no veterinary services. They’re lucky if they have even any coordinated sort of human health surveillance. This is a serious issue in many underdeveloped countries in Asia, and it’s probably even worse in Africa.

So, let’s look at the United States. You have been quoted more than once as saying that our government is not doing nearly enough to deal with the perils posed by this strain of influenza and other possibly deadly future strains.

Until very recently, that has definitely been the case. The key turning point may have been at a 2003 National Academies Institute of Medicine research meeting that focused on the outbreak of the SARS virus that year in Hong Kong and elsewhere. A scientist at the meeting pointed out that historically the flu has posed a much greater threat to humans than SARS. Individual scientists had been worrying since 1997, when these ominous new avian flu strains appeared in Hong Kong, but I think that this meeting marked the beginning of a consensus that more needed to be done to monitor the continued progression of transmission between birds and humans.

In the government sector, a lot of this work has been centered in the Vaccine Research Center, which the Clinton Administration set up within the National Institutes of Health in 1999 to facilitate the development of an HIV vaccine. In the last six years, it has also mounted vaccine trials for West Nile virus and Ebola, and has tested the first effective vaccine against SARS. In 2004, it received one of the first government contracts to develop a vaccine against H5N1, and just this past fall, it reported that it had developed a vaccine that apparently protects mice against that deadly 1918 strain of Spanish Influenza. These are very promising developments, and now the private pharmaceutical companies have also become interested in pursuing research along similar lines. They have finally started getting support from the federal government to ramp up their activities.

What kind of bird-to-human influenza crossovers have we seen since the deadly outbreak in 1918?

In 1957 and 1980, we had two relatively minor pandemics, which also seem to have originated with birds in East Asia, but they didn’t come close to what happened in 1918. In large part I think that is because in recent decades, scientists have learned a lot about the influenza virus and its ability to mutate into new forms. A small but active group of scientists has been monitoring this aspect of the virus since the 1960s, and their vigilance has been largely responsible for the kind of response we saw in 1997, when the H5N1strain first surfaced in Hong Kong. These specialists flew out there and assessed what was happening. They recommended culling the chickens, and it was done.

Is this group part of the WHO?

They have close ties with it, but they work out of St. Jude’s Children’s Research Hospital in Memphis, Tennessee. The leader is a scientist named Rob Webster. For decades he has been at the forefront of this research, and he has gone all over the world, capturing migrating birds and testing them for avian flu. He was one of the first to point out that because of the mutability of the influenza virus, humans are always at risk of being exposed to a deadly new strain.

The scenario the world is dreading: A human cell is infected by human and avian influenza at the same time, and the two strains recombine to deadly effect. In the above artist’s rendering, the H5N1 avian flu virus with the eight dark blue RNA segments (at the right) and the human flu virus with eight orange RNA segments (middle) simultaneously enter the cell and spill out their contents, which travel into the nucleus (lower right), where they replicate. New copies of the viral RNA, represented by the thin blue and orange chains at lower left, stream back out into the cell and gather below the cell’s outer membrane, where they assemble into new virus particles that bud out from the cell. During this assembly process, the segments from the avian flu strain (dark blue) may mix with segments from the human flu strain (orange) to produce new viruses that combine genetic elements from both strains (note the two orange segments that have joined the six blue in the virus particles at drawing’s left). A combination of these different genomes that is fatal to humans as well as to birds and easily contagious among humans could give rise to a deadly pandemic. (Illustration © Russell Kightley Media, www.rkm.com.au.)

What is it about influenza that makes it so prone to mutation?

Let’s do a quick primer on the influenza virus. Most organisms have their genetic material encoded in the DNA molecule, but viruses, depending on what type they are, can encode theirs in either DNA or RNA. Now RNA is more prone than DNA to making coding errors during replication. This makes perfect sense once you realize that RNA, unlike DNA, doesn’t consist of a double polymer strand—the renowned double helix—but only a single strand. So an RNA-based virus like influenza lacks DNA’s self-correcting mechanism for errors and produces many more of them during a replication cycle. Most of these mistakes are lethal and simply self-destruct, but every once in a while, you get a mutation that confers an adaptive advantage and begins to successfully compete with and eventually outstrip forms of the virus that lack the mutation. So while most of the RNA mutations go nowhere, their relative number is sufficiently large that you end up with many more successful ones than you would have in a DNA-based virus.

Although most avian influenza cannot attach to human cells, the current H5N1 strain has already mutated enough so that it can infect humans. It has also become more lethal to both birds and humans. However, it does not pass from human to human very easily.

Influenza also has a striking oddity about it. Most RNA viruses consist of a single, very long polymer strand. The influenza virus is made up of eight such strands, of varying size, each of which is totally separate from the others. If two different influenza viruses infect a single host and find themselves growing together in the same cells, the potential is there for the eight individual strands to reshuffle and reassemble themselves. What this means from an evolutionary standpoint is that it’s much easier to introduce new genetic material into this type of virus. Besides the strands that code for H and N, there must be a strand or strands that code for the ability to pass easily from human to human. Should this property be reshuffled into the current H5N1 avian strain, the virus would gain the ability to pass easily from one human to another. So now you’ve got a new avian flu variant that can not only slip through the human immune system response but also spread readily in a human population. We know that this type of crossover occurs commonly for pairs of viruses grown in the same cells in the laboratory, in addition to the many small mutations.

The thinking had been that the 1918 flu arose from such reshuffling, but recent sequencing studies suggest that the virus may be mostly avian and that numerous small mutations gave it the ability to infect humans and spread readily.

Is there any sense of how many steps in a mutation sequence would be needed to create this type of lethal strain?

It is possible that just one mutation could do it—if it’s the right mutation. What we’ve been looking for since the Hong Kong outbreak in 1997 are indications that H5N1 has picked up any of the RNA segments that we recognize as being in the run-of-the-mill human flu. So far, we haven’t seen much evidence of it. We have seen mutations, and there have been a handful of well-documented cases of person-to-person transmission. But each of those, so far, turns out to have been a special case.

Differing and evolving responses to the bird flu threat in Asia can be traced through this series of United National Food and Agricultural Association (FAO) photographs. At upper left, the carcasses of chickens that have either died from the disease or been slaughtered to prevent its spread are burned in Vietnam; upper right, an Indonesian chicken becomes one of 115 million in that country to receive an avian flu shot in 2004. At lower left, a net is installed at a duck farm in Thailand to protect the ducks from contact with wild birds.

Overall, how common is it for diseases to migrate from animals to humans?

It happens quite often. HIV is one outstanding example that we have now documented pretty well. SARS clearly has a reservoir in another species somewhere, although there’s not a consensus about which one it is. The Ebola and Marburg viruses are two more examples of extremely lethal germs that have made this animal-to-human transition. We hear and talk a lot today about political terrorism, but as the director of the NIAID [National Institute of Allergy and Infectious Diseases] has put it, nature’s terrorism is occurring all the time. We also have to be aware that indiscriminately slaughtering animals is not an effective means of prevention. Targeted killing of livestock may sometimes be necessary, as we have seen with chickens in the Far East, and in some parts of the world, they’re starting to vaccinate poultry as a humane alternative. Right now the focus has turned to wild birds that harbor the avian flu virus, and obviously you can’t catch and kill them all.

What would you consider to be the best course of action?

Our best defense against nature’s terrorism is good surveillance, sound understanding of the diseases, plenty of preparation in terms of vaccine production, and making sure to take advantage of the vaccines that already exist. Obviously there are some things only the government can do, and adequately funded R&D is one of them, but there are other effective and elementary precautions we can take in our everyday lives, such as barrier protection. In certain cases, this could even include face masks, if they’re used properly, but it also means avoiding large gatherings and staying home from work if you are ill. American workplaces really need to think about actively enforcing their sick-leave policies. They aren’t doing themselves any favors by encouraging unwell employees to come to work and spread communicable infections around. The WHO has repeatedly advocated frequent and thorough hand washing as one of the most effective ways to reduce the spread of contagious diseases. Here in the West, we tend to shake hands and hug and kiss a great deal. I don’t think that we would be happy behaving like the Japanese, who traditionally bow to one another as a form of greeting, but the WHO has actually suggested that we bump elbows rather than shake hands. That gives you some touching, and you can make the contact stronger or weaker depending on how you like it to be. So, you have these really quite useful low-tech strategies, along with the very sophisticated techniques being developed and tested in the laboratories. Clearly, the science is there. The technology is there. Not to take advantage of it is foolish. The best way to deal with a potential public health crisis of this magnitude is to stop it before it starts.