January 2006 | Back to Table of Contents

Avian Flu

Avian Flu is Coming!

The appropriate response to recent reports about avian flu and talk of a pandemic is neither hysteria nor apathy. It is, rather, acknowledgement of the threat coupled with appropriate emergency preparedness.

By Harry Hull, M.D.

The warnings are apocalyptic—the messages from the media alarming, but confused. Some of your patients may be fearful; others may not care.

The fact is, no one in Minnesota is dying of avian flu right now, and it’s possible that the avian strain circulating in Asia will never cause a pandemic. But that doesn’t mean we can ignore this issue.

As a physician, what should you be doing to help your patients cope with their concerns about avian flu? What should you be doing to prepare for pandemic influenza? What is government doing to prepare for a pandemic? A closer look at the issues can help you separate the facts from the hype, and better serve your patients’ needs.

The Nature of the Virus
Understanding the influenza virus is the first step in understanding the threat posed by avian flu.

Influenza viruses affect humans, but they also affect many other animals, including horses, dogs, pigs, and, of course, birds. Although influenza viruses generally infect a specific type of host animal, some can infect more than one species.

There are three types of influenza virus: Types A and B are associated with the most serious cases of human disease. Type C viruses cause mild disease in humans. Type A viruses are subtyped using 2 surface proteins—hemagglutinin and neuraminidase. The current avian influenza virus is a type A, H5N1 virus. The human viruses currently circulating—and causing routine “seasonal” influenza—are type A, H3N2; type A, H1N1; and a type B.

Influenza viruses change constantly. Almost every year, mutations produce new strains within a constant type and subtype. This is known as antigenic drift, which occurs with types A and B. However, several times a century, a new subtype emerges in which the configuration of the surface proteins of the virus has been altered. If that happens, for example, a type A, H2N2 strain might emerge. This process is known as antigenic shift and occurs with type A viruses. When an antigenic shift occurs, our immune systems no longer recognize the virus, resulting in more serious infections than would occur with a drifted virus. In the case of an antigenic shift, the virus could spread rapidly around the world. A shifted virus would produce increased rates of infection with consequent increases in hospitalizations and deaths. Three pandemics have occurred during the 20th century—the 1918 Spanish flu (H1N1), the 1957 Asian flu (H2N2), and the 1968 Hong Kong flu (H3N2).

The Connection with Birds
The current avian influenza virus in Asia is certainly a concern for poultry producers worldwide. But why is this virus regarded as a pandemic threat to humans? There are a number of reasons.

First of all, genetic analysis of viruses from prior pandemics indicates that those viruses were derived from avian viruses.

Second, the current avian virus is highly pathogenic. Most avian influenza viruses are of low pathogenicity. They cause no disease—or only mild disease—in birds, and they do not infect humans. Viruses that are of low pathogenicity are common—multiple outbreaks have occurred in Minnesota—and are usually controlled by destroying the affected flock.

The third reason is the difficulty controlling the current virus. The first outbreak of H5N1 avian influenza occurred in Hong Kong in 1997. Although early outbreaks were controlled by killing millions of birds in the surrounding area, current efforts to control the virus through culling have met with limited success. The virus has spread rapidly through Asia, and migrating waterfowl are now spreading it to Europe and possibly Africa. (In Minnesota, most—but not all—poultry is raised in buildings designed to reduce contact with wild birds that may carry avian flu viruses.) Millions of birds have died in Asia from infection with the H5N1 strain of influenza in addition to those that were culled as part of efforts to control it. The persistence of the virus, and the expanding number of infected birds, increase the likelihood of spread to humans.

The final reason for concern is the ability of the virus to infect humans. So far, about 120 people have been infected, and about half of those have died. However, the virus remains a bird virus—its ability to infect humans is limited. To cause a pandemic, the virus would have to mutate significantly so that it spreads easily from person to person. At this point, most human infections have resulted from direct contact with infected birds or their droppings. A mutation in the virus could cause that to change. That might happen in two ways—either slowly, through a gradual adaptation of the virus to humans, or quickly, through recombination with a human influenza virus. When the right mutation occurs, the virus could begin to spread rapidly through the human population.

Preparing for a Pandemic
Influenza is a highly infectious virus that spreads primarily by inhaling aerosolized respiratory secretions and by indirect contact through contaminated hands. During our annual “seasonal” influenza outbreak, large numbers of people are infected over a 4- to 8-week period.

The Spanish flu caused a global pandemic over a 6-month period during a time when people traveled by boat and train. Today, unprecedented numbers of people are traveling by air, which could spread a new pandemic strain around the world even more rapidly. SARS, which is much less infectious than influenza, reached every continent within a few weeks.

How bad would a pandemic be? The worst-case scenario would be a repetition of the 1918-19 outbreaks. The Spanish flu may have killed as many as 100 million people, many times the number that were killed in World War I. In the United States, 25 million became ill and 600,000 died. Influenza normally kills the old, the chronically ill, and—in some cases—infants. The Spanish flu did that too, but it had a particular affinity for people in their 20s and 30s, significantly increasing mortality for that age group. The virus spread across the country in one month, with the vast
majority of deaths occurring in October. A similar outbreak, if it occurred right now, might cause 2 million deaths in the United States. The Health Department projects that 1.25 million people could be ill in Minnesota, with 50,000 people hospitalized and 20,000 deaths—all in a 4- to 6-week period.

But wouldn’t antibiotics, respirators, and intensive care units mitigate the effects of the outbreak? Probably not. Many people died in 1918 within a day of becoming ill. Preserved pathologic specimens from this outbreak are consistent with Adult Respiratory Distress Syndrome (ARDS), not bacterial superinfection. In a similar outbreak today, antibiotics might not reduce mortality significantly. People can recover from ARDS, but they usually need extended periods of therapy on a respirator. There wouldn’t be enough respirators, respiratory therapists, or critical care nurses to provide that kind of care for 20,000 people. With every bit of excess capacity squeezed out of the health care system, there wouldn’t be enough hospital beds for 50,000 people on top of the normal patient load from automobile accidents and heart attacks. Minnesota has had a nursing shortage for several years, and that shortage would be exacerbated when hospital staff start to become ill and die from influenza. The situation would become even more dire if hospital workers chose to stay home to care for family members or because they were simply afraid to come to work. With our just-in-time inventory systems, medical supplies of all kinds might be in short supply.

How about using vaccines or antivirals to prevent influenza? A prototype vaccine has been created, but only 2 million doses are available. This vaccine requires two doses, given a month apart, to provide full protection. There is also no guarantee that a vaccine against the current bird flu virus would be effective against the mutated virus that would cause a future pandemic. Current influenza vaccines are produced in eggs and take at least 6 months to produce. U.S. production capacity is also very limited. New production methods and additional capacity will be required to ensure that sufficient vaccine will be available on a timely basis during a pandemic.

Antivirals are also likely to be in short supply if a pandemic occurs. The federal government has stockpiled 3 million treatment courses of the antiviral drug Tamiflu, and the manufacturer is building a new plant and licensing its patent to generic producers. However, current production capacity is very limited and global demand is high. Stockpiles to treat 25 percent of the population will not be available for several years. There are also early signs that the virus might be acquiring resistance to these drugs, so there is no guarantee that they would be effective.

With that grim picture, what should we do? First, take a deep breath and realize that, although most experts believe that a pandemic is inevitable, it might not come for several years, or even several decades. When it does come, it might be more like the milder Asian or Hong Kong flus than the Spanish flu. As for H5N1, it hasn’t reached North America yet, and it may never come here. Even if migrating birds bring it to Minnesota, it may never affect humans, and it may never become a human virus. You can eat chicken and turkey without worrying. Hunters should wear gloves and wash their hands after cleaning game, but they should be doing that anyway to avoid salmonella. Goose droppings in the park are annoying but not dangerous.

Federal, state, and local governments are planning for a possible pandemic, an activity that owes much to our bioterrorism preparedness efforts. Plans are being made to vaccinate or distribute vaccines or antivirals to the entire state within a week, if they are available. Regional hospital networks are exploring how they can share resources. Communities are looking at how they might care for large numbers of ill people, either at home or in an off-site facility such as a gymnasium. The federal government is working with manufacturers to develop new vaccine production methods and expand capacity. Negotiations are also underway to purchase a large stockpile of antivirals. State government is exploring strategies designed to keep society functioning during a pandemic so that basic necessities such as electricity, heat, water, and food would be available. Government planners are preparing for the impact of school closings, restrictions on public gatherings, and the use of “snow days”—when everyone would be asked to stay home for a week or more—should those measures become necessary.

In the short term, we are not facing an imminent pandemic, and you should feel comfortable in reassuring your patients about that fact. However, you can also counsel them to prepare for a pandemic and other potential emergencies by stockpiling food, water, and emergency supplies.

Some patients also may request Tamiflu for a personal stockpile. The Minnesota Department of Health recommends against doing that because available supplies of the drug will be needed to treat seriously ill people during the seasonal flu outbreak that we experience every year.

Finally, one of the most important things physicians can do is to be alert for respiratory illness in patients returning from Asia. Contact the Department of Health immediately at 651/201-5414, if you encounter such a case. We will advise you on how to collect the necessary specimens so the state public health laboratory can help you rule out the possibility of avian influenza. MM

Harry Hull is the Minnesota state epidemiologist.