AVIAN INFLUENZA: (a.k.a. BIRD FLU)

These days, a common topic of conversation in our clinic is the “bird flu.”  Travelers, especially those going to Asia, are asking what they can do to prevent this disease and what they should do if they get it.

Before we can discuss bird flu, however, we have to explain a few things about influenza in general.

The reason so many people get flu every year, and the reason there is an annual vaccine, is that the flu virus is always changing.  The virus has eight genes with an almost infinite variety of small variations.  With the virus constantly reproducing in millions of people, small mutations can occur and then be spread to other people.  Every year, institutions like the Centers for Disease Control and the World Health Organization study the changes in the flu virus.  Then a vaccine is prepared against the most common strains for that year. 

As the flu season is different in the Northern and Southern Hemispheres there tend to be significant differences between the viruses in the two hemispheres.  Thus there is a different flu vaccine produced for each hemisphere every year.

It is the proteins on the surface of the virus that cause disease in humans.  Two surface proteins in particular are responsible.  These are the HA (hemagglutinin) and NA (neuraminidase) proteins. There are 16 varieties of HA proteins and 9 of NA.  The three common influenza A viruses in humans are H1N1, H1N2 and H3N2.  Minor changes in these from year to year are why last year’s flu does not render a person immune this year.  The larger the change, the more severe the illness is likely to be.

The strains of influenza that occur in birds are often only slightly different from those found in humans.  And in many cases, not a great alteration is needed in order for the virus to be able to spread to humans.  In fact, much of the “antigenic shift” that occurs year to year is thought to occur first in birds and then spread to humans.

So what is so different about the bird flu that we are hearing about now?  The difference is in the genetics.

Since 1997, there actually have been at least three varieties of bird flu that have caused illness in humans.  One, however, the H5N1 variety, is the one that’s making the news. 

This virus is so different from human flu viruses that it is surprising that it can spread to humans at all.  People who have gotten this flu have become seriously ill.  And serious illness is not just limited to the frail and elderly.  So far, over 130 people in 7 countries have gotten this type of flu and over half of them have died.  These mostly have been otherwise healthy people. 

What is frightening about this virus is this unusual degree of virulence.  Even among birds, literally millions have sickened and died from it even though flu is a very common disease among birds and they rarely die from it. 

Human cases first occurred in the Far East. Two possible factors for this are that humans and birds live in close proximity to each other in these cultures, and it is not uncommon to eat under- or uncooked bird products.  More recently, human cases have occurred in the Near East.

Bird epidemics were at first occurring primarily in these same countries but cases now have been found also in Africa, Eurasia and Europe. 

There may be some encouragement to be found in the fact that in some bird populations the virus is rampant but the birds are not very sick.  Similarly, the people who are getting seriously ill may be only the “tip of the iceberg.”  Maybe only these are seeking medical care while many more, even though they have the virus, are getting only mildly ill.  This has been much the case with the dreaded West Nile Virus.  There was some evidence from the Near East that this was the case in humans, but so far that data has not been confirmed.  Which means that scientists still suspect that an infection with this virus will almost always cause serious illness.

Two recent developments have scientists worried that this virus is mutating to a form that might be able to spread among humans.  One is that birds that have the disease (ducks in this case) are surviving longer and shedding virus longer than previously, making them more capable of spreading the disease to humans.  The other is that now the virus is starting to show up in other mammals such as pigs and leopards.

So far there have been very few cases of human to human transmission.  When members of the same family come down sick with the same disease, it is difficult to be certain whether they caught the disease from each other or from the same animals.  But one or two cases have been at least strongly suspicious for transmission from one family member to another.

But with the virus now circulating among millions of birds, the risks increase of another small mutation that would allow easy transmission from person to person.  And there is certainly nothing to indicate that it would be anything other than a very serious disease.

If such a mutation were to occur, we could easily have a “pandemic” or a global epidemic.  Since the virus has now been found both in Asia and in Europe, this could start in either of those places and, given modern travel patterns, rapidly spread to anywhere in the world. 

As this virus is no respecter of persons, it would not be just the old or frail who would get ill. Entire populations could become seriously ill, flooding hospitals and other health facilities, shutting down schools and institutions and even making it impossible for normal human services such as transportation to continue—to say nothing of the millions of deaths that could be expected.

To try to prepare for this sort of eventuality, the Centers for Disease Control, World Health Organization and other entities are promulgating plans for prevention and response.  There are preparedness plans available for businesses, local governments, health facilities and transportation systems.  Probably looming most in people’s minds is the hope of a preventive vaccine.

Health authorities are more than ever urging people to get the normal, annual flu vaccination.  It is unlikely that this will be very protective against the “pandemic flu” should it occur, but it would protect against the common flu, thus preventing the added burden of that disease as well as the confusion that occurs when two diseases have similar symptoms.

A candidate “bird flu” vaccine is under trials, but there are several factors preventing mass production.  One is the fact that until the true “pandemic” flu virus emerges, it is impossible to produce a vaccine that precisely fits it.  Remember that ANY flu virus can mutate, so we could produce millions and millions of doses of vaccine against the current H5N1 virus only to discover too late that this is not the virus that is causing the pandemic.

Another problem is that the usual method of producing flu vaccine is to slightly weaken the virus and then inoculate it into millions of chicken eggs to reproduce.  But since the H5N1 virus is a BIRD flu, the virus kills the very eggs into which it is inoculated and thus no further vaccine is produced. 

New methods need to be found to produce huge quantities of the vaccine.  Current production methods are very labor intensive.  Someone, for instance, has to physically, one by one, inoculate thousands of eggs—perhaps duck eggs in this case.  Other, more mechanized methods are under investigation but it is anyone’s guess whether this can be accomplished before a major outbreak occurs.

So what can we do for now?

Current recommendations are that if you are traveling to a country where the bird flu has occurred, you avoid close contact with birds, bird droppings, feathers and other bird products.  And you avoid eating any bird products that have not been thoroughly cooked.

The most effective, most common and most overlooked means of protection is, as always, to WASH YOUR HANDS.  Even though droplet spread probably does occur through sneezing, etc., most of these germs are spread by getting them on your hands and then touching a mucus membrane such as your eyes, nose or mouth.  Vigilance in this area is your BEST method of self-protection.

Debate rages as to what should be the role of antiviral medications.  Two of the currently available anti-flu medicines, amantadine (Symmetrel®) and acyclovir (Zovirax®), already have been shown to be ineffective against the H5N1 virus.  That leaves oseltamivir (Tamiflu®) and zanamivir (Relenza®) as the only choices left.

These medicines could not be counted on to prevent the spread of the disease.  They merely reduce the severity and duration of the infection once a person already has it.  A person could be spreading the virus for several days before they themselves became sick.  But taking these medicines might help to keep some people out of the hospital.  Early evidence, however, is that the H5N1 virus is at least partially resistant to Tamiflu.  In the cases where it has been used, higher doses than usual and longer exposure have been required in order for it to make a difference.

Experts are also advising against stockpiling these medicines.  Firstly, because there is still no evidence that they will work.  Second, because all of these medicines have some side effects and more people might actually die from the side effects than would be saved by the medicine.  Third, by the time any outbreak occurred, the stored medication might be outdated.  And finally, small amounts of medicine stockpiled in multiple locations might prevent there being enough medication for the ONE location where it was needed.

Some companies that are doing business in the affected areas of the world, however, are keeping a small supply of these medications to be given to any of their employees who might come down with flu-like symptoms.  For the reasons given above, we would not advise their being given prophylactically.