Sunday, March 06, 2005

Public Confusion Surrounding Influenza

“I am sorry I missed class last week, but I had the flu,” said one of my students. My eyes narrowed as I looked more closely at her face.

“The flu, huh?” I said skeptically.

“Yes, but it wasn’t that bad; I got over it in two days.”

“Two days? Are you sure you had the flu?”

“Well,” she paused. “It was the stomach flu.”

She didn’t look like a flu survivor, but I tried to keep my annoyance to myself. Confusing a transient bacterial infection with influenza is a pet peeve of mine, especially since health officials around the world are trying to stop an epidemic of one particular strain of avian influenza.

Apparently, the misunderstanding about flu is traditional and widespread, even among those people who have the easiest and best access to information about these things, such as my pre-nursing students. (“Influenza” is Italian for “influence”, from the Latin, influentia because it was thought to be caused by a bad influence from the heavens). In fact, the vague phrase, the “stomach flu”, is over-used to describe several symptoms that are often mistakenly attributed to influenza; nausea, vomiting or diarrhea. In reality, these symptoms rarely result from influenza but instead, are caused by a variety of microbes, including parasites, bacteria and other viruses. Thus, it is my opinion that using the “flu” or “stomach flu” to describe these symptoms leads the public to underestimate the real danger from influenza, especially now that a potent strain of avian influenza looms on the horizon, threatening to become a pandemic.

Even though these pandemics are largely forgotten, influenza is a proven killer: during the 1918 pandemic of “Spanish flu”, more than 20 million people died worldwide in only one year, including more than 500,000 Americans – in fact, more people died from the 1918 flu than died during the four year reign of terror during the dark ages caused by the infamous “Plague”, or “Black Death” (“Plague” is caused by the bacteria, Yesinia pestis). Even during non-pandemic years, influenza causes more than 200,000 hospitalizations and 36,000 deaths each year in the USA alone.

In contrast to the other microbes, the bacteria and protozoans, viruses are tiny; they are often thousands to hundreds of thousands of times smaller than these other infectious organisms. In fact, viruses are the smallest units of life, although many scientists, including myself, do not think viruses are truly alive because, unlike other microbes, viruses do not possess essential biological machinery so they must invade living cells and force them to carry out all functions necessary to replicate themselves.

Similar to most microbes, influenza tends to cause disease in the very young and the very old – those with immune systems that are somehow compromised. Symptoms of influenza include rapid onset (within hours) of acute upper respiratory disease accompanied by high fever (typically 101-105), myalgia (muscle pain), headache, fatigue and pharyngitis (sore throat). Additionally, the patient may have a cough and in severe cases, prostration. Coryza (runny nose) is unusual for influenza (runny nose characterizes common cold infections, more than half of which are caused by another group of viruses, the Rhinoviruses). Additionally, influenza selectively preys upon those with chronic cardiopulmonary diseases, making their chronic health problems worse. For example, people with asthma may experience severe asthma attacks and people with chronic congestive heart failure may experience worsening of this condition while they suffer from the flu.

Not only is infection with influenza potentially deadly by itself, but it also weakens the host, creating opportunities for other microbes to invade and cause disease. Microbes, such as Adenoviruses, as well as a variety of commonly occurring bacterial opportunists, especially Haemophilus influenzae, Staphylococcus aureus, and Streptococcus pneumoniae, often cause secondary infections of pneumonia, bronchitis or serious ear infections. But in contrast with influenza, which responds only to treatment shortly after initial infection with expensive anti-viral medications, secondary bacterial infections often do respond to treatment with antibiotics.

The incubation period for influenza is very short; 1-4 days (“incubation” is the period of time that elapses between initial infection and when the first symptoms develop). Adults typically can pass the virus to others for three to seven days after symptoms begin while children are usually infectious for longer than seven days. Additionally, an infected person can transmit the flu to others starting one day before he or she feels sick. Further, some persons can be infected with the flu virus but show no symptoms at all. But even though they are asymptomatic, they can still spread the virus to others.

Influenza is primarily an airborne disease and thus, spreads rapidly when coughs or sneezes produce airborne respiratory droplets containing the virus particles. When these droplets are inhaled into the pharynx or the respiratory tract, a new host can become infected. The combination of its short incubation time and its airborne transmission allows influenza to spread easily and quickly. Because an individual can fly halfway across the world in less than 10 hours, it is possible for one person to transmit influenza to hundreds of people who are thousands of miles apart, potentially triggering a pandemic.

Influenza is classified as a member of the viral family, Orthomyxoviridae, due to similarities in the structure of its outer protein coat (the outer protein coat gives the virus its “fuzzy” appearance, as seen in the accompanying electron micrograph) and shared genomic features. Influenza’s hereditary material is unusual, consisting of eight distinct pieces of ribonucleic acids (RNA) rather than the more familiar deoxyribonucleic acids (DNA) that are typical for most organisms, including humans and birds.

There are three types of influenza (types A, B, and C) but Influenza type A is most virulent and worse, it can infect humans and many domestic animals, including pigs, horses, chickens and ducks, as well as wild waterfowl. This ability to infect several different species is rare for viruses and significantly adds to influenza's deadliness. For example, when several different animal species’ influenza viruses infect the same animal host, each individual virus particle can increase its virulence by swapping pieces of its genetic material with those from influenza viruses that specifically infect other animal species. When this happens, the resulting new virus has undergone “genetic reassortment”. Because avian influenza viruses cannot cross the “species barrier” to infect humans (and vice versa), birds and humans have historically been protected from direct infection by each other’s flu viruses. However, since most avian and human influenza viruses can readily infect pigs, they undergo genetic reassortment there, and thus, the resulting “mixed viruses” are frequently referred to as “swine flu”. Because human, avian and porcine immune systems have never before seen these resulting “mixed viruses”, its victims are slow to develop an effective immune response and the resulting “swine flu” can thus be quite lethal.

The current form of avian influenza in Asia is unique: this virus surprised health officials by developing a limited ability to cross the “species barrier” between birds and humans without relying on pigs as intermediaries and without first undergoing a genetic reassortment. In fact, until 1997, avian influenza had never been known to directly infect humans, but in that year an outbreak of Avian Influenza type A subtype H5N1 infected 18 people in Hong Kong, killing six of them. But fortunately, this virus could not spread easily between humans, so it did not result in a pandemic. Similarly, another outbreak of H5N1 Avian Influenza in humans in late 2003 and early 2004 did not cause a pandemic mainly because it also could not spread easily from person to person.

But avian influenza’s inefficient cross-infectivity to humans may not last forever, especially in a virus such as type A influenza, which specializes in undergoing large genomic rearrangements that result in abrupt alterations in transmissibility, infectivity and virulence.


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Source material:

Electron micrograph of an influenza virus.

Avian influenza (bird flu) by the Mayo Clinic Staff.

My brain, which collects all sorts of information from the many (many!) papers, books and magazines that I read, from the scientists who tell me cool things, and from the superb university classes I've taken.


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More Essays about Avian Influenza;

Avian Influenza and 'The War on Birds', Part 2.

Avian Influenza and 'The War on Birds'.

Influenza: How Its Biology Affects Vaccine Production.

Public Confusion Surrounding Influenza.

Is Avian Influenza THAT deadly?


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This essay was recognized as among the "Best Medical Blog Writing" by
Medical Grand Rounds XXV.

The Tangled Bank

Included with "The Best of Science, Nature and Medical Blog Writing"
Issue 24.

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© 2004, 2005, 2006 by GrrlScientist

10 Peer Reviews:

Blogger Joe said...

Since you've brought it up, and I've always been curious... if a virus is not, technically, alive, what is it? Essentially a toxin or something?

11:03 AM  
Blogger Peruby said...

I'll definitely think twice before I ever say "I have (or had) the flu" again. Wow! I have read about the pandemic and swine flu's, but certainly have not had it explained in such understandable detail. Great job!

1:56 PM  
Blogger BotanicalGirl said...

joe: As a biologist myself, I would classify a virus as 'infectious hereditary material' or something like similar. Basically viruses are just DNA or RNA inside a molecular injector that allows the DNA/RNA to get inside the cell.

Very nice post, Hedwig. I haven't brushed up on my flu knowledge in a while.

3:44 PM  
Blogger GrrlScientist said...

Hi Joe, basically, BotanicalGirl got it right in her description. Basically, a virus is comprised of proteins wrapped around DNA/RNA. The virus takes over a cell and causes all of its "machinery" to make more replicas of the virus particle using the genomic information that was injected into the hapless cell. Most viruses are very specific as to what sort of cell (and species!) they attack .. an avian neuron or a human mucosal cell, etc. One day very soon, scientists will learn how to efficiently extract harmful viral DNA/RNA from a virus protein capsule and replace it with "helpful DNA/RNA" that will allow us to use them as a targeted molecular gene surgery package for gene replacement therapy.

Thanks for reading, peruby! I'm glad you enjoyed it. It's been awhile since I've seen you here!

6:46 PM  
Blogger Joe said...

So a virus is something between a biological "monkey wrench" and a covert agent? (While a bacterial infection really is more like an invading army? Pardon the English major; I can only think in analogies and images...)

Amusing parallel... in computing, I get frustrated dealing with people who think they have a "virus" when what they really have is self-inflicted "spyware". And while there are categories of computer viruses which act a lot like natural viruses (taking over the host for self-replication), for some reason we call those viruses "worms."

More fun from the folks who make you click "Start" in order to stop...

10:45 AM  
Blogger GrrlScientist said...

Joe: well, we both are learning new things. I could never figure out what a computer worm really was because it sure didn't behave like a real (parasitic) worm when it got hold of a computer.

On the other hand, your analogy of a virus sounds basically correct. And yes, a bacterial infection is sort of like an invading army .. we can even determine the number of bacterial organisms necessary to cause infection in 50% of animals infected! (of course, one can also identify this number for viruses, too). But unlike viruses, pathogenic bacteria are less selective about who they infect .. almost any warm body will do, in fact.

5:33 PM  
Blogger Marti said...

Well, is it worthwhile to have a flu shot? My 15-month old got the flu from me, despite two shots (in November). Admittedly, I got it much worse. But perhaps that was a fluke.

5:12 PM  
Blogger GrrlScientist said...

I think that a flu shot is worth it, marti .. why not? (for more details on flu and vaccines, read this).

6:39 PM  
Blogger Wolf said...

Yesterday, I felt mostly ok until 6.30PM when suddenly I felt painful, hot, dizzy and I got the strong urge to go to bed. I had a fever (pretty high, 39 degC) all night, severe pain in back, shoulders, legs and arms and hallucinations well into the later morning. After taking aspirin and anti-vomit drugs, I felt better and was able to doze off in between. Today the symptoms are only half bad, but I feel extremely weak, exhausted, drained, and tired. There was no rhinitis, there was no cough and there was no diarrhea - no real other symptoms at all. The doctor I consulted said it was most likely one of those summer influenzas. And it is not over yet - I am still feverish and exhausted, but much better than yesterday. OTC drugs, bedrest and enough to drink are definitely essential. Just in case you were interested :-)

2:18 PM  
Blogger debra said...

Now WOLF has the flu!!

I've been careful to distinguish between flu and "bug" or "virus" since I was laid up for 6 weeks with flu back in... about 1990.

Fabulous article. I understood your explanations, and I am not a scientist.

10:37 AM  

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