Swine (Pig) Flu and Avian (Bird/Chicken) Flu

Dr Jamie Love 2009 © (last updated 18 July 2009)

The previous article "Flu" - recombinant genes on the loose! explains the flu - the virus, its genetics, its H and N designations and its immune effect. It acts as good background for what has gone on in this news-worthy area, so you might want to read it first, in order to get the most understanding about the information on this page.
Here, I will teach you the medical angle about avian flu and swine flu; how it causes disease, preventative measures you can take, vaccination programs, drugs and stuff like that. Most importantly, here you will learn about the history of flu epidemics so you can put today's news into perspective.

In 1918 a strain of influenza A now designated H1N1, but at the time called "Spanish flu", killed over 20 million people worldwide. Forty years later, after considerable antigenic drifting and shifting, a new type A had evolved with completely different looking HA and NA. It was called H2N2 and it ran its course killing thousands of people in the USA alone. In 1968 a strain designated H3N2 appeared. It had the same old NA but a slightly new HA (H3) so it was a partial antigenic shift and was milder in its severity. In 1976 the dreaded H1N1 made a brief and frightening comeback on a military base in the USA. Although it was designated the same as the big killer of 1918, this H1N1 was slightly different due to antigenic drift. As a matter of fact, you cannot judge a flu by its "HN code". H1N1, as well as H1N2 and H3N2, are the "seasonal" flus that are commonly circulating but the H1N1 that is so common does not have the same genetic sequences as the "deadly H1N1 flu" of the past.

So, what about the "chicken flu"?

Over the decades, virologists have collected samples of different influenza A viruses and studied them under VERY tight lab containment.
In 1961 a strain designated H5N1 was discovered in some terns (birds) from South Africa. This strain did very little harm to the wild birds it commonly infected, such as waterfowl (like ducks), but was devastating to chickens! It seems that in our domestic breeding programs, we inadvertently selected for strains of poultry that were very susceptible to H5N1. It could destroy flocks, killing almost all the chickens and rapidly spreading to other farms. So, agriculture authorities closely monitor for H5N1. They will close entire farms and destroy all the birds in it in order to stop the spread. They also monitor wild bird populations for H5N1 in order to stop local outbreaks before the local poultry become victims. When H5N1 is detected in a chicken farm or duck pond (for example), authorities will order all chickens to be kept indoors and restrict transport of domestic birds in the area of infection. Free-range chickens are ordered inside or sentenced to death!

Until the 1990's "avian flu" (H5N1) was only a concern to poultry farmers, because it didn't infect people. Or so we thought.

On the 11th of May 1997 a three year old boy in Hong Kong began suffering from severe respiratory distress. As the influenza virus reproduces in the lining of the lungs, the tissues become swollen and inflamed. The lung tissue is slightly damaged but it usually heals in a few weeks and permanent damage is rare. However, it is common for young kids (and old people) to have a slow immune response and in this case the virus was faster than this poor boy's immune system.

On the 15th of May he was hospitalized with the two most serious complications caused by influenza infection; pneumonia and Reye's Syndrome.
Pneumonia is an inflammation of the lungs caused by infection with BACTERIA. Bacteria are normally kept out of the lungs by a healthy immune system and healthy cilia. Cilia are microscopic hairs that cover the outer parts of lung cells and are also found among other types of cells. They sweep away any bacteria, dust or "goo" that settles in the lung. Influenza infections harm the cilia and thus make a person more likely to develop pneumonia. That's exactly what happened to this boy. Staphylococcus aureus are the bacteria most likely to take advantage of damaged lung tissue. This bacteria is commonly found all over the skin and mucous membranes of a healthy human but they don't cause a problem unless they get out of control. Other bacteria may also "dig in" during the lung infection. I don't have any specific information about this boy, so I cannot be specific about the severity or variety of his bacterial infection. However, in a severe case of pneumonia secondary infections may occur due to Hemophilus influenza and Streptococcus pneumonia.
Reye's syndrome is a rare disorder that sometimes occurs when a child is recovering from a viral infection, particularly influenza. It affects mostly the brain and liver. The first symptoms include nausea and vomiting, but this rapidly progresses to more complex behavioral changes such as confusion or delirium. As the liver degenerates the person's metabolism and blood chemistry change for the worse. Most victims of Reye's syndrome die and most of those who don't will spend the rest of their lives dealing with the residual brain damage. Reye's syndrome is a very mysterious disease that only affects children and is often associated with taking aspirin (but not acetaminophen). Naturally, many people turn to aspirin to relive their flu symptoms but you should NEVER give aspirin to a child under 12 that is suffering from flu-like symptoms, unless directed to do so by a doctor after having discussed the risk of Reye's syndrome.

On the 21st of May this boy died from the complications of his flu. (Note: it is often reported that someone has "died of flu" but they usually die from the complications.) Samples from this boy were tested locally and found to be "an atypical influenza A virus". These were sent to several specialist labs around the world, who reported in August that they had isolated H5N1, avian flu, from the samples. This was the first time this strain had been found in a human! It wasn't until late November, when more cases turned up, that it made the news.

Is "avian flu" likely to become a pandemic?

Probably not. (Notice I said "probably"). A pandemic would result only if the avian flu could pass from one human to another. Although the results (so far and to my knowledge) cannot rule out that possibility, there is certainly no evidence that H5N1 can pass from human to human and I would expect to have seen some evidence of that by now. My opinion is based upon the results of a few lab tests reported by the Center for Disease Control (the experts) on December 27th, 1997. Further data may change my mind, but so far I'm not worried and here's why.

All strains of influenza produce strain-specific antibodies in the people who become infected with it. (Remember?) People infected with strain H5N1 will have antibodies in their blood that bind the H5N1 antigens. We say they are seropositive if they have the specific antibodies. The first person to die of the avian flu (complications) had contact with chickens so we see clear evidence for a bird-to-human link. (The first of its kind!) Not surprisingly that boy had antibodies to H5N1 - not enough to save his life but enough to show that he was seropositive. Now imagine you were part of a family with a 3 year old boy suffering from flu. Considering the mess and awful hygiene that goes with children of this age, along with the supervision, attention and contact needed to make the child comfortable, it's easy to understand why people in the family should be at high risk of catching the flu. The good news is that none of the four members of his family were seropositive. All four were seronegative for H5N1. Therefore, they didn't catch avian flu from the boy even though they would have been prime candidates.

However, one of the 54 health care workers who came in contact with the boy was seropositive for H5N1 and that person does not recall any exposure to poultry. This might be taken as evidence for human-to-human transmission of the virus! Or it might be taken as evidence that the health care worker can't remember when she handled a live chicken. The interesting thing about antibodies and these tests is that you usually remain seropositive for many years, often all your life. How many people do you know who can swear that they've never touched a live chicken? Besides, when they tested 63 people in the same neighborhood, but otherwise not involved with the boy, they found one that was seropositive. Although these numbers suffer from a lack of statistical rigor they hint that one might be seropositive from handling an infected chicken but not remembering it. Also, it's possible to be seropositive without being infected. Why would someone be seropositive without being infected? I don't know, but I do know that tests like these can give false positive results. The tests can say you've been exposed to the strain when in fact you have not. All serology tests (as these are called) have some level of false positive rates and new tests (like this one) often have very high false positive rates.

Contrast this figure (one positive in 54) with the fact that they found 5 seropositive poultry workers among 29 tested (that's 17.2% positive). They also tested 18 pig farmers and found none of them were seropositive. Looks like you are more likely to get avian flu from chickens than from people or pigs. That's why I'm not too worried.

Another reason for optimism concerns the viral genes isolated from the few cases of avian flu in humans. Analysis of their gene sequences show that they are all avian with no sign of genetic reassortment with a human influenza. That's reassuring because if they had found even one gene segment from a human influenza it would mean that someone had been infected by both the avian AND a human flu and that the mixed offspring viruses could be evolving towards a human-to-human means of transmission. (It's difficult to go into the details of how you can tell an avian flu gene from a human flu gene, but suffice it to say that the specific gene sequences are compared and used to identify the species of origin.)

I conclude that if avian flu is jumping from one human to another it is doing so very poorly because all four members of the family are seronegative and the very low number of seropositive people in contact with the child is similar to the frequency of seropositivity in the local population anyway.

How has avian flu progressed since the first outbreak?

In a word, slowly. Indeed, given all the hype, you might think avian flu has been a "disappointment"! Let's take a brief look at the progress of this disease since its outbreak.

By January 1998, half a year since it started, there had been 18 confirmed (by serology tests) cases of H5N1 in humans. Six of them died, so this was a pretty deadly virus, similar to the virulence of H1N1 from 1918 (the Spanish Flu). The original outbreak was deadly but did not cause many deaths when contrasted against the background of deaths that year from other causes.
By January 2009, 248 people have died from the H5N1 in twelve countries. That's a couple dozen people per year.
I'm not worried. However, there is no telling what these viruses may come up with next. After all they are masters of evolution (because they cheat!).

What causes avian flu, in humans, to be so deadly?

The answer lies in a detailed understanding of the genetics of the particular deadly strain and how it affects humans. Not all the details are known but the type of hemagglutinin (HA) is important. The avian influenza hemagglutinin (H5) binds to a receptor called "alpha 2-3 sialic acid receptor" but the normal human influenza HA (H1) binds "alpha 2-6 sialic acid receptors". Human lungs have alpha 2-6 sialic acid receptors near the top of the lungs and alpha 2-3 sialic acid receptors mostly near the bottom of the lungs. That means, when a person is infected with a virus carrying the H1 version, the infection tends to be limited to the upper respiratory tract. That makes it easy to spread but also easy for the body to battle it. Coughing brings up goo from the upper respiratory tract more easily than from the lower respiratory tract, so it is easier to recover from infection by H1. On the other hand, H5 binds to the lower respiratory, making it harder to shift (cough up). This also makes it harder to transmit. This may be why avian flu (H5N1) in humans does not seem to spread to others.
By the way, birds have "alpha 2-3 sialic acid receptors" throughout most of their lungs, so spread H5N1 among themselves fairly well.

OK. What about swine flu virus?

Swine influenza virus (SIV) is the general name for any flue virus in pigs and H1N1, H1N2, H3N1, H3N2 and H2N3 are all common in pigs. SIV usually does not infect humans but some pig farmers have antibodies to SIV. This means that the virus has gotten into the farmer and tried to establish an infection but the person was able to easily mount an immune response to it - so no harm done. (Actually, the person probably got a little ill but shrugged it off as just a "cold".) Pigs act as a reservoir for "human/swine flu" and pigs have been involved in several human outbreaks.

During the 1918 epidemic, pigs were affected too. It is not clear if humans caught it from the pigs or the other way around. After a lot of research on the subject, the mystery still remains as to where the 1918 flu came from! The complete genomic sequence has been determined but we still don't know its origin. Regardless, for about 60 years, people considered swine flu as a problem for pigs and the people who depend upon pigs for a living. It was an H1N1 virus - same designation as the current swine flu but also the same designation as the common, seasonal flu. Remember, you can't judge a virus by its HN name.

In 1976, swine flu killed a solider at Fort Dix and made four of his colleagues very ill but this "epidemic" (I put that in quotes) lasted about a month and never got out of Fort Dix. Another mystery - after all, Fort Dix is not a pig farm! How did this happen? No one knows. But we do know that it killed one out of the five service men and they were healthy, strong adults. Soldiers. Meanwhile, an unrelated swine strain (H3N2) started making the rounds throughout the USA. This resulted in political turmoil and panic. A vaccination program was rolled out and by the time flu season started (October 1976) about a quarter of the US population had been vaccinated. That same month, three elderly people died soon after receiving their vaccination - but it was never established if the vaccine killed them.

It is agreed, however, that the vaccination program was responsible for about 500 cases of Guillain-Barré syndrome (GBS) - a strange neuromuscular disorder, similar to multiple sclerosis (MS). Both GBS and MS are autoimmune diseases. That means, something (a vaccine? a virus?) triggers the immune system to attack the person's own organs, in these cases, the patient's nerves, as if it were fighting an infection. Of the 500 case of GBS caused by the 1976 vaccination program, 25 people died from pulmonary complications caused by the paralysis. The vaccine killed more people than the flu did!
All this caused the vaccination program to be dropped in a couple of months and left many Americans suspicious of vaccination programs.

In 1988 a family in Wisconsin got swine flu and the mother died but other than that, things had gone pretty quiet on the swine flu front.
Then came Mexico City.

On March 18, 2009 surveillance picked up some cases in Mexico City of a particularly nasty flu. Retrospective analysis revealed that this particular strain of H1N1 first evolved around September 2008 and circulated in the human population for several months before the outbreak. It is a new strain produced by the reassortment of four strains; two human, one avian and one swine! (I read a report that swine influenza viruses have the ability to bind both types of sialic acid receptors - but I could not find any information to confirm that).

On June 11, 2009, the WHO declared an swine flue pandemic, moving the alert level to "Phase 6".
(Homeland Security went to color "pinkish", our nuclear forces went to "Defcon 3" and I swear I could hear that annoying "red alert" whine from the starship Enterprise, orbiting overhead! Meanwhile, the media decided that "killer flu stories" would generate excitement among the populous, now bored by the economic crises.)

Is there a vaccine for avian or swine flu?

Sort of. There is an H5N1 (avian flu) and H1N1 (swine) vaccine for poultry and pigs and it is now commonly used to stop the spread of the disease in and between farms, but it is not used in humans.

However, major vaccine companies are gearing up to produce massive amounts of swine flu vaccine for humans. If it is rolled out as quickly as some politicians promise - this summer (unlikely) - it will not have undergone very stringent testing for either effectiveness or safety.

By the way, there is no reason to believe that the "normal" flu vaccine(s) will protect against these (chicken or swine) flus, but the elderly, etc. should still get their annual flu shot/jab to protect against "normal" flu. This standard human vaccine probably does not provide much protection against the deadly strains but it still serves a purpose.

Is there a drug for treatment?

Sort of. The strain of H5N1that killed birds and some people in Asia years ago, is resistant to two antiviral medications commonly used to fight flu - amantadine and rimantadine. To other antiviral medications, oseltanamavir (Tamiflu) and zanamavir (Relenza), might work. All these drugs are by prescription only and must be monitored by a physician. (And, no, I cannot give you a prescription nor do I have any of these drugs.)

By the way, there is good evidence to suggest that flu viruses easily "mutate around" oseltanamavir (Tamiflu), so I would guess that a big roll out (heavy use) of this drug will produce a strain resistant to oseltanamavir (Tamiflu) in short time. On the other hand, there is no evidence that flu viruses can easily circumvent zanamavir (Relenza).

Should I kill my pet chickens, parrot, etc?

NO! You don't have to worry about getting avian flu from your birds. The worry, in general, is that a bird flu will jump into a human but that jump is a rare event - thus not to be feared. However, once that event occurs, the spread from human to human is the next concern. That would trigger a terrible epidemic.

It's a statistical thing. Only one person need be infected by the bird flu for it to take hold but that is an unlikely event. Then another mutation (or series of mutations) is needed to cause it to switch to human transmission and that is a rare event too. So the likelihood of avian flu causing a human epidemic is based upon two very rare and independent events occurring in sequence. That is very, very unlikely. (It is "rare square".) And it is much more likely to occur in Asia and on a poultry farm, where there's a high density of sickly birds tended by people who are more likely to make contact, not among pets.

You are more likely to die of a tetanus infection from a chicken's scratch or lung problems from the bird "poo" or asthma from its feathers than from your pet's flu.

Can I get the flu from eating pork or poultry?

Cooking kills the flu virus so even infected meat is safe if cooked properly. Of course, you should always cook meat thoroughly before eating it anyway! Especially chicken.
It's also unlikely that you would catch something handling their carcasses but you should always wash your hands after handling dead animals. That's just good hygiene.

What if it becomes a human-to-human epidemic?!

That depends. If it is truly deadly, stop worrying about birds and pigs and start worrying about people! There are two things to ask about flu - how easy is it to catch (transmit) and how deadly (virulent) is it? As of 18 July 2009, it looks like the swine flu is being transmitted "easily" among people but it is not terribly nasty. (The opposite of the avian flu.) So, this swine flu is pretty much like the "seasonal" flu that runs around each year. That common-but-not-news-worthy flu season starts in October (in the northern hemisphere), so if you have a flu over the summer of 2009 it could be swine flu! But don't panic. It is not much worse than any other flu - but is more likely to ruin your summer vacation than your winter holidays.

IF (that's a big "IF") it becomes a deadly human epidemic, you should do whatever you can to avoid the flu. Keep out of crowds (total isolation would be best but is impractical) and away from sneezes. Wash your hands frequently when visiting public places (buses, school, etc) and try not to rub your eyes, nose or mouth because that is a common way for the flu virus to get into you.

How long does the virus last (on door knobs)?

The flu virus (particle) is easily destroyed. Sunlight, especially the UV part, and dry air will render the particles non-infectious. And, of course soap will too.
How long it takes to "kill" the virus depends upon the specifics. An hour or two should kill most flu viruses on door knobs (for example) but there might be some individual virus particles that linger for a week. It's hard to say. These kinds of things are a statistical progression, so there are always a little left over after many hours.

Is this hype or is there reason for concern?

Let's put some perspective on this.

Generally speaking, a "killer flu" epidemic occurs every few decades. Some are worse than others. The most recent flu epidemic occurred in 1968 and wasn't too bad. The most deadly flu in recent history killed over 20 million people in 1918 and it was very similar to the virus that we are concerned about now. Today, we have much better medicines and health care (at least in the developed nations) but we also have much more global travel which helps flu to spread. Some experts have been quoted as saying that the next killer flu epidemic could kill more than 100 million people! Maybe they're right - or maybe "100 million" is more likely to get quoted by every newspaper on the planet while "1 to 100 million" just isn't so exciting. And to say it might kill only as many people as the common, seasonal, flu - well that is not very interesting to report.

Here's a headline that you missed - "Two million people die each year from tuberculosis (TB)". That's each year! Spread that out over several decades (the time between killer flu epidemics) and that's a large number of deaths. But TB is, for the most part, ignored by folks who are all worked up about bird/chicken/swine flu. Many TB victims are in underdeveloped countries - another reason TB is ignored. Besides, most TB is easily cured with simple antibiotics found in developed nations. However, multi-drug resistant TB (MDR-TB) is on the increase and very hard to treat. MDR-TB is now found in more than 4% of new TB cases in Eastern Europe, Latin America, Africa and Asia. As the World Health Organization puts it "Given the increasing trend towards globalisation, trans-national migration, and tourism, all countries are potential targets for outbreaks of MDR-TB." (I won't discuss this further but you can Google "multi-drug resistant tuberculosis" to learn more.)

My opinion? At this time I have a feeling of deja vu.

Should I panic?

No, not yet.

If you have a comment or question about influenza feel free to send a Letter to the Editor.

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