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New swine flu puts U.S. on alert

Mexican Federal Policemen wore masks in Mexico City last Saturday.
REUTERS/Felipe Leon
Mexican federal policemen wore masks in Mexico City on Saturday.

In case you were in a coma over the weekend, the Vikings drafted Florida wide receiver Percy Harvin, and an outbreak of swine flu in Mexico City has led to what U.S. officials are calling a “public health emergency” north of the border and beyond.

Both are the source of intense speculation. I’ll leave the pigskins to somebody else. Here’s what we know, and don’t know, about this swine influenza outbreak.

There’s nothing distinctive about the symptoms of swine influenza infection. As with human influenza infections, high fever, headache, severe muscle aches, fatigue and dry cough are the primary symptoms. Occasionally, more often in children, vomiting and diarrhea can develop, but it is limited; the poorly named “stomach flu” really has nothing to do with “the flu” (influenza).

While the strain isolated in Mexico appears to be new, swine influenza has been around a long time, and as the name suggests, primarily infects pigs. Over 25 percent of pigs worldwide have antibodies against this type of swine flu, and as the Centers for Disease Control and Prevention (CDC) reports, the pork industry deals with flu outbreaks routinely.

Nationwide there is usually one human swine flu case reported every 1-2 years, typically in people with close contact with pigs. Rarely, a person infected by a pig can pass the infection on to another human, but generally not beyond a chain of three individuals.

This strain is a unique combination of genes
Laboratory work confirms that this strain of swine influenza is a new kid in town, a unique combination of pig, human, and avian genes that’s never been documented. While this particular combination might be novel, the process it took to generate it is not, as pigs have historically been a key breeding ground for new influenza virus strains. If a pig becomes simultaneously infected with an avian flu virus and a human flu virus, the two strains may trade gene segments and, voilà, a new breed of pestilence is born. A small change in a virus’ genetic makeup is called “antigenic drift.” A dramatic change is referred to as “antigenic shift” and has the makings of a pandemic, depending on what capabilities the reshuffled genetic deck brings with it.

Having a novel genetic code doesn’t necessarily make a virus more virulent. In simplistic terms, a virus needs to be capable of attaching to the cells of the host’s respiratory tract, gain entrance to that cell and reproduce using the host cell’s genetic machinery, and evade the host’s immune defenses long enough to launch its progeny back out into the world.

Because different influenza strains often appear fairly similar to each other immunologically, having immunity to one strain can sometimes afford partial immunity to a different strain. Although this year’s flu vaccine includes a strain of influenza type A, subtype H1, N1, the same make and model as this new swine flu strain, the viruses are otherwise very different; so according to the CDC, this year’s vaccine is unlikely to be protective.
From infective standpoint, it’s clinically potent
Whatever unique genetic properties this new strain of swine flu has, from an infective standpoint it has shown itself to be clinically potent. With cases now being confirmed in California, Texas, New York, Ohio and Kansas, in people with no apparent direct pig contact, this particular strain appears to have the hardware to move directly from human to human, no middle pig required.

Unfortunately, the virus has also shown itself to be lethal, although we won’t know exactly how lethal until we understand how many people have actually been infected. As an example, early reports on the initial West Nile virus outbreak in New York City in 1999 included only those who were sick enough to end up in a clinic or hospital. By checking antibody levels to the virus in blood samples from the general public, it became clear that the vast majority of those infected had either very mild symptoms or none at all.

With this current strain of swine influenza, we have a numerator — over 100 deaths in Mexico, but it will take a lot more detective work to find the denominator and define the risk. Of the 20 confirmed U.S. cases, only two required hospitalization. It’s unclear why there is a discrepancy in lethality between cases in the United States and Mexico; perhaps the difference is more statistical/epidemiological than real.

According to CNN, the cases confirmed in the United States and Mexico “were enough of a concern for Andorra Vassiliou, the European Union’s health commissioner, to recommend against travel to North America. People ‘should avoid traveling to Mexico or the USA unless it is very urgent for them, Vassiliou said.” The report also noted that Dr. Richard Besser, acting director of the CDC, “said Vassiliou’s warning was ‘not warranted.’ “

Another unexplained aspect: age of patients
Another unique but unexplained aspect of this swine flu strain is the age of those most strongly afflicted — older children, young adults, whereas typical flu strains are the most dangerous to the very young and the very old. It’s all speculation at this point, but one hypothesis is that some of the deaths seen in otherwise healthy, robust adults is because their immune response to the virus is so powerful as to be counterproductive. It’s as if the fire department knocked down the whole house to put out a kitchen fire.

There is some good news in all of this. The swine virus appears to be sensitive to two anti-influenza medications, which, if given early, can curtail symptoms and infectivity. It can be prevented by all of the usual measures: good hand washing, sneeze and cough control, and  isolation of those infected. Also, we’re getting late in the flu season, so the virus will have a hard time generating a head of steam, since for unclear reasons, influenza remains a winter-season phenomenon.

If you have influenza symptoms and a travel pattern that puts you at risk, you should call your doctor and be screened. I talked with officials at the Minnesota Department of Health who said it’s still uncertain whether the standard nasal swab testing being done in clinics and emergency rooms will reliably detect this strain of swine flu (does a negative swab really put you in the clear?). The MDH believes it will work, but CDC officials are testing these various screening products, and in the meantime, all specimens are being sent to MDH for more definitive analysis.

Related: Here is a Google map plotting suspected and confirmed cases of the new swine flu.

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Comments (7)

  1. Submitted by Nancy Hokkanen on 04/27/2009 - 12:40 pm.

    Two related links:

    Mexican Lawmaker: Factory Farms Are “Breeding Grounds” of Swine Flu Pandemic

    LATimes: Swine flu ‘debacle’ of 1976 is recalled,0,1182080.story

  2. Submitted by Glenn Mesaros on 04/27/2009 - 12:41 pm.

    Mexican authorities today announced that all public and private schools in Mexico City, the state of Mexico, and San Luis Potosi would remain closed until May 6, in an effort to prevent the spread of the swine flu which has already killed 81 people in that country. Likewise, all sports and entertainment events, as well as the celebration of Sunday religious services, have been suspended indefinitely.

    But even as the government was taking these minimal, appropriate public health measures, the Health Secretary of Mexico City, Armando Ahued, had to admit today that the scheduled major cuts in water supplied to Mexico City residents and businesses, which are planned for May 1-4, would likely seriously worsen the spread of the deadly influenza. The water cuts are due to a drought in Mexico, and dangerously low water levels in the Cutzamala system and related dams, which in turn is the result of decades of disastrous disinvestment in basic economic infrastructure, especially urgently needed water projects.

    Leading U.S. economist Lyndon LaRouche today put the crisis into broader, sharper focus:

    “What’s the mystery?” about the high morbidity rates of the swine flu in Mexico, as compared to the U.S. “Go through the country, and what do you think the risk factors are that define that? It’s as obvious as hell!”

    Mexico’s physical economy has been torn to shreds over the last 25 years of British free trade and globalization policies, especially under NAFTA. Food production and consumption have plummeted. Poverty and unemployment have grown dramatically. The population’s nutritional and overall immunological levels are sinking rapidly, and drug consumption among youth is rising dangerously. Over the last 25 years, 13 million Mexicans fled to the U.S. as economic refugees, in desperate search of sustenance, and now millions of them are being driven back to Mexico as the U.S. economy sinks into deep depression. They are returning to no jobs, no health care, no infrastructure—and, worst of all, no hope.

    “What is happening in Mexico is a result of the operation against Jose Lopez Portillo,” Mexico’s nation-building President from 1976 to 1982, who allied with Lyndon LaRouche to try to defend his country against financial warfare by the City of London and Wall Street. “Some people in Mexico today,” LaRouche explained, “will say: ‘Well, we couldn’t do this, we couldn’t do that…’ You couldn’t do this, because of what was done to Lopez Portillo. You are paying the price for trying to destroy Lopez Portillo. You try to destroy the President of Mexico, you demoralize the country, and now you wonder why you’ve got a problem? This is the time to revive the spirit of Lopez Portillo, and unite all the patriots of Mexico in one bucket,” LaRouche said.

  3. Submitted by T J Simplot on 04/27/2009 - 02:13 pm.

    Very informative article Dr. Bowron. Thank you. I’m still a little unclear as to how you actually die from the flu. Dehydration?

  4. Submitted by Meshach Weber on 04/27/2009 - 04:43 pm.

    I believe that they are seeing a distinctive “early warning” symptom; a sudden onset of sever dizziness.

  5. Submitted by Dwight baker on 04/27/2009 - 04:45 pm.


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  6. Submitted by Carey Page on 04/27/2009 - 07:20 pm.

    The explanation for the swine flu virus with avian and human markers misses the mark. In Asia, it is not uncommon for swine influenza virus to have both swine and avian markers. In that setting, both swine an poultry are co-held in small family plots – in close quarters. In Mexico, the situation is different. The Mexican swine industry is much like the United States: large feed lots. There is little or no co-holding of poultry and swine. I think there is the distinct possibility that this is an engineered virus set afield in a third world country that is a travel hub for the world. This may be the next Black Swan event!

  7. Submitted by Dwight baker on 04/30/2009 - 03:22 am.

    Carey Page says BLACK SWAN EVENT —- You know Carey these days WHO CAN YOU TRUST?

    Seems to me down her on the border where we Anglos try to speak TEXMEX — we have been kicked around and most beleive NO ONE CAN BE TRUSTED.

    Back to SWINE FLU—it was as you said a concocked potion. Will it kill all the underlings I think not. WHY —- MY GOD IS NOT TO BE MOCKED.

    Saying nobody is going to rule the whole world but HIM.

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