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My pseudonym is accurate. I am a practicing physician. As such, I thought I'd share my understanding of the emergence of this new "Swine Flu" outbreak. I'm not a virologist, nor an infectious disease specialist, but the story of this influenza outbreak seems straightforward enough.

Influenza viruses seem to percolate and transmit in animal populations such as birds (avian) and pigs (swine), and periodically acquire the ability to infect people (such as SARS). Viruses tend to mutate quickly, and this is why the flu vaccines we make each year change: the viral antigens (proteins or glycoproteins that our immune system can "see") change from year to year. So the vaccines have to change too, enabling our immune system to "be ready" for the mutated viruses.

On the other hand, sometimes totally new viruses emerge: new combinations of swine, avian, and human influenza viruses. When this occurs, as is the case now, no previous vaccine or previous infection will afford any protection from the new virus. The "Swine Flu" virus now spreading around the globe is a unique and novel combination of swine, bird, and human viruses.

Unlike SARS, which was an avian virus with relatively low human to human transmission, this new virus appears to readily transmit between humans. Fortunately, except in Mexico, this new virus has, so far, produced a relatively mild case of the flu. There is only one report of a hospitalization in the U.S., but no serious illness. Also, no increase in ER visits has been noted, which the CDC and local health departments monitor closely.

Fortunately, researchers report that this new virus does respond to Relenza (NYSE:GSK) and Tamiflu (OTCQX:RHHBY and GILD), the two anti-viral compounds that are readily available and in mass production. That's the good news, so far. A new virus that has produced a mild case of the flu outside of Mexico, but, does transmit easily from person to person.

The fear. The worst case scenario and the one that keeps some infectious disease specialists up at night is the so-called Spanish Flu of 1918-1920. Researchers are still unclear about the precise orgins of the Spanish Flu Pandemic, but it appears to have originated as an avian virus, done some genetic recombination in pigs, and acquired the ability to infect and transmit between humans around 1918. The Spanish Flu virus was highly contagious, and had a mortality rate of up to 2% of infected individuals. A typical flu has a mortality rate of about 0.1%.

Unlike a typical flu outbreak, which tends to have the highest rates of mortality in the very old and the very young, the Spanish Flu had the highest mortality in those that were the healthiest: young adults. Researchers believe that the Spanish Flu killed by a couple of different mechanisms, including direct viral destruction of the lungs, or, triggering a massive immune response against the virus in the lungs, or, by setting the stage for a secondary bacterial infection after the virus itself had faded (there were no antibiotics in 1918).

The morbidity and mortality of the Spanish Flu of 1918 was somewhat obscured by World War I at the time. But the world wide pandemic's effects were staggering: estimates of up to 50 million dead world wide, with some localities all but wiped out, striking even the most isolated villages in the Arctic and the South Pacific.

The current "Swine Flu" of 2009 appears to transmit readily from person to person, but, except in Mexico, has been mild and without mortality. The fear is that the virus could mutate into a far more virulent and potentially lethal form. Indeed, the Spanish Flu of 1918 had a "first wave" in the spring of 1918, as a fairly mild viral inflection that was noted in just a few newspapers at the time. It re-emerged in the Fall of 1918 as perhaps the most lethal human to human infection in recorded history.

The closest historical analogy to the human toll of the Spanish Flu of 1918 is the Bubonic Plague that killed about 1 in 3 Europeans in the 1300s. The Plague was caused by a bacterium transmitted from rodents to humans via fleas. The Bubonic Plague is treatable with conventional antibiotics and makes an occasional appearance in real life, as well as medical school exams and television shows.

It is too early to be able to write off the current "Swine Flu" as a non-event. The "Mexican Flu of 2009" is a novel flu that has resulted in some mortality in Mexico, and is spreading rapidly throughout the world. Hopefully, the virulence of the virus will remain low, a vaccine will be manufactured and distributed, and there won't be much more to it than that.

Disclosures: None currently

Source: Swine Flu: Current Status and Worst Case Scenario