Rapid onset of symptoms and Death

There was recently a discussion on the Rhizalabs Flutracker message board about the recent (as of mid-June) spate of rapid deaths in young, healthy people. I posted an explanation of why viral pneumonia from influenza seems to cause rapid onset of illness and death (often less than 24 hours) versus more "normal" bacterial pneumonia triggered deaths. This was apparently a well-received explanation as it was requested I repost it periodically. I am posting it here so I can have easy access to it. Note there may be some finer technical details that are off, but I believe this is largely good enough for the layman.

From various things I have read it seems the immune system treats a viral infection of the lungs much differently than it does a bacterial infection. Normally, your immune system has to fight off bacteria by having certain types of immune cells eat (phagocytose?) the organism. This can be done without the the extremely lethal parts of the immune system.

But a virus enters the cell and hijacks the internal mechanisms in order to make more virions. The body must kill parts of itself, either by triggering the infected cell to die (apoptosis?) or outright killing it. Whena virus infects the lungs the body has to mount an attack with essentially its full arsenal. This leads to a cascade that can result in, as I understand it, the spongy material of the lungs being transformed into scar tissue.

The progression is viral pneumonia -> cytokine storm -> ARDS -> (multiple organ failure?) The cytokine storm is a result of the viral pneumonia and ARDS and multiple organ failure are the consequences of the cytokine storm. This all happens very quickly.

Bacterial pneumonia takes advantage of the weakness in the body generated by the viral infection, and typically takes longer to develop. This is the cycle of being sick, getting better, then taking a turn for the worse.

Is this a Pandemic or not?

The short answer is yes.

The long answer requires an understanding of what a pandemic is.

From the Wikipedia article:

Definition

According to the World Health Organization (WHO), a pandemic can start when three conditions have been met:[1]

* Emergence of a disease new to a population.
* Agents infect humans, causing serious illness.
* Agents spread easily and sustainably among humans.

A disease or condition is not a pandemic merely because it is widespread or kills many people; it must also be infectious. For instance, cancer is responsible for many deaths but is not considered a pandemic, because the disease is not infectious or contagious.

This is a generic pandemic definition, and not specific to influenza.

For the case of an influenza pandemic we will add the following:

Influenza pandemics occur when a new strain of the influenza virus is transmitted to humans from another animal species. Species that are thought to be important in the emergence of new human strains are pigs, chickens and ducks. These novel strains are unaffected by any immunity people may have to older strains of human influenza and can therefore spread extremely rapidly and infect very large numbers of people. Influenza A viruses can occasionally be transmitted from wild birds to other species causing outbreaks in domestic poultry and may give rise to human influenza pandemics.

So, what are we dealing with? The novel influenzavirus A(H1N1) that is currently circulating is, by definition, a new virus in humans (though containing genetic material from previous human strains of influenzavirus type A), it definitely infects humans and can cause serious illness, and is capable of sustained spread between humans. Furthermore, it is a new virus from a different species (pigs). Therefore, despite the WHO's attempts at not declaring a full pandemic, the "classical" conditions are met.

It bears repeating, a pandemic does not have to be highly lethal, it has to infect humans in large portions of the world. The "Swine Flu" is doing just that, and the virus doesn't care what people say about it.