New flu, old lessons

It feels as if we’ve been here before: New type of influenza is identified, virus begins to spread, public health officials sound the alarm.

This time it’s influenza A (H3N2), which apparently is being transmitted from pigs to humans. As of Thursday, more than 120 cases had been confirmed in the United States since July. The new form of swine flu has been found in four states and is overwhelmingly occurring among young people. A common denominator seems to be state and county fairs where teens are handling or in contact with hogs. Some farmers and veterinarians also have fallen sick.

Should we be worried? By all accounts, at least so far, this new type of influenza virus doesn’t appear to cause severe illness. It seems to have been around for awhile; the first human cases actually were identified a year ago.

Naysayers might write it off as a big deal over nothing, the same way some felt the H1N1 pandemic of 2009 was vastly overblown. Perhaps we shouldn’t be too quick to dismiss it, though – if for no other reason than the reminder it provides of the wily nature of the influenza virus and microbes in general.

Some years ago I attended a crash course on pandemic influenza that included an overview of how readily the flu virus mutates, circulating among various species, swapping bits of genetic material and shuffling the deck in a perpetual evolutionary process. It’s the main reason why flu vaccines need to constantly be updated and why the flu shot you received five years ago might not be very effective anymore against the flu viruses currently in circulation.

For an illustration of just how crafty the virus can be, here’s CNN’s explanation of how the H3N2 swine flu variant arose:

What makes this new version of the H3N2 flu virus different is that it has picked up a gene from the novel H1N1 flu virus that became a pandemic three years ago. This can happen when a person or an animal is exposed to two different viruses at the same time.

Somewhere along the line, H3N2 and H1N1 viruses were present in a mammal at the same time, and the “matrix-gene” (or m-gene) from the H1N1 pandemic virus was picked up by the H3N2 swine flu, creating a new variant version of H3N2.

It is this m-gene that has experts on the lookout, because the presence of the m-gene can make it more easily transmissible to humans.

See what the virus did there?

Even if it’s not an especially severe form of influenza, H3N2 nevertheless has the potential to make many people sick. A vaccine that would offer protection is in development but hasn’t hit the market yet. Widespread flu can lead to absenteeism at work and school and overflowing doctor’s offices. Inevitably, some of the people who get the virus will be particularly vulnerable and could end up becoming extremely sick.

We have only to look around us to see that the battle against infectious diseases is still going strong: Whooping cough. HIV. Ebola. Tuberculosis. Methicillin-resistant staphylococcus aureus. Although people don’t die of infectious diseases in anywhere near the numbers seen 100 years ago, microbes remain very much a global presence to be reckoned with.

They’re incredibly tenacious and adaptable. In a weird sort of way, you almost have to admire the influenza virus for being so ingenious, so mutable. In spite of all the tools constantly being developed to fight them, flu viruses and their companions in the germ world have figured out how to outwit humans over and over.

The early lesson from the new H3N2 swine flu variant? Where microbes are concerned, it’s not a good idea to get too complacent.

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