The Hong Kong Flu

Dateline: 02/05/98

Sometimes the old rules don't apply. We usually expect there to be a somewhat orderly progression of virus mutations before human infection. Viruses usually pass through other mammals, such as pigs, before being able to infect humans. Such was not the case with the outbreak of the Hong Kong Flu. The virus strain, named H5N1, was transmitted directly from poultry to humans. Interestingly enough, this strain, first discovered in South African birds in 1961, was able to infect humans without first passing through the normal adaptation process in mammals. Before this transmittal from bird to human, only other strains had been shown to cause the flu in human beings.

Strains don't usually change dramatically, but with only slight variations, a process known as antigenic drift. The immune system can defend against these similar versions. But in the case of H5N1, with the jump from birds to humans, the human immune system couldn't adequately cope, rendering the virus particularly harmful.

The first sign of the virus in humans was found in May of 1997 in a small boy. It is not clear how he was infected. At least six people have since died from the disease. Health officials worried that if the virus were capable of being transmitted from human to human, a worldwide pandemic could result. Fortunately, that didn't seem to be the case.

The Centers for Disease Control (CDC) in Atlanta is working on developing a test for the strain and on the mechanism of how the strain was transmitted directly from bird to man. Similarly, two weeks ago, scientists announced that they had decoded the virus's entire genome. This was particularly impressive given the limited time span from the first infection.

After attempting to contain the spread of the virus through strict hygienic measures, officials decided, as a precautionary measure, to slaughter an estimated 2 million chickens to prevent further spread.

What do you think? Does this portend new troubles in fighting virus strains? Are we seeing the start of a particularly virulent pandemic? Visit the Biology Forum and join the discussion!

For additional information see:

• CDC: 'Bird flu' Likely Spreads Through Human Contact
  Report on the Hong Kong Flu from the Centers for Disease Control.