What is H5N1?
November 18th, 2010
12:43 PM ET

What is H5N1?

H5N1 sounds like a random collection of letters and numbers, but to doctors who specialize in the flu it spells the name of a fearsome enemy. Unlike even a severe strain of typical or seasonal flu, H5N1 – which is a type of bird flu – causes critical illness or death in a majority of those it sickens. 

A person infected with bird flu typically becomes feverish and within a day or two develops trouble breathing, as the virus lodges in the lower respiratory tract.  A substantial number of patients have diarrhea or other gastrointestinal symptoms. Taken early in the illness, the antiviral medications Tamiflu and Relenza can help, but with or without treatment about 60 percent of all patients die.The H5N1 virus circulates naturally in wild birds, especially ducks and other water fowl.  Spread by droplets in the air and in bodily fluids, it can easily pass to other birds including domestic chickens. Once it gains a foothold in a flock of chickens, H5N1 has been known to kill every bird it infects.

Fortunately, the virus isn’t easy for people to catch. While well adapted to the respiratory system of birds, it lacks the ability to easily latch on to human cells.  Most people who have fallen sick with H5N1 have had close contact with birds – such as cutting up infected chickens – although a handful have been infected by their own family members.

Why the alphabet soup?  The numbers and letters of H5N1 represent specific types of proteins.  The type of hemagglutinin – H – determines to which cells the virus can attach itself, while the neuraminidase protein – N – determines the virus’ ability to make copies of itself.  Because flu viruses mutate quickly and constantly, there are a vast and ever-changing number of genetic subtypes.

New flu strains emerge when an animal or person is infected with two flu viruses at the same time, and the viruses inside the body “swap” parts of their genetic material.  For virus trackers, the nightmare scenario is H5N1 taking genes from a more common flu virus, that would enable it to more easily infect people.

H5N1 cases in humans have been relatively rare, with fewer than 500 cases worldwide since 1997, when the first victims were spotted in Hong Kong.  However, the virus is well-established in bird populations throughout southeast Asia and also in Egypt.  “H5N1 is endemic in the poultry population, and as long as that’s the case, we have to continue to be vigilant,” says Dr. Carolyn Bridges, an influenza expert at the Centers for Disease Control and Prevention who helped investigate the 1997 outbreak. “The hallmark of influenza viruses is their ability to change, and they can do that very quickly and in unpredictable ways.”

soundoff (3 Responses)
  1. Big Bird

    It was horrible!
    I turned a different shade of yellow .....
    I could not work for a week...
    I survived though because I read Lizards Crowins book.........
    empowered patient....................

    November 18, 2010 at 18:59 | Report abuse | Reply
  2. FedFraud

    Wait until the dog and cat flu.

    November 19, 2010 at 01:01 | Report abuse | Reply
  3. waow


    November 20, 2010 at 23:29 | Report abuse | Reply

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Get a behind-the-scenes look at the latest stories from CNN Chief Medical Correspondent, Dr. Sanjay Gupta, Senior Medical Correspondent Elizabeth Cohen and the CNN Medical Unit producers. They'll share news and views on health and medical trends - info that will help you take better care of yourself and the people you love.