Of birds and men
A deadly virus is brewing in Asia. Could this be the next killer pandemic?
[map of Asia]
All past and present H5N1 outbreaks in poultry: China; Hong Kong; South Korea; Japan; Laos; Malaysia; Indonesia
H5N1 detected in humans and poultry: Thailand; Cambodia; Vietnam
Two known cases were diagnosed with no symptoms, suggesting that humans could become carriers of H5N1.
SCENARIO D: PANDEMIC
Scientists fear H5N1 will morph into a new virus with the deadliness of avian flu and the transmissibility of a human strain, allowing the new virus to spread quickly among people. How it happens: In a person simultaneously infected with H5N1 and a human flu strain, the two viruses can mix their genes, or "reassort," producing a new strain with the most dangerous traits of both.
DEVELOPING A VACCINE
H5N1's surface bristles with two types of protein spikes. One type, hemagglutinin (HA), helps the virus stick to a cell to cause infection. The other, neuraminidase (NA), enables newly formed viruses to leave a host cell.
A successful vaccine will cause the body to make antibodies against these two types of protein spikes on the surface of the virus.
Then the antibodies attach to the protein spikes of the invading H5N1 virus, disabling its ability to infect.
Antibodies created by a person's exposure to other flu strains will not protect against H5N1.
HA protein spike
NA protein spike
THE FLU OVER TIME
The Spanish flu pandemic kills more than 500,000 people in the U.S. and as many as 50 million worldwide.
The Asian flu pandemic kills 70,000 in the U.S.
The Hong Kong flu pandemic takes about 34,000 lives in the United States
For the first time, an influenza virus spreads directly from birds to people at poultry markets in Hong Kong: 18 are hospitalized, 6 die.
In Hong Kong, 2 cases, 1 fatal. The sudden death of 19,000 chickens on one farm in South Korea leads experts to suspect an epidemic.
Cambodia: 1 case, fatal; Thailand: 17 cases, 12 fatal; Vietnam: 51 cases, 33 fatal. WHO says domesticated ducks could serve as a "silent reservoir" of H5N1.
Sources: CDC; NIH; Andrew T. Pavia, M.D.; University of Utah; World Health Organization; news reports
Written by Stephen Rountree & Nicole Schofer, timeline by Katy Kelly-- USN&WR
Graphic by Rod Little-- USN&WR
With Elizabeth Querna, Bill Bainbridge, Susan Brink and Nisha Ramachandran