Jon Hamilton, NPR
Thai farmer Wirat Sarien, pictured outside his house, says he was careless in disposing of dead chickens, tossing some carcasses in the woods. At the time, he didn't know there was a bird flu outbreak. His entire flock of chickens died.
Jon Hamilton, NPR
Jon Hamilton, NPR
Wicharnchai Piengphon (left), a Thai government investigator of bird flu, consults with a regional official about recent chicken deaths on Sarien's farm.
Jon Hamilton, NPR
A Thai worker collects chickens to be destroyed at a farm west of Bangkok.
Thailand has killed more than 40 million chickens this year in an effort to stop a deadly strain of bird flu, but the virus keeps resurfacing.
The bird flu virus now circulating in Asia is known as H5N1. Such viruses are named according to a standardized convention:
Flu viruses have spikes of proteins sticking out from their surfaces. The types of proteins are used to categorize influenza as belonging to types A, B, or C.
Pandemic viruses are in the A type. Type A flus are blamed for the global outbreaks of 1918, 1957 and 1968.
Strains within type A influenza are further coded into subtypes by a letter and number. (Types B and C have no subtypes.)
The "H" in H5N1 stands for hemagluttinin, a protein that makes the virus sticky so that it can attach to a cell and infect it. The "N" represents neuraminidase, which allows a newly created virus to break out of a cell so that it can infect others. According to the NIH, scientists have characterized 15 H subtypes and 9 N subtypes.
When more precision is needed, scientists use additional coding, listing where the strain was discovered, which lab discovered it and what year it was found. Thus, when the H5N1 virus emerged it was named A/Hong Kong/156/97 (H5N1).
Source: National Institute of Allergy and Infectious Diseases, 2004
Bird flu has infected at least 17 people in Thailand. Twelve have died. Scientists say each human infection increases the chance that bird flu will establish itself in people and cause a global pandemic.
The Thai government has vowed to stop the virus, known as the H5N1 strain, by finding every infected chicken in the country, then killing it and every other chicken in the neighborhood. But as NPR's Jon Hamilton reports, it's proving to be a daunting task.
Thailand has recruited more than 800,000 people to fight avian flu. These workers rely on farmers to report dead chickens. But farmers know a confirmed infection is a death sentence for their entire flock.
Farmers don't get compensated for chickens killed as part of anti-bird flu efforts unless a district official orders the slaughter. That means village officials may delay ordering the culling of infected birds to avoid tensions with local farmers. Some uncooperative farmers have even moved potentially infected birds to protect them from culling.
Major Flu Pandemics in Recent History
1918 strain: H1N1
The most devastating flu pandemic in recent history, killing more than 500,000 people in the United States, and 20 million to 50 million people worldwide, according to the National Institutes of Health. The first U.S. case is believed to have occurred in March 1918 in Fort Riley, Kan. Though often called the "Spanish flu," the best evidence suggests this strain originated in Kansas.
1957-58strain: "Asian flu" H2N2
First identified in China, this virus caused roughly 70,000 deaths in the United States during the 1957-1958 season. Because this strain has not circulated in humans since 1968, no one under age 30 has immunity to it.
strain: "Hong Kong flu" H3N2
First detected in Hong Kong, this virus caused roughly 34,000 deaths in the United States during the 1968-69 season. This represented an increase of a few thousand deaths over the normal yearly death toll from flu. H3N2 viruses still circulate today.
Significant New Flu Strains in the Human Population
When the H5N1 flu strain emerged in 1997, it marked the first time that an influenza virus jumped directly from birds to humans. Researchers linked infections to exposure to poultry markets. Eighteen people in Hong Kong were hospitalized, six of whom died. Since then, several significant new flu strains have entered the human population:
Caused illness in two children in Hong Kong, with poultry being the probable source.
Evidence of infection is found in one person in Virginia following a poultry outbreak.
Caused two Hong Kong family members to be hospitalized after a visit to China, killing one of them, a 33-year-old man. (A third family member died while in China of an undiagnosed respiratory illness.)
Eighty-nine people in the Netherlands, most of whom were poultry workers, became ill with eye infections or flu-like symptoms. A veterinarian who visited one of the affected poultry farms died.
2004 (through October)
The H5N1 virus that first emerged in 1997 has evolved. In its current version, it has caused illness in 44 people in Thailand and Vietnam, 32 of whom have died. Researchers are especially concerned because this flu strain, which is quite deadly, is becoming endemic in Asia.
Caused illness in two poultry workers in Canada.
Caused illness in two infants in Egypt. One child's father is a poultry merchant.