Tracking Asia's Deadly Bird Flu Outbreak
Scientists work to determine why it seems more lethal than other strains
WEDNESDAY, Feb. 25, 2004 (HealthDayNews) -- One victim was a devotee of cockfights who often handled the birds and frequently passed through a live poultry market on his way to school.
Another was a farmer who cared for sick ducks and chickens in his home, located in a district of Vietnam rife with ailing birds.
A third person, a woman, bought a duckling that came down with diarrhea. When the young bird died she buried the animal, only to dig it up again and re-bury it. She also ate nearly raw duck eggs, a local delicacy.
These are three of the people who succumbed to the bird flu that is sweeping through Vietnam and other Asian countries. The virus, avian influenza A (H5N1), seems to be a remarkably lethal pathogen, killing people -- many of them young -- with no health problems.
Through Monday, the World Health Organization (WHO) had recorded 32 human cases of bird flu, among them 22 deaths, limited to Vietnam and Thailand. Health officials believe every case so far has involved a person who came into direct contact with a sick bird or its excretions.
But experts also say the absence of any evidence of human-to-human transmission of the deadly virus doesn't mean it can't or won't happen -- or hasn't already.
"This particular infection is clearly difficult to catch and seems to come about following very close contact with poultry, and there is no evidence of human-to-human transmission among our cases," says Dr. Jeremy J. Farrar, an infectious disease specialist at the Hospital for Tropical Medicine in Ho Chi Minh City, Vietnam.
"However, if you are very unlucky and do get infected with this strain, it obviously causes a very severe disease with a high mortality," Farrar says.
Farrar and his colleagues have compiled case studies of 10 Vietnamese patients, eight of whom died. They report their findings in the March 18 issue of the New England Journal of Medicine. The journal posted the research on its Web site on Feb. 25 "because of the possible public health implications."
Eighty percent of the Vietnamese patients who contracted the bird flu died of the infection. By comparison, an outbreak of avian flu last year in the Netherlands caused only one death among 89 confirmed cases.
Farrar says it's not yet clear if the current strain is much more lethal than previous avian influenza germs. There may have been many more human cases with far less serious symptoms that have gone undetected, he says, so the actual mortality rate may be low.
"Hopefully when the outbreak is over we can look at all the confirmed cases and see what the complete clinical spectrum is and what the overall mortality rate is," he says.
Of the 15 known strains of avian flu, health officials say, the H5N1 form is especially worrisome for its ability to mutate quickly and to pick up genes from other flu strains. And as the latest outbreak shows, the virus certainly can harm humans.
In addition to Vietnam, the H5N1 strain has been identified in poultry and other birds, including a peregrine falcon, in Cambodia, China, Hong Kong, Indonesia, Japan, Laos, South Korea and Thailand, according to the U.S. Centers for Disease Control and Prevention.
Discovery of the infection has prompted governments to order the mass slaughter of sick birds and birds exposed to the virus to stop further human infection and prevent a pandemic. During a 1997 bird flu outbreak in Hong Kong, for example, officials ordered the culling of the region's entire poultry population of some 1.5 million birds in three days, a step the WHO credits with possibly averting a pandemic.
Farrar says Asian governments have acted appropriately in the face of the outbreak.
"It is obviously very difficult but there has been very active culling of poultry and birds and widespread dissemination of the information in all the media and I think now the situation is reasonably well-controlled," Farrar says. "The crucial issue is to maintain the current containment and not relax too soon and allow the infection in chickens to become endemic and established."
Several strains of avian flu have also cropped up in the United States, including Delaware, New Jersey, Pennsylvania and Texas. These strains aren't the same as the H5N1 organism blamed for the human deaths in Asia. The H5N1 strain was responsible for the 1997 Hong Kong outbreak. Human-to-human transmission was not observed in that episode, in which 18 people fell ill and six died.
But bird flu viruses have made the jump to people and then managed to spread among their human hosts. The savage 1918 flu pandemic, which claimed between 40 million and 50 million lives, is one example.
Dr. Mark S. Klempner, a Boston University microbiologist and co-author of a commentary on the new study, says he doesn't believe the current outbreak is headed for pandemic status. But the study justifiably raises the prospect with the medical and public health communities. And it signals doctors to be alert to suspicious infections -- not just bird flu but SARS, monkey pox and other emerging diseases, he says.
"People in the medical community are very aware that when they see a respiratory illness they need to be aware of the epidemiology," Klempner says.
Scientists don't know how a bird flu strain could acquire the genetic wherewithal to pass from person to person. To do so, the organism would probably require an intermediary species, such as pigs, that's prone to both human and bird influenza.
"The thinking is that a bird flu virus can infect a non-human host, and a human flu virus can infect the same host, they can mix, and what comes out of there can bind to human cells. We believe that that happens, but the myth is that it's pinned on a pig," Klempner says.