Flu Virus From Bird Infects Boy in Asia
Experts Worried About Global Pandemic
Too many people, eating too many animals, all too crowded together - Doc
By Rob Stein
Washington Post Staff Writer
Sunday, December 14, 2003; Page A03
While the start of this year's flu season has been especially wretched, flu experts say it is not the killer pandemic they have been worrying about for years. They are more anxious about a little-noticed case that emerged last week in Hong Kong, where a 5-year-old boy was infected with a bird flu virus, because that is the sort of event that could spark a long-feared global health emergency.
The child recovered, and so far no one else appears to have been infected. But experts say they are monitoring the situation closely because whenever a new animal flu virus infects a person it has the potential to create an entirely new virus against which humans would be defenseless.
"Every transmission of an avian influenza virus to humans raises the possibility for a pandemic. So we immediately have a red alert," said Klaus Stohr, a top flu specialist at the World Health Organization in Geneva. "The concern is that a new virus with high transmissibility and high pathogenicity could emerge."
The Hong Kong boy's family is in isolation, and officials are anxiously awaiting the results of tests on them and other children who attend the same kindergarten for signs that the virus had spread or mutated. Three family members had a mild cough.
As soon as WHO officials learned of the case, the agency issued a global alert for scientists to be on the lookout for any flu cases caused by viruses that could not be identified, and they rushed samples of the Hong Kong virus to laboratories around the world to begin deciphering its genetic code and developing tests that could identify it quickly if it were to spread.
"We have to treat it seriously," Stohr said. "Fortunately, so far it looks like an isolated case with no human-to-human transmission. But we are concerned."
In the United States, the federal Centers for Disease Control and Prevention responded by issuing an advisory to scientists around the country to watch for any unusual flu viruses and ship them immediately to Atlanta for analysis. So far none have been found.
"As opposed to what we're seeing with this year's flu season, which is, granted, a bad season, what we're concerned about is the beginning of a pandemic of influenza with a new virus that emerges from the animal population," said Scott Harper, a CDC flu expert. "This would be really an entirely different scenario than just having a bad influenza season."
The flu outbreak underway in the United States and Europe is caused primarily by the Fujian virus, which was first detected in the Fujian province of China last year and began showing up widely this fall. Part of the reason officials believe this year's flu season will be more severe than in recent years is that the Fujian virus is from a family of flu viruses known as H3N2, which tend to be more likely than other viruses to cause widespread illness.
The Fujian strain is the result of a slight genetic change that occurred to an H3N2 virus that has been circulating for years. That means people's immune systems have not been exposed to that precise virus before, making them more susceptible to infection. Because it was discovered too late to be included in this year's vaccine -- although a close relative was included -- the vaccine probably is not as protective as it has been in past years.
But most people have had at least some exposure to other H3N2 viruses, making it likely that their immune systems have some power to protect against them.
In contrast, the virus that infected the Hong Kong youngster comes from a family of flu viruses known as H9N2, which usually infect only birds. Most people's immune systems offer no protection from the virus.
"What we fear is that one day a new subtype of influenza virus will emerge -- a subtype that none of us has been exposed to before," Stohr said.
Animal flu viruses jump to humans on a regular basis. Most of the time, they do not cause major outbreaks because they are not well suited to humans -- they cannot spread easily among people or do not make people very sick.
But periodically animal flu viruses combine with a human virus and produce a hybrid that spreads easily among people and makes them very sick. That is what is believed to have occurred in 1918-19, when the "Spanish flu" caused a devastating global pandemic that killed at least 20 million people.
"The virus has to be capable of spreading well in humans. If it's not able to do that, it will stop spreading in the human population. If it is able to do that, you'll have a pandemic," said the CDC's Harper. "That's why whenever we hear about one of these cases, we get concerned."
One scenario is that the avian virus that infected the Hong Kong boy could intermingle with the Fujian strain. The last time a bird flu virus combined with a human virus was in 1968, sparking that winter's Hong Kong flu pandemic. Today's Fujian strain is a descendant of that strain.
The Hong Kong incident marks at least the third time this year that bird flu viruses have jumped from birds to humans. Two people died in Hong Kong after getting infected with a bird virus in China. An outbreak of flu in chickens in the Netherlands was brought under control after the government killed 32 million birds, but not before more than 80 people were infected, including a veterinarian who died. And on Friday, South Korean health authorities announced they are investigating a worrisome suspected outbreak of highly contagious avian flu among chickens near Seoul. No people are known to have been infected, but authorities said they had killed 5,000 chickens on a farm to try to stamp out the disease.
Investigators are urgently trying to determine how the Hong Kong child got infected.
"We have no clue where it came from," Stohr said. "We are concerned that this virus is still present in the avian population in southern China."
"Every transmission of an avian influenza virus to humans has the potential for a global pandemic. It's just a question of time and statistical probability before there will be one person infected with a human and avian virus, and a virus of high transmissibility and pathogenicity will occur."
washingtonpost.com |
