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Avian Flu Outbreak Sets Off Alarm Bells

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Science  02 May 2003:
Vol. 300, Issue 5620, pp. 718
DOI: 10.1126/science.300.5620.718

The economic ramifications seemed bad enough. An epidemic of avian influenza virus roaring through Dutch poultry farms for the past 2 months—more than 20 million chickens have already been slaughtered—is expected to cost hundreds of millions of dollars. But in recent weeks, public health officials already on edge about SARS have reported an unexpected human health toll as well, sparking worries that the disease may transform into a global flu pandemic.

Fortunately, say flu experts, the virus, which belongs to a strain called H7N7, is not very efficient at person-to-person transmission. But there is a small chance that it could become more contagious if it evolves over time or recombines with a human flu strain. The consequences, however unlikely, could be catastrophic, says virologist Klaus Stöhr of the World Health Organization (WHO) in Geneva. Labs participating in WHO's Global Influenza Surveillance Network are already developing a vaccine against the virus. “We have to give this top priority,” says flu scientist Robert Webster of St. Jude Children's Research Hospital in Memphis, Tennessee.

Since it was first detected on 28 February, the outbreak of the so-called highly pathogenic avian influenza has spread to more than 240 farms in central and southern regions of the Netherlands and to several more in neighboring Belgium.

Avian influenza has loomed as a major human health threat since a strain called H5N1 sickened 18 people and killed six in Hong Kong in 1997. Earlier this year, the same strain killed a 33-year-old man, also from Hong Kong, and sickened his son; beyond that, there are no human cases known (Science, 7 March, p. 1504). H7N7 and its close relatives seemed less worrisome because they had caused very little human disease in past outbreaks, says Eric Claas, a virologist at Leiden University Medical Center in the Netherlands who helped identify the H5N1 strain. Indeed, in a 5 March letter to the Dutch Parliament, agriculture minister Cees Veerman called the human health risks “negligibly small.”

Bird watching.

Scientists are closely monitoring an avian influenza outbreak that could spark a pandemic.

CREDIT: FRED ERNST/AP

He was wrong. More than 80 poultry workers and others have developed conjunctivitis, an eye infection caused by the virus. In at least three cases, there's strong evidence that the person directly exposed transmitted the virus to a family member. And on 17 April, a veterinarian who had visited a poultry farm died of pneumonia in a hospital; an autopsy showed massive amounts of avian flu virus in his lungs, and other pneumonia-causing agents were ruled out.

The vet had not taken oseltamivir (better known as Tamiflu), an antiviral drug recommended for anyone potentially exposed to the virus, which was “probably a bit sloppy,” Claas concludes. Still, the severity of his disease is “very unexpected,” Claas says, as is the number of people with conjunctivitis. Experts do not know why the virus is more aggressive than it was previously known to be.

To reduce the risk of the avian strain recombining with a human flu strain, which could happen in someone who is infected with both, authorities are urging poultry workers to get vaccinated against the currently circulating human strains. But recombination can also occur in pigs, notorious influenza mixing vessels that are thought to have spawned the pandemics of 1918, 1957, and 1968. Researchers have already found antibodies against the virus in Dutch pigs—“a big concern,” Webster says.

Stöhr, who also coordinates the scientific battle against SARS (Science, 11 April, p. 224), says that Dutch and Belgian authorities “are doing the right thing” by stressing the importance of antivirals and flu shots. Compliance and rigorous surveillance are crucial, he adds. In WHO's worst-case scenario, the virus evolves to transmit efficiently among humans, infects 10% to 25% of the world's population in a matter of months, and, like H5N1, has a death rate of 30%. That would make SARS look benign.

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