Munich

The death on 17 April of a veterinarian who contracted flu from chickens in the Netherlands has heightened concerns about the threat posed by the disease.

Since the outbreak of the illness in late February (see Nature 422, 247; 2003), 18 million chickens have been culled in the Netherlands — including six million killed last week close to the German border. But the flu has now spread to birds in Belgium, prompting the slaughter there of hundreds of thousands of chickens.

Transmission of the disease to humans remains a major concern. Ron Fouchier, a virologist at Erasmus University in Rotterdam who monitors human cases of the avian virus, says that he “remains very worried” about the outbreak.

Since 28 February, 83 people have become infected with the virus, known as H7N7. Most have suffered only conjunctivitis, but eight have developed mild flu-like symptoms. The vet, who was from Den Bosch, died from pneumonia.

“The numbers are, of course, small — but the death rate among those with flu-like symptoms is similar to that for the Hong Kong outbreak in 1997,” says Fouchier. In Hong Kong, 18 people suffered flu-like symptoms and six died from a bird-flu virus identified as H5N1.

Neither H7N7 nor H5N1 spreads rapidly between humans, so a pandemic is thought to be unlikely. “But we don't have things under control,” Fouchier says.

The number of new cases in humans has slowed in the Netherlands since 10 March, when at-risk workers began taking the antiviral drug Tamiflu. Belgium has also introduced measures to protect people working with chickens.

Marion Koopmans, a spokeswoman for the RIVM, the Netherlands' public-health laboratory, warns that other countries should be on alert, particularly as the chicken cull involved several thousand foreign labourers.