As the northern hemisphere gears up for the annual flu season, another exotic strain of the disease has turned up in Hong Kong. Although health officials are anxious not to cause panic, the Hong Kong strain is being monitored closely because it seems to have jumped from pigs-the animals thought to have been the origin of the 1918 Spanish flu pandemic that killed an estimated 20 million people worldwide.
New strains of flu turn up each year. Most are variants of existing viruses and so pose no special problems. But every few decades, a radically different virus comes along, triggering a pandemic that can kill millions across the globe; the last two were in 1957 and 1968. These killer strains are thought to come from either pigs or poultry.
The latest alarm was sounded after a 10-month-old girl was admitted to Hong Kong's Tuen Mun hospital in late September. Although she was successfully treated, her virus bears all the molecular hallmarks of a strain from pigs. The finding is worrying because analyses of preserved tissue from victims of Spanish flu suggest that it jumped from pigs to people (New Scientist, 29 March 1997, p 20).
"We're monitoring the case very carefully for that reason," says Alan Hay, director of the WHO influenza collaborating centre at the National Institute for Medical Research in London. Hay's team, and virologists at the US Centers for Disease Control and Prevention (CDC) in Atlanta, are now studying samples of the virus taken from the Hong Kong patient. "We don't know the ins and outs of this yet," says Hay. "It's at quite a preliminary stage."
Previous small outbreaks of swine influenza viruses in people caused what Alan Kendal of Emory University in Atlanta calls "false alarms". In 1986, a Dutch man suffered severe pneumonia after contracting a swine-type virus. And in 1977 a similar virus turned up in a handful of people in Fort Dix, New Jersey.