Between Jan. 9 and 15, five people in Cambodia contracted bird flu, and four died of it within a few days -- four young girls and a 35-year-old man. Only the first case, an eight-month-old boy, survived.
This might seem like a minor event, but the World Health Organization sent rapid response teams into the country to help the Cambodian ministry of health. They've been looking for more cases and educating local residents about how to avoid the disease -- even though it's one of the hardest diseases to catch.
"Bird flu" is a vague term: all influenzas come from birds, especially domestic poultry, though they sometimes reach us through pigs and other mammals. The Cambodians had H5N1 flu, which first got our attention when it broke out among chickens and humans in Hong Kong in 1997. That outbreak was stopped by killing every chicken and duck in the region, and banning further imports from the mainland.
Six years later human H5N1 returned, in Vietnam, and since then has sputtered away from Indonesia and South Korea to Egypt and Nigeria.
Between 2003 and the end of 2012, the WHO confirmed no more than 610 human H5N1 cases, most of them in Vietnam, Indonesia and Egypt. This, out of a population of over seven billion, makes it one of the world's rarest diseases.
Rare and dangerous
Its rarity is precisely what makes it so dangerous. Because it evolved to infect birds, H5N1 isn't designed to infect mammals. Humans, therefore, are a "naive" population with almost no immunity to it. That was what scared the health authorities in Hong Kong, and it's what scares the WHO today.
Out of those 610 cases, 360 people died. That means the "case fatality rate" (CFR) was 59 per cent. The CFR varies by country -- it's 35 per cent in Egypt, and 83 per cent in Indonesia. But globally, three out of five people who catch H5N1 will die of it within a very few days.