The world is full of nasty viruses, but the one that causes hepatitis c is particularly tricky. Medical science recognised decades ago that not all cases of hepatitis were caused by the two viruses (A and B) that had already been identified. But hepatitis C virus (HCV), which is spread mainly by contaminated blood from, for example, shared syringes, was not isolated and identified until 1989. In 1999, the most recent year for which global figures are available, HCV was believed to have infected some 170m people (see chart). Another 3m join their ranks every year. Fewer than a fifth of those who catch the virus shake it off. In most cases it settles down to form a chronic infection of the liver which, over the course of several decades, can lead to severe forms of liver damage such as cirrhosis and fibrosis, as well as cancer. According to the World Health Organisation (WHO), hepatitis c kills around 500,000 people a year. It is less deadly than AIDS, which claims more than 3m lives annually. However, its higher prevalence (at the moment, some 42m people are infected with HIV, the virus that causes AIDS), longer incubation period, and the absence of effective drugs, mean that it is potentially a more lethal epidemic.
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