Scientists are warning of a possible chocolate shortage as disease ravages cocoa crops across the world. Some of the world's largest chocolate-producing countries, such as the Ivory Coast, could lose a third of their crop this year, because of the problem. One disease, the cacao swollen shoot virus (CSSV), which can kill the trees, is affecting crops in west Africa. Around 70 per cent of the world's chocolate comes from west Africa. In Brazil, another major producer of chocolate, crops are being affected by a fungus called witches' broom. Research has uncovered cacao varieties in Africa which are partially resistant to the disease and scientists are trying to breed more hardy versions.