Chikungunya: out of the tropical forests and heading our way …

Chikungunya is caused by an alphavirus, which was originally confined to mammals and non-human primates inhabiting the forests of tropical Africa and only occasionally affected humans. However, over the past 12 years there has been an explosion of reports of chikungunya disease, which began its spread from coastal Kenya in 2004 through the islands of the Indian Ocean and into India and South-East Asia, moving through Indonesia and southern China, and finally reaching Polynesia. Just over 2 years ago a new epidemic started in the Caribbean islands, from where it is moving rapidly through central and South America, leading to over a million new infections within a year. These two epidemics were caused by distinct strains of the chikungunya virus (CHIKV). Chikungunya infection is characterised by high fever and severe pain and swelling in the joints, which can lead to chronic and disabling arthritis in a substantial proportion of infected people. What has led to the rapid spread of this debilitating infection throughout the world?