Chikungunya fever is a viral disease transmitted to humans by the bite of infected mosquitoes. It causes an acute illness, typically featuring fever, headache, nausea, rash and severe joint pain, but is usually not fatal. In some cases joint pain may persist for months, or even years.  Its name comes from a local African language and means "to become contorted," referring to the stooped appearance of sufferers with joint pain.  There is no specific treatment; medical care is aimed at relieving symptoms.
The disease was first reported from Tanzania in 1952 and subsequently spread to sub-Saharan Africa, South East Asia and the Pacific, causing large epidemics.  In Africa, the natural cycle of the virus is between wild non-human primates and forest-dwelling Aedes mosquitoes.  However, once humans became infected, they formed a new disease reservoir. In many regions, chikungunya is now maintained in a mosquito-human-mosquito cycle.
The disease is usually transmitted by Aedes aegypti mosquitoes. More recently, chikungunya has also been associated with a new vector, Aedes albopictus, which has spread from Asia to tropical areas worldwide.
Recent years have witnessed several large chikungunya outbreaks in different parts of the world, including Democratic Republic of Congo (1999/2000), India (2006/2007) and Gabon (2007).  From 2005 to 2007, a major outbreak occurred in the islands of the Indian Ocean, including Mauritius, Mayotte, Madagascar and Reunion. The outbreak in Reunion was especially severe, with one-third of the population infected and at least 200 deaths associated with the virus.
In 2007, outbreaks spread to several South East Asian countries, including Singapore, and to European countries for the first time.  In Italy there were more than 200 laboratory confirmed cases.  Officials believe the virus was introduced into Italy when an Indian tourist arrived infected with the virus. The virus was spread by the Asian tiger mosquito, Aedes albopictus, which had reached Italy nearly two decades earlier.  This was the first time the virus demonstrated that it could strike a ‘first-world’ country.
When the chikungunya virus arrives in areas where there is no immunity in the population, outbreaks can be especially severe.  Countries with susceptible populations and effective mosquito vectors, that receive large numbers of visitors from epidemic areas, are vulnerable to chikungunya outbreaks.  Countries in the Americas are considered to be particularly at risk from this emerging disease because of the presence of the two main disease vectors, Aedes aegypti and Aedes albopictus.