Epidemiology

Approximately 18.7 million cases have been reported across 110 countries between 2011 and 2020, with most of the burden in the Latin American and Caribbean region.[6]

Chikungunya virus was first isolated in Tanzania in 1952.[7] Occasional outbreaks have since occurred in Africa, Asia, and the Indian subcontinent, with the largest outbreak occurring on Réunion Island in the Indian Ocean, where around 35% of the island’s 750,000 inhabitants were infected in 2005 and 2006.[8] Since then, the disease has spread to all continents, reaching the Americas via the Caribbean islands in 2013.[9] Increased mobility of people across countries, adaptation of the virus to a more widespread vector (Aedes albopictus), and climate changes have favored global dissemination of the disease.

Locally-acquired (autochthonous) transmission has been reported in 48 countries and territories in the Americas since the initial outbreak in 2013.[10]

The first locally-acquired case in the US was reported in Miami in June 2014. Between 2014 and 2015, 13 locally-acquired cases were reported in the Continental US (Florida and Texas), with none since then. A total of 81 travel-associated cases were reported in US states in 2022. Autochthonous transmission has also been reported in US territories, predominantly Puerto Rico, but also the US Virgin Islands.[11]​ Due to the spread of the vector mosquito, it is possible an autochthonous outbreak will occur in the US. As US citizens tend to spend less time outdoors and availability of air conditioning is widespread, the epidemics will likely not be as extensive as in other countries.[12] As the disease is becoming more prevalent in the Caribbean and the Americas, it is likely that most travel-related cases in the US will be reported from those regions.

Transmission was reported for the first time in Europe in 2007, with anywhere between 170 and 516 cases/year between 2016 and 2019 (mostly travel-related). In 2020, a low number of cases was reported (only 59) for the 24 EU/EEA countries under surveillance. No autochthonous cases were reported in the EU/EEA in 2020.[13]

In the UK, an average of 100 cases were reported each year between 2015 and 2019, but only 36 cases in 2020 and 17 cases in 2021, presumably due to the great reduction of international travel during the COVID-19 pandemic.[14]

More recently, outbreaks have occurred in Kenya (February 2018), Sudan (October 2018), and Congo (April 2019).[15][16][17]​​ The range of affected countries in the Asia-Pacific region has steadily increased in the last 70 years.[18]

Between 1st January and 4th March 2023 there were 113,447 cases reported in the Americas, a fourfold increase compared with the same period in 2022. CDC and WHO have also reported unprecedented numbers of cases in the Americas in regions that were beyond the historical areas of transmission such as Paraguay, Peru, and Bolivia.[19][20]

It is expected that as climate change progresses, warmer and drier environments will facilitate the expansion of the vectors into areas previously considered too cold to guarantee their survival.[21]

WHO: chikungunya - disease outbreak news Opens in new window

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