ASM The activity of Chikungunya virus (CHIKV), a mosquito-borne RNA virus that causes fever and joint pain (among other symptoms), increased worldwide in 2025, with cases reported from 40 countries in the Americas, Africa, Asia and Europe. The majority of the cases have been reported from the Americas, with Brazil experiencing the greatest impact. The Centers for Disease Control and Prevention (CDC) has issued Level 2 Travel Health Notices, recommending enhanced precautions for travelers planning to visit certain regions experiencing outbreaks, including China, the Region of the Indian Ocean and Cuba. Additionally, in July 2025, the World Health Organization issued an urgent call for action to prevent CHIKV transmission, citing concerns that early warning signs had been detected, resembling what had been seen 2 decades ago, when a large outbreak occurred in the Indian Ocean in 2005-2006 and then spread globally, with millions of clinically suspected cases.
To decrease transmission, prevent cases and respond to outbreaks, it is important to understand the complexity of mosquito-borne disease maintenance cycles and the numerous factors that can drive emergence and facilitate increased transmission, including climate change, vector movement, viral adaptation and global travel.