Aside from malaria and dengue fever, there’s a plethora of lesser-known diseases transmitted by mosquitoes. These include the o’nyong’nyong virus in East Africa, the Ross River virus endemic to Australia, and the rapidly spreading chikungunya virus. Like dengue, these viruses cause fever, headache and severe joint pain, and there’s no vaccine or treatment. Here, a transmission electron micrograph depicts numerous chikungunya virus particles, composed of a central core surrounded by a viral envelope. Scientists now believe that a single mutation in a viral envelope gene enabled the Asian tiger mosquito to transmit chikungunya to humans. Before 2006, only the yellow fever mosquito could pass on the disease. This has resulted in a surge of outbreaks in non-endemic areas, including one in northeastern Italy in 2007. And the first case of chikungunya-carrying mosquitoes in the United States was recorded this month.