Chikungunya virus seems, at first, to have a lot in common with dengue virus, another mosquito-borne pathogen. Both cause extremely painful diseases—chikungunya’s name comes from a Makonde word meaning “that which bends up,” referring to the contortions sufferers put themselves through due to intense joint pain. Dengue’s nickname is breakbone fever. Both viruses are primarily transmitted by the Aedes aegypti mosquito, and both have been moving slowly closer to the United States over the past decades, with local cases of dengue fever already found in Florida and Texas.

Last week the Centers for Disease Control and Prevention announced the first locally acquired cases of chikungunya in the United States. A woman in Miami-Dade County and a man in Palm Beach County, neither of whom had left the country recently, both came down with the dreaded disease.

Read it at Slate.