Knocking out the source (Image: Jorge Saenz/AP/PA)

DENGUE fever has re-entered the US via the Florida Keys after an absence of 65 years.

The mosquito-borne virus has been identified in 28 people from Key West by the US Centers for Disease Control. The CDC announced the findings last week in its Morbidity and Mortality Weekly Report.

“We don’t know for sure that this hasn’t happened before without being noticed,” says Christopher Gregory of the CDC’s dengue branch in San Juan, Puerto Rico. “It could be the tip of the iceberg.”

Most cases resolve after flu-like symptoms, says Gregory. He …