The first-ever maps of global vulnerability to dengue, a mosquito-borne tropical virus that produces a painful condition of body joints sometimes referred to as "breakbone fever," were published by UN University's Canadian-based Institute for Water, Environment and Health. The maps colourfully illustrate the dynamic expansion and contraction of dengue vulnerability worldwide through the year, revealing hotspots in January, April, July and October. While not all vulnerable regions identified currently experience endemic dengue, these maps demonstrate where the virus could become a danger. The work illustrates the consistent exposure to the virus in equatorial regions with greater seasonal trends in sub-tropical latitudes. As the planet warms, according to the paper, conditions in West and Central Africa are particularly favourable for expansion of dengue illness and both regions are urged to plan for this anticipated health challenge. As well, people living in large parts of Europe and mountainous regions of South America - too cold today to sustain mosquito populations year-round - face a "serious threat" of potential dengue virus exposure, the paper warns.