Many waterborne and vectorborne infectious diseases are strongly influenced by climate conditions, and several are common within cities. The clearest example is dengue, the most important vectorborne virus globally. Dengue transmission has increased dramatically in tropical developing regions in the past few decades due to the weakening of vertical control programs in many regions, coupled with rapid unplanned urbanization, producing breeding sites for
Aedes mosquitoes, and high human population densities, supplying a large pool of susceptible individuals.
25 Increasing travel has helped to spread the four different serotypes of dengue around the world, heightening exposure to multiple strains, which in turn increases the severity of clinical disease. In addition, the distributions of
Aedes and dengue are favored by high absolute humidity, which increases with high temperatures and rainfall.
26,
27 Climate change is therefore projected to cause important increases in dengue endemic areas both at the global level
28 and within certain developing regions, including China.
29 Again, socioeconomic development, improving housing,
30 and appropriate control interventions
31 can help to counter these trends but may not offer complete protection particularly if control programs are not sustained over time. Singapore is one of the richest countries in the world; yet, dengue is reemerging there,
32 with almost half of local adults surveyed showing evidence of previous infection.
33 More speculatively, global environmental changes may favor the emergence of new infectious diseases,
34,
35 which may spread faster within and between cities due to travel links and higher rates of person-to-person contact.