Vector-Borne Disease and Climate Geography

Vector-borne diseases — those transmitted to humans not by direct contact but by an intermediate organism, or vector, such as a mosquito, tick, flea, or sandfly — depend fundamentally on the vector's own ecological requirements, which are themselves governed by temperature, humidity, rainfall, and land cover. Malaria, caused by Plasmodium parasites transmitted by female Anopheles mosquitoes, requires temperatures generally above about 16–18°C for the parasite to complete its development within the mosquito (a threshold formalized in the concept of the extrinsic incubation period), which is why the disease has historically been confined largely to tropical and subtropical latitudes; the WHO's World Malaria Report estimated roughly 249 million malaria cases and 608,000 deaths worldwide in 2022, with sub-Saharan Africa accounting for about 94 percent of both figures. Dengue fever, transmitted by Aedes aegypti and Aedes albopictus mosquitoes, has a similarly climate-bounded distribution but has expanded markedly in recent decades: the WHO reported that the global incidence of dengue increased roughly eightfold between 2000 and 2019, with the disease now endemic in more than 100 countries, a spread epidemiologists attribute to a combination of unplanned urbanization, increased international travel, and a warming climate that extends the mosquito's viable range and active season.