Rather than being transmitted directly from human to human, these diseases are transmitted by insects or other vectors. The IPCC concluded that In general, increased warmth and moisture would enhance transmission of these diseases. Malaria is a central example. About 300 million new cases of malaria occur each year. Temperatures above 64 F are required for the parasite to be actively infectious.
Warmer temperature speed up the lifecycle of the parasite and increase infectiousness.
Although this quantitative result must be viewed cautiously, and does not account for the potential for public health measures to mitigate the impact, it clearly indicates the magnitude of the potential impact of climate change on public health. Other types of infectious disease could also increase due to climate change. Warmer temperatures and increased flooding, for example, could increase contamination of drinking water, leading to diarrheal and dysentery epidemics. Cholera, in particular, can survive in sea water when sheltered beneath the mucous outer coat of various algae and zooplankton. Increases in coastal algal blooms, which would be promoted by warming, could therefore amplify cholera proliferation and transmission.