CIESIN Thematic Guides

Changes in the Incidence of Vector-borne Diseases Attributable to Climate Change

A vector-borne disease is one in which the pathogenic microorganism is transmitted from an infected individual to another individual by an arthropod or other agent, sometimes with other animals serving as intermediary hosts. The transmission depends upon the attributes and requirements of at least three different living organisms: the pathologic agent, either a virus, protozoa, bacteria, or helminth (worm); the vector, which are commonly arthropods such as ticks or mosquitoes; and the human host. In addition, intermediary hosts such as domesticated and/or wild animals often serve as a reservoir for the pathogen until susceptible human populations are exposed.

Nearly half of the world's population is infected by vector-borne diseases, resulting in high morbidity and mortality. The distribution of the incidence of vector-borne diseases is grossly disproportionate, with the overwhelming impact in developing countries located in tropical and subtropical areas. The Summary of Key Vector-borne Diseases provides a brief description of the manifestation, causative agent, vector species, host, prevalence, population at risk, present geographic distribution, and possible change in distribution due to climate change of key vector-borne diseases (CIESIN 1994).

Weather affects vector population dynamics and disease transmission, with temperature and humidity considered key variables. Only recently have researchers attempted to predict how climate change might affect the distribution of vector-borne diseases. A comprehensive model should consider both the direct impacts (such as changes in temperature or rainfall) and indirect impacts (such as changes in hydrology or agriculture) of global warming on the agent, vector, intermediary host, and the human host. The response of each element of the disease process to climate change may have ramifications for the others.

To better understand the potential impact of changes in the incidence of vector-borne diseases attributable to climate change requires examination of the following topics: