The transmission of many infectious diseases can be affected by climatic factors.
- Infective agents and their vector organisms are sensitive to factors such as temperature, surface water, humidity, wind, soil moisture, and changes in forest distribution.
This applies particularly to vector-borne diseases (VBD) like malaria.
It is therefore projected that climate change and altered weather patters would affect the range (both altitude and latitude), intensity, and seasonality of many vector-borne and other infectious diseases.
In general, increased warmth and moisture would enhance transmission of VBDs.
However, it should be noted that any such climate-related redistribution of disease may also entail, perhaps in conjunction with other environmental stresses, some localized reductions in rates of infection.
- In tropical countries, VBDs are a major cause of illness and death.
For the major VBDs, estimates of numbers of people at risk and infected, and of VBD sensitivity to climate are shown in the figure.
While the potential transmission of many of these diseases increase in response to climate change, the capacity to control the diseases will also change.
New or improved vaccination can be expected; some vector species can be constrained by use of pesticides.
Nevertheless, there are uncertainties and risks here, too: for example long term pesticide use breeds resistant strains and kills many predators of pests.
- A warmer climate increases occasions of vector borne tropical diseases.
The figure depicts weeks of potential dengue transmission under current temperature and 2°C and 4 °C warming.
Presence of dengue virus, mosquito vector, and exposed human populations are required for disease transmission.
- Malaria and other vector borne diseases will increase in frequency with higher (nocturnal) temperatures.
Malaria climbs up high altitude areas where it has not previously been a serious threat.
In recent years it has become clear that climate change will have direct and indirect impacts on diseases that are endemic in Africa .
Following the 1997 to 1998 El Niño event, malaria, Rift Valley fever, and cholera outbreaks were recorded in many countries in East Africa .
The meningitis belt in the drier parts of West and Central Africa is expanding to the eastern region of the continent.
These factors are superimposed upon existing weak infrastructure, land-use change, and drug resistance by pathogens such as Plasmodium falciparum and Vibrio cholerae.
Although the principal causes of malaria epidemics in the African highlands still are a subject of debate in the literature, there is increasing evidence that climate change has a significant role (WHO, 1998).
In a highland area of Rwanda , for example, malaria incidence increased by 337% in 1987, and 80% of this variation could be explained by rainfall and temperature (Loevinsohn, 1994).