11.2.5.2. Vector-Borne Diseases

Health impacts secondary to the impacts of climate change on ecological and social systems should include changes in the occurrence of vector-borne infectious diseases in temperate and tropical Asia (see Chapter 9). The distribution of diseases such as malaria is influenced by the spread of vectors and the climate dependence of infectious pathogens (Hales et al., 1996; McMichael et al., 1996; Epstein et al., 1998). In recent years, the resistance of anopheline mosquito to pesticides and of malaria parasites to chloroquine has affected eradication activities (Trigg and Kondrachina, 1998). Malaria still is one of the most important diseases in countries in tropical Asia such as India (Bouma et al., 1994; Akhtar and McMichael, 1996; Mukhopadhyay et al., 1997), Bangladesh, Sri Lanka (Bouma and Van der Kaay, 1996; Gunawardena et al., 1998), Myanmar, Thailand, Malaysia (Rahman et al., 1997), Cambodia, Laos, Vietnam (Hien et al., 1997), Indonesia (Fryauff et al., 1997), Papua New Guinea (Genton et al., 1998), and Yunnan, China (Jiao et al., 1997; Xu and Liu, 1997) as a result of the presence of the mosquito vectors and the lack of effective control.

With a rise in surface temperature and changes in rainfall patterns, the distribution of vectors such as mosquito species may change (Patz and Martens, 1996; Reiter, 1998). Changes in environmental temperature and precipitation could expand vector-borne diseases into temperate and arid Asia. The spread of vector-borne diseases into more northern latitudes may pose a serious threat to human health. Climate change is likely to have principal impacts on epidemics of malaria, dengue, and other vector-borne diseases in Asia (Martens et al., 1999). The epidemic areas of vector-borne diseases in Asia would depend on many demographic and societal factors, as well as environmental hygiene for vector control, available health infrastructure, and medical facilities (see also Chapter 9).

11.2.5.3. Diseases Resulting from Higher UV-B Exposures

Depletion of stratospheric ozone that normally filters out ultraviolet radiation in sunlight in the region from 280 to 320 nm (the UV-B region) has been linked to widespread use of volatile halogenated organic compounds, particularly chlorinated and brominated methanes and chlorofluorocarbons. Some of these compounds also are effective GHGs and therefore contribute to global warming as well. The quantitative relationship between UV-B dose and its physiological effect varies with the wavelength of UV-B exposure (Ilyas et al., 1999). These effects include melanoma and non-melanoma skin cancers, cataracts and other ocular diseases, and dysfunction of the systemic and cutaneous immune systems (Kripke, 1994). The known effects of UV-B on the eye include inflammatory reactions from acute exposure, snow blindness (photo-kerato-conjunctivitis), and long-term damage to the cornea and lens (cataracts) from chronic exposure. It has been demonstrated that damage to melanocytes in human skin initiates the progression of changes leading to melanoma skin cancer (Kripke, 1994). Suppression of the immune response by UV-B radiation involves damage to Langerhans cells and subsequent activation of T-lymphocytes, thus increasing the severity of certain infectious diseases.

The impacts of greater exposure to shorter wavelength UV radiation on human health are cumulative and, for some effects, may have long latencies. Noticeable increases in UV-B radiation over high and mid-latitudes as a result of depletion of stratospheric ozone have occurred in recent decades (Mckenzie et al., 1999; WMO, 1999; ACIA, 2000). Climate change could make conditions for the spread of diseases associated with higher UV-B doses more favorable.

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