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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