9.6.2. Aeroallergens (e.g., Pollen)
Daily, seasonal, and interannual variation in the abundance of many aeroallergens,
particularly pollen, is associated with meteorological factors (Emberlin, 1994,
1997; Spieksma et al., 1995; Celenza et al., 1996). The start of the grass pollen
season can vary between years by several weeks according to the weather in the
spring and early summer. Pollen abundance, however, is more strongly associated
with land-use change and farming practices than with weather (Emberlin, 1994).
Pollen counts from birch trees (the main cause of seasonal allergies in northern
Europe) have been shown to increase with increasing seasonal temperatures (Emberlin,
1997; Ahlholm et al., 1998). In a study of Japanese cedar pollen, there also
was a significant increase in total pollen count in years in which summer temperatures
had risen (Takahashi et al., 1996). However, the relationship between meteorological
variables and specific pollen counts can vary from year to year (Glassheim et al., 1995). Climate change may affect the length of the allergy season. In addition,
the effect of higher ambient levels of CO2 may affect pollen production.
Experimental research has shown that a doubling in CO2 levels, from
about 300 to 600 ppm, induces an approximately four-fold increase in the production
of ragweed pollen (Ziska and Caulfield, 2000a,b).
High pollen levels have been associated with acute asthma epidemics, often
in combination with thunderstorms (Hajat et al., 1997; Newson et al., 1998).
Studies show that the effects of weather and aeroallergens on asthma symptoms
are small (Epton et al., 1997). Other assessments have found no evidence that
the effects of air pollutants and airborne pollens interact to exacerbate asthma
(Guntzel et al., 1996; Stieb et al., 1996; Anderson et al., 1998; Hajat et al.,
1999). Airborne pollen allergen can exist in subpollen sizes; therefore, specific
pollen/ asthma relationships may not be the best approach to assessing the risk
(Beggs, 1998). One study in Mexico suggests that altitude may affect the development
of asthma (Vargas et al., 1999). Sources of indoor allergens that are climate-sensitive
include the house dust mite, molds, and cockroaches (Beggs and Curson, 1995).
Because the causation of initiation and exacerbation of asthma is complex, it
is not clear how climate change would affect this disease. Further research
into general allergies (including seasonal and geographic distribution) is required.
| Table 9-1: Main vector-borne diseases: populations
at risk and burden of disease (WHO data). |
 |
| Disease |
Vector
|
Population
at Risk
|
Number of
People Currently
Infected or New
Cases per Year
|
Disability-
Adjusted
Life Years Losta
|
Present
Distribution
|
| |
| Malaria |
Mosquito
|
2400 million
(40% world population)
|
272,925,000
|
39,300,000
|
Tropics/subtropics
|
| |
|
|
|
|
|
| Schistosomiasis |
Water Snail
|
500-600 million
|
120 million
|
1,700,000
|
Tropics/subtropics
|
| |
|
|
|
|
|
| Lymphatic filariasis |
Mosquito
|
1,000 million
|
120 million
|
4,700,000
|
Tropics/subtropics
|
| |
|
|
|
|
|
African trypanosomiasis
(sleeping sickness) |
Tsetse Fly
|
55 million
|
300,000-500,000
cases yr-1
|
1,200,000
|
Tropical Africa
|
| |
|
|
|
|
|
| Leishmaniasis |
Sandfly
|
350 million
|
1.5-2 million
new cases yr-1
|
1,700,000
|
Asia/Africa/
southern Europe/
Americas
|
| |
|
|
|
|
|
Onchocerciasis
(river blindness) |
Black Fly
|
120 million
|
18 million
|
1,100,000
|
Africa/Latin America/
Yemen
|
| |
|
|
|
|
|
| American trypanosomiasis (Chagas'disease) |
Triatomine Bug
|
100 million
|
16-18 million
|
600,000
|
Central and
South America
|
| |
|
|
|
|
|
| Dengue |
Mosquito
|
3,000 million
|
Tens of millions
cases yr-1
|
1,800,000b
|
All tropical countries
|
| |
|
|
|
|
|
| Yellow fever |
Mosquito
|
468 million
in Africa
|
200,000
cases yr-1
|
Not available
|
Tropical South
America and Africa
|
| |
|
|
|
|
|
| Japanese encephalitis |
Mosquito
|
300 million
|
50,000
cases yr-1
|
500,000
|
Asia
|
| |
