Climate change futures: health, ecological and economic dimensions

BIODIVERSITY
BUFFERS AGAINST
THE SPREAD OF
INFECTIOUS DISEASE
Figure 2.12
CARBON DIOXIDE
AND AEROALLERGENS
Christine A. Rogers
BACKGROUND
48 | INFECTIOUS AND RESPIRATORY DISEASES
CASE STUDIES
White tailed mouse that can transport Lyme-infected ticks, bacteria
and viruses.
Image: John Good
Diversity of species and mosaics of habitat can help
dampen the impacts of climate change that influence
the colonization and spread of pests and infectious
agents (Chivian 2001; Chivian 2002). Work at the
Institute of Ecosystem Studies in New York State
(LoGiudice et al. 2003) found that voles, squirrels and
chipmunks — competitors of mice — are less susceptible
to carrying the bacteria. Thus, greater biological
diversity among rodent populations appears to “dilute”
rates of infection and thereby reduce transmission.
Quantity of habitat matters. Maintaining extensive
habitat that supports breeding populations of predators
of rodents — for example, raptors, snakes and coyotes
— is essential to keep in check populations of opportunists
and “generalists” (those with wide-ranging diets,
like most rodents), thereby controlling the prevalence of
Lyme and other rodent-related diseases.
Preserving an abundance of animals and multiple
groups performing similar functions, such as predation,
is important for maintaining resilience (Lovejoy and
Hannah 2005). A diversified portfolio of “insurance”
species provides backup if some groups decline due to
habitat change, greater climate variability or disease.
Another dimension of the protective role of biodiversity
is found in the western US, where the blood of the
Western fence lizard contains a chemical that destroys
the causative bacteria, B. burgdorferi, for Lyme. This
may help explain the low incidence of Lyme disease in
the western US.
– P.E.
Allergic diseases are the sixth leading cause of chronic
illness in the US, affecting roughly 17% of the population.
Approximately 40 million Americans suffer from
allergic rhinitis (hay fever), largely in response to common
aeroallergens. In addition, the Centers for
Disease Control and Prevention (CDC) estimate asthma
prevalence in the US at about 9 million children and
16 million adults (or 7.5% of the US population; CDC
2004). Both conditions taken together represent a significant
population of adults and children suffering from
chronic pulmonary symptoms. The self-reported prevalence
of asthma increased 75% from 1980-1994 in
both adults and children. However, the largest
increase — 160% — occurred in preschool-aged children
(Mannino et al. 1998). Low-income families and
African Americans are disproportionately affected by
increases in prevalence, morbidity and mortality (CDC
2004). While some recent reports suggest that these
increases may be leveling off (or decreasing) (Hertzen
and Haahtela 2005; Lawson and Senthilselvan 2005;
Zollner et al. 2005), currently there is a much greater
proportion of the population that is vulnerable to allergen
exposure than ever before.
Although allergic diseases have a strong genetic component,
the rapid rise in disease occurrence is likely
the result of changing environmental exposures. There
are many factors affecting the development of allergic
diseases, and considerable attention has focused on
the indoor environment (IOM 2000), lifestyle factors
(Platts-Mills 2005), as well as outdoor particle exposures
(Peden 2003). Diesel exhaust particles have
been shown to act synergistically with allergen exposure
to enhance the allergic response (Diaz-Sanchez et
al. 2000; D'Amato et al. 2002). Thus, the combination
of air pollution and allergen exposure may be one
factor behind the epidemic of asthma being observed
in developing and developed nations (Diaz-Sanchez et
al. 2003).