Climate change futures: health, ecological and economic dimensions

The rise in minimum temperature results in the expansion
into higher latitudes, which is explained by the
inverse relationship between tick survival and the
degree of subfreezing temperature exposure (Vandyk et
al. 1996). This trend is clearly shown by the spreading
of suitable area north into Canada. Though I.
scapularis has been collected from a variety of locations
in Canada (Keirans et al. 1996, Scotter 2001),
establishment has only been shown for a limited number
of locations in southern Ontario (Schwartz et al.
1997). Climate change may provide the conditions
necessary to yield reproducing populations of I. scapularis
either by the systematic advancement from south
of the border by movement on mammal hosts or by
introductions via attachment to bird hosts (Klich et
al. 1996).
SPECIFIC RECOMMENDATIONS
Further study of Lyme disease and other tick-borne diseases
is warranted. Tick-borne diseases include
babesiosis (an animal, malaria-like illness), erhlichiosis
(bacterial), Rocky Mountain spotted fever and Q fever
(rickettsial diseases), and especially in Europe, tickborne
encephalitis (a viral disease). The possible role
of ticks is being studied in the investigation of an outbreak
of tularemia (“rabbit fever”) that has persisted on
Martha’s Vineyard, MA (USA) since 2000. A Lyme-like
disease has been reported in the southern US
(Mississippi, South Carolina, Georgia, Florida, and
Texas) that also responds to antibiotics, and the possible
role of other ticks in transmitting Lyme is under
study.
Minimum temperature increase also
results in the extension of suitability
into higher altitudes. Elevation is an
important limiting factor for I. scapularis
populations as it indirectly affects population
establishment through its influence
on the complex interaction
between climate, physical factors and
biota (Schulze et al. 1994). As a result
of increasing temperatures, the model
predicts advancement of suitability into
the southern Appalachian Mountains.
Models that predict disease emergence can be valuable
tools for preparing health professionals and
strengthening public health interventions. Personal protective
measures for high-risk populations can reduce
infection rates. Environmental methods, including hosttargeted
vaccination and larvacides, have shown
promise and have the potential to limit the spread of
Lyme disease.
47 | INFECTIOUS AND RESPIRATORY DISEASES
CCF-II: SURPRISE IMPACTS
Lyme disease is a slowly advancing disease, given its
complex life cycle involving ticks, deer, white-footed
mice and the supporting habitat and food sources for
all these elements. Very warm winters may change the
suitable habitat more rapidly than expectations based
on changes in average temperatures alone. But, due
to the many components of the life cycle, and the twoyear
cycle of the ticks themselves, it is unlikely that this
disease will change its distribution and incidence
abruptly and explosively.
CASE STUDIES