Parasites and Global Change: Past Patterns, Future
Projections By Ann
Perry October 14, 2008
Throughout history, environmental disturbances and global
climate change have strongly influenced how humans are affected by parasites,
according to parasitologist
Hoberg. He works at the Agricultural
Research Service (ARS)
Parasitic Diseases Laboratory in Beltsville, Md.
Now Hoberg and University of
Toronto zoologist Daniel R. Brooks have formulated a new theory to explain
evolutionary and geographic histories for complex associations of hosts and
During the past 300 million years, a period extending deep into
evolutionary time, repeated episodes of environmental disruption have exerted a
pervasive influence on the distribution of hosts, pathogens and diseases. These
disturbances can limit--or enhance--the ability of a pathogen to move to a new
host or geographic region, and are central to understanding the link between
ecological change and emerging disease.
For instance, tapeworms survived the extinction event that killed the
dinosaurs by "jumping" from their ancient reptilian hosts to seabirds and then
later to marine mammals. During the glacial ages, which ended only 10,000 years
ago, the movement of hosts and parasites shaped present-day faunal
distributions across land and sea.
Hoberg and Brooks suggest that similar evolutionary patterns,
determined by what is known as host switching or geographic colonization, will
continue as environmental perturbation, including global climate change,
becomes more pronounced.
Lessons learned from Earth's history can provide a foundation for
understanding how these complex biological associations will respond as the
climate warms and habitats change. These patterns and associations emphasize
the connection between ecological disturbances and the shifting relationships
between host and the emergence of disease.
Accelerated climate change and the attendant disruption of ecological
continuity will produce global shifts that may well support the emergence and
spread of novel pathogens, parasites and diseases. These potentially dramatic
changes could play important roles in human health and agricultural
Understanding the historical host-parasite systems and interactions
over hundreds of millions of years--including the relatively recent past--are
essential for successfully addressing the challenges that will arise from this
dynamic environmental change.
A paper on this research appears in the September 2008 issue of
ARS is a scientific research agency of the
U.S. Department of Agriculture.