Parasites and Global Change: Past Patterns, Future Projections

Throughout history, environmental disturbances and global climate change have strongly influenced how humans are affected by parasites, according to parasitologist Eric P. Hoberg. He works at the Agricultural Research Service (ARS) Animal 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 their parasites.

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 productivity.

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 Journal of Biogeography.

ARS is a scientific research agency of the U.S. Department of Agriculture.