This column originally appeared in the August 19, 2007 issue of the Poughkeepsie Journal.

Hudson Valley residents are susceptible to several diseases that normally occur only in wildlife. Lyme disease is the most familiar; others include West Nile virus, anaplasmosis (formerly called ehrlichiosis), and babesiosis. Twenty-five years ago, these diseases were absent from our landscape. Now they are established and spreading. Research has found that when humans modify the environment— fragmenting habitat and reducing species diversity— our probability of contracting these diseases increases.

On a summer day in 1999, West Nile Virus quietly entered New York City. It hitchhiked from the Mediterranean region in the bloodstream of a tourist or an illegally transported bird. After arriving in the U.S., the infected bird or tourist was bitten by local mosquitoes. These mosquitoes then carried the virus to local birds, where it was able to replicate and persist. Within five years, West Nile Virus had spread to California.

Increased West Nile virus infection has been linked to two environmental causes. The first is low bird diversity. West Nile virus thrives best in birds like blue jays, grackles, and house sparrows. These species are abundant in disturbed ecosystems, including urban and suburban areas in the Hudson Valley. Natural ecosystems have more diverse bird communities, including species that are not good hosts for the virus. As a result, mosquitoes and humans living in pristine areas are less likely to be infected.

Wetland loss is also tied to increased West Nile virus infection. Wetland ecosystems harbor mosquito populations, but they are also home to an array of bird species. Larger wetlands have higher bird diversity and a lower incidence of infected mosquitoes.

In the Hudson Valley, Lyme disease is much more common than West Nile virus— with Dutchess County having one of the highest infection rates in the nation. Research at the Institute of Ecosystem Studies has shown a link between forest loss and Lyme disease risk. When a large forest is reduced to smaller fragments, mammal diversity declines. The mammals that persist in these forest pockets, such as white-footed mice and chipmunks, are the species that most readily transmit Lyme disease bacteria to ticks.

As a society, we need to manage ecosystems in a way that reduces disease risk. In the case of Lyme disease and West Nile virus, this means protecting large tracts of forests and wetlands. By minimizing fragmentation we will protect species diversity, because large ecosystems support a greater number of species.

Urban and suburban sprawl often result in forest and wetland fragmentation, but commercial and residential dwellings can be designed in a way that minimizes habitat loss. For example, biodiversity can be preserved if buildings are clustered to protect large tracts of undisturbed land. In areas like the Hudson Valley, where natural areas are being converted into residences, concentrating development to minimize fragmentation will be an important tool in mitigating disease risk.

Given the strong link between biodiversity loss and disease, we need to protect and strengthen national policies aimed at preserving biodiversity. The past several years have seen a push to weaken the effectiveness of The Endangered Species Act. National-level politics have attempted to thwart species recovery plans, censure scientific research documents, and create a bottleneck that makes it nearly impossible to get animals and plants listed for protection. Over 268 species are awaiting review, and many of the 58 species officially listed during the past six years required a court-order to do so.

We all depend on the health protection that intact ecosystems provide; biodiversity is a critical part of this picture. When we protect a species we are also protecting ourselves.

Dr. Richard Ostfeld is an Animal Ecologist at the Institute of Ecosystem Studies in Millbrook, NY.