Letting in Lyme Disease

Forest fragmentation—when forests are cut down in such a way that only small parcels are left intact—leads to a higher incidence of Lyme disease according to a study published in the journal Conservation Biology. The white-footed mouse is one of the prime carriers of Lyme disease. These mice are most often found in small forested areas common in the urban landscape where natural predators are absent. Blacklegged ticks feed off the mice and pick up the bacterium that causes Lyme disease. More than 24,000 cases of Lyme disease were reported to the Centers for Disease Control and Prevention in 2011.

There are more mice in fragmented forests due to a lack of predators, and the mice are one of the few animals for the ticks to feed on. Researchers found the risk of Lyme disease increased by a factor of four or five when the land was fragmented to below about three acres in size. In large swaths of forest where more species flourish, ticks have other animals to feed on that do not carry Lyme disease

Like Lyme disease, West Nile virus spreads at higher rates to humans in areas of low biodiversity.

“Our results suggest that efforts to reduce the risk of Lyme disease should be directed toward decreasing fragmentation of deciduous forests of the northeastern United States, particularly in areas with a high incidence of Lyme disease,” Bard College researcher Felicia Keesing told the National Science Foundation. “The creation of forest fragments smaller than five acres should especially be avoided.”