Scientists study possible link between tree deaths, Lyme disease

SANTA CRUZ, Calif. (MCT) — Over the past 15 years, an invasive plant disease has left a patchwork of dead and dying trees in California's majestic coastal forests. But the loss of trees is changing more than just panoramic views: The number of ticks that can carry a disease that causes painful joint swelling, fatigue and even neurological damage is growing — a result of the gaps created in the forest when trees die, a recent study found.

To determine how the loss of trees affects ticks, their hosts and the Lyme disease they might carry, researchers at UC Berkeley, UC Santa Barbara and the Cary Institute of Ecosystem Studies in New York have embarked on a multi-year study of animal populations in a North San Francisco Bay forest infected with Sudden Oak Death.

"We know that Sudden Oak Death is infecting and killing a number of tree species all along coastal woodlands in California," said Andrea Swei, postdoctoral researcher at UC Berkeley and lead author of the study.

Swei said the effects of invasive species are unpredictable, complicated and can have ecological consequences that might at first glance seem totally unrelated, including changes in the risk to humans of contracting certain diseases.

Sudden Oak Death was first reported in 1995 in Marin County and is now found in coastal counties ranging from Monterey to Humboldt, including the forests of Big Sur and the Santa Cruz Mountains. Tanoaks, live oaks and California black oaks are all susceptible to the disease, which is caused by a microbe related to the potato blight that caused the Irish famine of the 1840s.

In addition to being harder hit by the devastating plant disease, humid northern coastal counties are also plagued by the states' largest risk of Lyme disease, according to Anne Kjemtrup, an epidemiologist with the state Department of Public Health.

Lyme disease is mostly spread by the not-quite-adult — or "nymphal" — stage of the tick, and these poppy seed-sized arachnids fare better in wet areas such as the Northern California Coast. Last year, 7.6 cases of Lyme disease were reported for every 100,000 people in Mendocino County and 6.5 per 100,000 people in Del Norte County, a rate 20 times greater than the state average. Lyme disease was first detected in the 1970s in Connecticut, and although it is often considered an East Coast affliction, it has been found in every state except Hawaii, according to the U.S. Centers for Disease Control and Prevention. The disease has been found in nearly all of California's 58 counties. In the Forest of Nisene Marks State Park in Aptos, nearly one in five ticks tested positive for the disease in 2000 and 2001, San Jose State University researchers found.