At the Drop of a Tick: A Corps of Lyme-Disease Fighters Meets Its Match in an Army of Arthropods
Wickelgren, Ingrid, Weiss, Rick, Science News
At the Drop of a Tick
When European physicians came to New Haven, Conn., in 1983 to hear U.S. scientists tell the tale of woe experienced by a large cluster of people living on the East Coast, they recognized the story. It usually begins with a red dot on the skin, encircled by increasingly faint rings. Weeks to years later, the saga continues with episodes of chronic or acute arthritis, neurological problems ranging from a stiff neck to meningitis, and/or cardiac malfunctions. The disease has plagued Europeans for nearly 100 years, but before the U.S. epidemic, no one had linked the seemingly unrelated array of symptoms to a single cause. Not until 1982 did scientists identify the bacterial perpetrator, propelled by the bite of a tick.
There remains no surefire way of diagnosing Lyme disease, with its confusing array of symptoms. Physicians don't know how to treat Lyme-affected people who don't respond to antibiotic therapy. And scientists still do not understand how the invading bacterium causes the disease, how it affects so many organs or why the body's immune system doesn't combat it effectively.
But the most alarming new information concerns the Lyme-carrying tick army that both outnumbers and continues to outwit the scientific community. Evidence now suggests a booming increase in the population of the main Lyme-carrying tick, prevalent in the Northeast and upper Midwest, and its spread into new areas. And scientists are discovering just how deeply the tick's life is embedded in the ecosystem as they identify a variety of animal hosts on which it depends for food. These animals abet the tick's spread and make it harder for scientists to target. In addition, some scientists suggest humans may contract the disease even without a tick bite.
The story stars the microscopic Borrelia burgdorferi, a slender, spiral-shaped bacterium, known as a spirochete, that became famous for its devastating performance in Lyme, Conn., in the 1970s. Primarily spread by deer ticks, B. burgdorferi has infected humans in 43 states as well as in Europe, Asia and Australia. In the United States, only Alaska, Hawaii, Montana, New Mexico, Nebraska, Arizona and Wyoming still remain Lyme-free. "This is the [United States'] biggest insect-borne disease of the half-century," says entomologist Durland Fish of New York Medical College in Armonk.
Reported cases of Lyme have increased 10-fold in the United States over the last six years, says epidemiologist Theodore F. Tsai of the Centers for Disease Control's Division of Vector Borne Viral Diseases in Fort Collins, Colo. Last year, 5,000 cases joined the growing U.S. total that now hovers around 13,000. But experts agree that Lyme is both underreported and underdiagnosed. If it follows the pattern of many infectious diseases, Tsai says, the actual total probably numbers four times higher.
At present, 90 percent of the U.S. Lyme cases occur in eight states: California, Connecticut, Massachusetts, Minnesota, New Jersey, New York, Rhode Island and Wisconsin. But the disease is spreading because the tick responsible for most of the U.S. cases is spreading. By systematically examining deer, Fish and his co-workers recently discovered the deer tick in Pennsylvania, Maryland, western Massachusetts, upstate New York and new areas of the Midwest.
The recent tick proliferation remains a mystery, but it probably has had something to do with the replacement of farmland by forests in the Northeast, Fish says. Forests support deer, which have been rapidly increasing in numbers since the turn of the century, and deer support ticks. "We know that deer are essential in maintaining large populations of [this] tick," Fish says.
The human side of the Lyme story in the United States began in the mid-1960s, when Polly Murray, a woman living in the town of Lyme, began to suffer periodic episodes of a flu-like illness, rashes, arthritis and neurological problems such as severe headaches and a stiff neck. …