With an enemy usually no bigger than the head of a pin, it's no wonder growing numbers of Americans living in northern states are losing the war against Lyme disease, the most commonly reported illness transmitted by ticks in the US.
Reported cases are at a record high: Nearly 18,000 people a year are infected, according to the Centers for Disease Control and Prevention, which receives reports on only a minority of cases.
Although the surgeon general's goal stated in Healthy People 2010 is to reduce Lyme-disease cases by 44 percent in states where Lyme-infected deer ticks now reign unchecked (the northeast from Maryland to Massachusetts and in Wisconsin, Minnesota and northern California), prevailing forces seem determined to spell failure.
The deer population is exploding, with nothing more than a short hunting season to curb their numbers. More and more Americans seeking residences and recreation are moving into deer habitat, in suburban and rural wooded areas. And the deer, seeking ever-shrinking natural sources of food, are coming closer and closer to populated areas, brazenly nibbling on landscaped vegetation right outside people's homes.
But while most people who live or work in areas where Lyme disease is prevalent are aware of the illness and its potential complications, no more than half take any of the recommended precautions to protect themselves from a surreptitious bite by a Lyme-carrying tick.
According to Dr. Gregory Poland, a Lyme disease expert and a professor of medicine and infectious diseases at the Mayo Clinic, "All the behavioral measures intended to prevent Lyme disease are incomplete and impractical." Because of that, many people take chances that no Lyme-carrying ticks will bite them or that antibiotics will cure them.
In a report in The Mayo Clinic Proceedings in July 2001, Poland noted that studies had not yet demonstrated that wearing protective clothing made a difference in the risk of developing Lyme disease. And while these and later studies are not the gold standard of research, it is easy to see why the advice falls short of complete or near-complete protection.
The main carrier of Lyme disease is the nymph of a tick ( Ixodes scapularis or Ixodes pacificus ) that is no bigger than the head of a pin and able to crawl unnoticed through the tiniest of openings, establish a resting site on the skin and start feeding on blood without creating the slightest sensation to warn of its presence.
Not until the immature tick has fed for a while and become engorged with blood is it likely to be noticed, even by those who do daily body checks. Seventy percent of people who contract Lyme disease don't recall being bitten.
The Lyme disease bacterium, a spirochete called Borrelia burgdorferi, lives in the midgut of the tick and when a feeding tick spits out the water from its blood meal, it can transfer the bacterium into its host.
"Short of a vaccine, I don't see how we will control this disease or achieve the goal of Healthy People 2010," Poland said in an interview. "What would help in suburban areas is controlling the deer population" through hunting (not popular in residential areas) or birth control.
Small mammals like the white-footed mouse are hosts for immature ticks, and deer are hosts and dispersal systems for adult ticks.
Still, recommended measures intended to reduce exposure to infected ticks and curb ticks' ability to find safe feeding stations on people are worth taking, Poland said.