Our son was recently bit by a tick while on a day hike through tall grass. We found it on him while showering that evening. He has no symptoms. We are worried about Lyme disease. Can you tell us what we need to know?

The story of Lyme disease places us just inside the civilized frontier of the microscopic world. Even with our long history on this planet, new discoveries about microscopic neighbors continue to be made. In the 1970's it was Legionnaire's disease. In the 1980's it was AIDS. In the 1990's Hantavirus made the headlines.

The story of Lyme disease is particularly interesting for two reasons. One is that it illustrates the power of mothers to affect the health of their children, and two, it's an excellent example of those many situations in our lives which if attended to at an early stage, are very simple to remedy, but if allowed to take root and grow become significant, difficult problems.

Lyme disease was first brought to medical attention in 1975, when two mothers living in Lyme, Connecticut became frustrated by the lack of concern given to the unusual illness spreading through their community on the banks of the Connecticut River. These two women began to clamor for an investigation. One contacted the Connecticut State Health Department, and the other contacted physicians at Yale Medical Center. Their initiative set in motion a massive investigation, which in 1982 culminated in the discovery by Dr. Burgdorfer and colleagues of the causative bacteria. It was named Borrelia burgdorferi. At the outset of the investigation, it was noticed that the incidence of Lyme Disease was 30 times greater on the East Bank of the Connecticut River than on the Western Bank. Interviews with affected children and adults and their neighbors revealed that those who exhibited the illness were much more likely to have a cat, a farm animal, a pet with ticks, or a tick bite in the year preceding the illness. As a result, ticks were identified as a likely mechanism for infection. Then, in 1982, Dr. Burgdorfer found the bacteria on the deer tick known as Ixodes dammini or Ixodes scapularis.

After the initial discovery, Lyme disease has been found in 49 of the 50 United States. It is primarily found on the eastern seaboard (between Maryland and Massachusetts), in the upper midwest (most notably Wisconsin and Minnesota), and in the west (particularly in California, Nevada, Utah, and Oregon). In fact, 7 states (Massachusetts, Rhode Island, Connecticut, New York, New Jersey, Wisconsin, and Minnesota) account for 90% of the cases of Lyme disease in the United States. The East Coast cases are transmitted by bites of the Ixodes scapularis tick, and in the West it is transmitted by the Ixodes pacificus tick. Lyme disease is the most common disease caused by a bite in the United States.

Lyme disease is also common in Europe (particularly in Scandinavian countries and in Central Europe -- especially Germany, Austria, and Switzerland), but is found throughout the world, including in Australia where none of the ticks are known to exist. Humans are not the only ones susceptible to Lyme disease; dogs and horses also get it.

The bacteria live in deer and white-footed mice who do not develop the illness. When the appropriate tick feeds on one of these animals, it may become infected.

When an infected tick lands on someone, the bacteria are injected into the bloodstream through the saliva of the tick or deposited on the skin in tick feces. Thankfully, most ticks are not infected.