Often called the "great imitator," Lyme disease can be tricky to recognize by people who have it because its symptoms can mimic those of mononucleosis, meningitis, multiple sclerosis or rheumatoid arthritis and other diseases. In fact, when the disease was first observed in children in Old Lyme, Conn., in 1975, doctors suspected an outbreak of juvenile rheumatoid arthritis.

However, rheumatologists from Yale discovered that a tick was at fault. It wasn't until years later that a researcher identified the real culprit behind the children's swollen knees and fevers: a spiral shaped bacterium called Borrelia burgdorferi, which is transmitted by the tiny deer tick.

Today, cases of Lyme disease have been identified in nearly all 50 states, but the vast majority of breakouts occurs in the Northeast, as well as in Wisconsin and Minnesota. And while the symptoms of Lyme disease can mimic other conditions, it can be diagnosed and treated fairly easily by a doctor who recognizes the signs.

Lyme typically occurs in the following stages:

This stage occurs during the first seven to 10 days after infection. It is characterized by an expanding red rash (sometimes in the shape of a bull's eye) and viral-like symptoms including chills, fever, headache, stiff neck, fatigue, swollen lymph nodes, and aching joints and muscles.

The bull's eye rash surrounds the bite site, which is generally found on or near the belt line, thigh, groin, trunk or armpits, as ticks are attracted to warm, moist regions of the body. About two-thirds of patients don't recall the tick bite, which is painless, although the site may burn, itch or hurt.

After several weeks or months of infection, additional symptoms may include irregular heartbeat, numbness or severe fatigue. This stage may also include nervous system problems such as severe headaches, temporary facial paralysis (especially Bell's Palsy) or poor motor coordination. These symptoms may develop weeks to months after skin lesions disappear.

This stage can occur anywhere from months to years after the initial infection. At this point, arthritis pain and swelling may occur in a few large joints. The most common joint to be affected by arthritis is the knee. Arthritis is most often temporary, but about 10 percent of people affected with Lyme disease will develop chronic Lyme arthritis if untreated. Neurological disorders can also occur at this stage. (One type of condition known as tertiary neuroborrelias can result in confusion, forgetfulness and poor thinking.) Some patients may develop numbness or tingling in some areas of the body.

Lyme disease is generally diagnosed by the presence of the signs and symptoms in the earlier stages, especially the expanding red rash. A blood test, which detects antibodies directed against the bacterium that causes Lyme disease, may help confirm the diagnosis.

Early diagnosis and treatment are important - Lyme disease is curable if treated early enough. It can be treated with antibiotics at any stage, but the earlier treatment begins, the better the chance of preventing its progression to a later stage. Adults are generally given antibiotics such as doxycycline or amoxicillin orally for several weeks during the early stages of the disease. Typically intravenous therapy is given for neurologic disease, severe heart disease and arthritis that hasn't responded to oral therapy.

In recent years, researchers have developed two vaccines, LYMErix and ImuLyme. LYMErix, which has been approved by the Food and Drug Administration, must be taken in three shots over a full year to build immunity, and it is limited to people from 15 to 70 years old. The vaccine is not yet approved for people with joint problems such as rheumatoid arthritis (simply because no tests have been done in such patients). There is, however, no evidence that the vaccine would be harmful for people with joint problems.

Furthermore, the vaccine does not prevent other infections carried by ticks and is not yet approved for children, although approval is expected within a year or two. For these reasons experts recommend you take other precautions when outdoors such as: