Lyme disease is an infection caused by a spirochete (say “SPY-ROH-KEET” that humans can get from the bite of an infected deer tick. The spirochete's scientific name is Borrelia burgdorferi. Lyme disease is called “The Great Imitator” because its symptoms mimic many other diseases. It can affect any organ of the body, including the brain and nervous system, muscles and joints, and the heart.

People usually get Lyme disease from ticks infected with Lyme spirochetes. Most human cases are caused by the nymphal, or immature, form of the tick. Nymphs are about the size of a poppy seed. Because their bite is painless, many people do not realize they have been bitten.

If you think you might have Lyme Disease, click here to find out what to do.

Ticks may remain attached for several days while they feed. The longer they remain attached, the greater the risk that they will pass the Lyme bacteria into your bloodstream, where they will start spreading throughout your body.

If pregnant women are infected, they sometimes pass Lyme disease to their unborn children. Some doctors believe other types of human-to-human transmission are possible but little is known for certain.

Lyme disease has been found on every continent except Antarctica. It is found all across the United States, with a particularly high incidence in the east, midwest, and west coast. It seems to be spreading.

Not all ticks are infected. Within endemic areas, there is considerable variation locally, depending on type of habitat, presence of wildlife, and other factors. In the south, a Lyme-like disease is called STARI (Southern Rash-Associated Tick Illness).

In addition to the variation that occurs in nature, there is also variation in how aggressively the states have tested ticks for infection. Thus, many times the reported incidence of infected ticks reflects the fact that the state has done little or no testing of ticks in the area. Click here to view maps that show a dramatic increase in the number of states reporting Lyme to the Centers for Disease Control for the years 1985, 1987, and 1992. Some of this increase may be because of disease spread, but it is also likely that it reflects growing public awareness of the disease.

Diagnosis is clinical and is based primarily on recognition of the typical symptoms of Lyme disease in a person who lives in a high-risk area. Doctors like to have hard evidence to back up their opinions, but testing is not an exact science: the tests for Lyme disease may sometimes be negative in cases where disease is actually present, and false positive tests, though less common, are also possible. Therefore, experienced doctors recommend that Lyme disease be diagnosed clinically, meaning they base the diagnosis on an evaluation of your risk and your symptoms.

People with chronic Lyme disease may be misdiagnosed with more familiar conditions with symptoms that mimic Lyme disease.

Since scientists have not figured out the cause of these diseases and treatment does not call for antibiotics, the underlying Lyme infection is allowed to progress unchecked.

Some doctors consider a bull’s-eye rash diagnostic and don’t require further tests. Others, however, require laboratory confirmation before treatment.

Culture is the “gold standard” test for identifying bacteria. A sample of the organism is taken from the patient is allowed to grow in a medium and then identified. Culture is accepted as proof of infection. While culture is used to diagnose many infections, it is not practical for Lyme because the bacteria grow too slowly. There are no commercially available culture tests for Lyme.

The most common tests measure the patient’s antibody response to infection. When your body is invaded by the Lyme spirochetes, your immune system makes antibodies to fight the infection. Tests that measure antibody levels are indirect tests because they measure the body’s response to infection rather than the presence of the bacteria themselves.

During the first 4-6 weeks after exposure, most people have not developed the antibody response that the test measures. Treatment should not be delayed pending a positive test result if the suspicion of Lyme disease is high (exposure, tick bite, possible rash).

Two primary antibody tests are used to diagnose Lyme disease, the ELISA and the western blot. Doctors commonly order an ELISA first to screen for the disease and then confirm the disease with a western blot. However, current ELISA tests are not sensitive enough for screening and may miss over half the true cases. Because of this, the best antibody test to use for diagnosis is the western blot.

The read-out from the western blot looks like a bar code. The pattern produced by running the test with your blood is compared to a template pattern that represents known cases of Lyme disease. If your blot has bands in the right places, and the right number of bands, it is positive. Some of the bands are more significant than others and your doctor may decide you have Lyme disease even if your western blot does not have enough bands or the right bands to be reported to the Centers for Disease Control and Prevention (CDC) for surveillance purposes.

Different laboratories use different methods and criteria, so you can have a positive test result from one lab and a negative test result from another. Lyme disease is known to inhibit the immune system and twenty to thirty percent of patients have falsely negative antibody tests.

Two other tests that may be used to diagnose Lyme disease are PCR and antigen detection tests. Polymerase chain reaction (PCR) multiplies a key portion of DNA from the Lyme bacteria so that it can be detected. While PCR is highly accurate when the Lyme DNA is detected, it produces many false negatives. This is because Lyme bacteria are sparse and may not be in the sample tested. Antigen detection tests look for a unique Lyme protein in fluid (e.g. blood, urine, joint fluid). Sometimes people whose indirect tests are negative are positive on this test.

There are two kinds of ehrlichiosis, both of which are caused by tick-borne rickettsial parasites called Ehrlichia that infect different kinds of white blood cells. In HME (human monocytic ehrlichiosis), they infect monocytes. In HGE (human granulocytic ehrlichiosis), they infect granulocytes. HGE was renamed anaplasmosis in 2003. Ticks carry many Ehrlichia-like parasites that have not been identified yet. It is likely that the lone star tick transmits HME and that the deer tick transmits HGE.

Ehrlichiosis (HME) was originally thought to be only an animal disease. It was described in humans in 1987 and is now found in 30 states, predominately in the southeast, south-central, and mid-Atlantic states, Europe and Africa. Anaplasmosis (HGE)in humans was first identified in 1990 in a Wisconsin man. Before that it was known to infect horses, sheep, cattle, dogs and cats. It occurs in the upper midwest, northeast, the mid-Atlantic states, northern California, and many parts of Europe. Studies suggest that in endemic areas as much as 15% to 36% of the population has been infected, though often it is not recognized.

The clinical manifestations of ehrlichiosis and anaplasmosis are the same. Each is often characterized by sudden high fever, fatigue, muscle aches, headache. The disease can be mild or life-threatening. Severely ill patients can have low white blood cell count, low platelet count, anemia, elevated liver enzymes, kidney failure and respiratory insufficiency. Older people or people with immune suppression are more likely to require hospitalization. Deaths have occurred.

Diagnosis is limited by our current ability to test for only two species. Ehrlichia parasites multiply inside host cells, forming large mulberry-shaped clusters called morulae which doctors can sometimes see on blood smears. The infection still can easily be missed. The doctor may suspect ehrlichiosis/anaplasmosis in a patient who does not respond well to treatment for Lyme disease.

The treatment of choice for ehrlichiosis/anaplasmosis is doxycycline, with rifampin recommended in case of treatment failure.