A friend of mine was bitten by a tick during a camping trip and went to the doctor with a rash. She thought she had Lyme disease, but she was diagnosed with something called ehrlichiosis. I've never heard of this before. Is it anything like Lyme? How do you tell the difference? Are the risks, prevention and treatment the same? Someone else on the same camping trip also got Lyme disease from a tick bite. Do the same ticks carry both diseases?

Cal

Ehrlichiosis is a relatively uncommon infection caused by a few different bacteria. Like Lyme disease, ehrlichiosis is transmitted by ticks. There are two main forms of this infection -- human monocytic ehrlichiosis (HME) and human granulocytic ehrlichiosis (HGE) -- named after the human cells (monocytes or granulocytes) that are involved. HME has been reported to occur in about 30 different states, but it is seen most often in the south central and southeastern states, areas where another tickborne infection, Rocky Mountain spotted fever, commonly occurs. While Lyme disease can occur in these areas, it is much more common in the northeast and the northwest United States, which also are the areas where HGE is seen. This less common infection is transmitted by the same tick (Ixodes scapularis) that transmits Lyme disease. Patients with both Lyme disease and HGE often are unaware of having been bitten by a tick because the species that transmits both diseases is quite small.

Aside from the fact both are transmitted by the same type of tick, Lyme disease and ehrlichiosis have little else in common. Shortly after infection, patients with Lyme disease usually develop a red, ring-shaped "bull's-eye" rash, which slowly enlarges, often leaving a clear center. A few more such lesions can develop throughout the body over the ensuing days to weeks. This rash should not be confused with the rash seen in about 10 to 35 percent of patients with ehrlichiosis, which consists of macules and papules (spots and bumps) -- much smaller than the Lyme disease bull's-eye lesions -- scattered throughout the body. Most patients with ehrlichiosis also develop a high fever, as well as respiratory and gastrointestinal complaints -- symptoms that are uncommon in Lyme disease.

Sometimes diagnosis is complicated by the fact that two diseases can occur together. When this happens, a patient can develop the typical skin lesions of Lyme disease, but may also be infected with HGE. It is important not to miss the diagnosis of HGE because without treatment, this infection can have serious complications, including seizures, coma and even death. HME also can be difficult to diagnose, as it is sometimes confused with Rocky Mountain spotted fever.

The treatment of both forms of ehrlichiosis usually involves a tetracycline such as doxycycline (Vibramycin and others). This is also the drug of choice for Rocky Mountain spotted fever and is one of the options for early Lyme disease. Amoxicillin (Amoxil and others) can be used for Lyme disease, but it is not effective treatment for ehrlichiosis. If there is any doubt about whether the patient is infected with both Lyme disease and ehrlichiosis, doxycycline would be the better choice.