Ehrlichiosis is a tick-borne disease caused by the bacteria Ehrlichiae. The first human case in the U.S. was reported in 1986, in a man exposed to ticks in Arkansas. In New York State, most cases of ehrlichiosis have been diagnosed in Westchester County and the lower Hudson Valley.

Anyone can get ehrlichiosis, although the majority of known cases have been in adults. People who spend time outdoors in tick infested areas from April until October are at greatest risk for exposure.

As with Lyme disease, ehrlichiosis is believed to be spread by ticks, including the deer tick, the dog tick and the lone star tick. Transmission occurs after a bite from an infected tick. Ehrlichiosis cannot be spread from person to person.

The most common symptoms are fever, muscle aches, weakness and headache. Patients may also experience confusion, nausea, vomiting and joint pain. Unlike Lyme disease or Rocky Mountain spotted fever, a rash is not common. Infection usually produces mild to moderately severe illness, with high fever and headache, but may occasionally be life-threatening or even fatal.

The incubation period is usually one to three weeks after exposure to an infected tick. However, not every exposure results in infection.

Special laboratory tests can detect recent infection with the Ehrlichia bacteria. Other laboratory findings may include low white blood count, low platelet count and abnormal liver enzyme tests. Because diagnostic tests are not readily available, the diagnosis of ehrlichiosis should be made based on clinical symptoms and a history of exposure to ticks.

Tetracycline antibiotics are usually rapidly effective for ehrlichiosis. Because these antibiotics can cause dental staining in children, physicians should consult an infectious disease expert when treating children.

As with Lyme disease, avoiding tick bites will prevent ehrlichiosis. When working or playing outdoors in tick infested areas: Wear light colored clothing and tuck pants into socks, tuck shirt into pants: Apply repellents containing DEET to exposed skin and clothing: Use repellents sparingly and avoid prolonged or excessive applications, especially in children: Check clothes and body surfaces carefully after being outdoors, especially in tick infested areas.