Causes, incidence, and risk factors: Ehrlichiosis is a disease caused by Ehrlichia organisms. It was first described in 1990. The two specific organisms that have been implicated are Ehrlichia chaffeensis and the Ehrlichia phagocytophilia group. Ehrlichia chaffeensis causes a syndrome called human monocytic ehrlichiosis (HME), and the Ehrlichia phagocytophilia group causes a syndrome called human granulocytic ehrlichiosis (HGE).
The Ehrlichia bacteria belong to the family Rickettsiae. Rickettsial organisms are responsible for a number of serious diseases worldwide such as Rocky Mountain spotted fever, and� typhus. All of these diseases require an insect (tick, flea, mite) to transmit them to humans or other animals.
The infectious organism of ehrlichiosis is transmitted to humans by the bite of a tick. Rickettsiae are often associated with a specific tick. Ehrlichia inhabit the Lone Star tick, the American dog tick, and the deer tick (the deer tick is also the carrier of Lyme disease).
In the U.S., ehrlichiosis (the HME variety) is found mainly in the southern central states and the Southeast. HGE is transmitted by the deer tick like Lyme disease, so it has the same distribution in the United States as Lyme disease, mainly the Northeast and upper Midwest.
Risk factors for ehrlichiosis include living in an area with a lot of ticks, activities in high grasses, and owning a pet that may bring a tick home.
Symptoms: The incubation period for ehrlichiosis is approximately 9 days from the time of tick bite. Ehrlichiosis begins with fever, chills, headache, muscle pain, and nausea. A rash appears in less than half of the cases and the disease may be mistaken for Rocky Mountain spotted fever. The symptoms are often quite general, but the infected person is sometimes sick enough to seek medical attention.
Surveys show that the majority of people exposed did not seek treatment, and likely never knew they were infected. Ehrlichiosis is rarely fatal. The organism is sensitive to antibiotics and treatment results in improvement in 24 to 48 hours. Recovery takes 3 weeks.
Symptoms:
Signs and tests: - CBC shows decreased white blood cells (leukopenia)
- A� granulocyte stain shows clumps of the ehrlichia organism inside white blood cells
- The platelet count shows decreased platelets (thrombocytopenia)
- Liver enzymes show elevated transaminase
- A�fluorescent antibody test may turn positive for E. chaffeensis or granulocytic Ehrlichia
Treatment: Rickettsial diseases, in general, are often responsive to a group of antibiotics belonging to the tetracyclines. Treatment with tetracycline or doxycycline produces rapid improvement. Note: Oral tetracycline is usually not prescribed for children until after all the permanent teeth have erupted; it can permanently discolor teeth that are still forming.
Expectations (prognosis): With treatment full recovery is expected.
Complications: Infection may damage many organ systems, but typically the lungs and kidney are involved. Several cases have resulted in death.
Calling your health care provider: Call your health care provider if you have had a recent tick bite, or exposure to tick-infested areas, and have developed symptoms suggestive of ehrlichiosis. Be sure to mention the tick exposure to the health care provider.
Prevention: Ehrlichiosis is spread by tick bites. Preventing tick bites will prevent Ehrlichiosis and other tick-borne diseases. Common measures include the use of insect repellent, appropriate clothing, sticking to trails and avoiding dense brush when hiking, and not standing under overhanging foliage. After hiking or outings in the woods it is a good idea to examine yourself for ticks and remove any that may be found.
Studies suggest that a tick must be attached for at least 24 hours in order to cause disease, so early removal will prevent infection. The date and time of a tick bite should be recorded, as the incubation period of some tick-borne diseases is long enough that the event could be forgotten (for example, the incubation period for Lyme disease is up to 1 month).
