Ehrlichiosis

What is ehrlichiosis?

Ehrlichiosis is an acute disease of humans and animals caused by bacteria named Ehrlichia. These organisms, which are transmitted by ticks, can infect two different types of white blood cells.

Where does ehrlichiosis occur?

One type of ehrlichiosis, caused by the bacterium Ehrlichia chaffeensis, occurs primarily in the south central and southeastern United States. This particular organism, which infects the white blood cells called monocytes, has been known to exist for several years and has caused hundreds of cases of human illness. A new type of Ehrlichia is now known to occur in Wisconsin, Minnesota, and certain northeastern states. This recently discovered Ehrlichia has not yet been named, but because it infects the white blood cells known as granulocytes, the illness it causes is referred to as human granulocytic ehrlichiosis.

Who gets ehrlichiosis?

Although all persons are susceptible to the disease, persons who spend time outdoors in tick-infested environments are at an increased risk of exposure. In the upper midwest, the risk of tick exposure is highest from late spring through autumn.

How is ehrlichiosis spread?

The bacteria are transmitted to humans by the bite of infected ticks. In the southern USA, the lone star tick (Amblyomma americanum) is thought to be responsible for transmission. In the upper midwest, the agent of human granulocytic ehrlichiosis is probably transmitted by the deer tick (Ixodes scapularis), the same tick responsible for the spread of Lyme disease.

What are the symptoms of ehrlichiosis?

The symptoms are generally nonspecific and can range from very mild to very severe illness. Most patients will experience fever, muscle pain, severe headache and shaking chills. Less frequent signs and symptoms include nausea, vomiting, acute weight loss, mental confusion, cough, and skin rash.

How soon do symptoms occur?

Symptoms typically begin between one and three weeks after exposure.

How is ehrlichiosis diagnosed?

Certain laboratory test results can suggest a diagnosis of ehrlichiosis. These include a low white blood cell count, low platelet count, and an elevation in certain liver function tests. The definitive diagnosis involves specialized blood tests which detect the Ehrlichia agent itself or the presence of antibodies against the bacterium. Tests developed for E. chaffeensis infection will generally not be able to detect an infection with the agent of human granulocytic ehrlichiosis.

What is the treatment for ehrlichiosis?

The disease tends to respond very well to tetracycline type antibiotics like doxycycline.

What precautions can be taken to prevent getting ehrlichiosis?

Prevention hinges upon avoiding tick bites. When in areas which may be tick-infested, the following precautions can reduce the risk of getting ehrlichiosis:

Wear a long-sleeved shirt, long pants, socks, and closed shoes (rather than sandals). Tuck your shirt into your pants and your pant cuffs into tops of socks. Light-colored clothing will make any ticks on them more easily visible. Walk in the center of cleared or mowed trails to avoid brushing up against shrubs and tall grass.

Conduct thorough tick checks on yourself and your children after spending time in a tick-infested area, and promptly remove any ticks found.

Insect repellents containing 0.5% permethrin or 20-30% DEET have been shown to be effective in repelling deer ticks. If such products are used, be sure to follow the manufacturer's directions on the label.

How should an attached tick be removed?

To remove a tick that has attached to the skin, grasp the tick with a pair of narrow-bladed tweezers or forceps as close as possible to the attachment (skin) site, and pull outward with a firm steady traction. If tweezers are not available, the fingertips can be used, but should be shielded from the tick with tissue paper or rubber gloves. Avoid squeezing or puncturing the body of the tick because it may contain infectious fluids. After tick removal, wash the bite site and your hands with soap and water, and apply a disinfectant or an antibiotic ointment to the site.

Each year, Medical College of Wisconsin physicians care for more than 180,000 patients, representing nearly 500,000 patient visits. Medical College physicians practice at Children's Hospital of Wisconsin, Froedtert Memorial Lutheran Hospital, the Milwaukee VA Medical Center, and many other hospitals and clinics in Milwaukee and southeastern Wisconsin.