The ehrlichiosis bacteria is transmitted via a bite from the lone star tick. It was named after the army base where the first known person was infected in Fort Chaffee, Arkansas.
Although the condition was known to occur in animals, it wasn't until the mid-1980s that the first cases were reported in humans.
What causes ehrlichiosis?
The lone star tick can cause ehrlichiosis through bites. The tick is native to the eastern U.S., as well as Mexico.
Ehrlichiosis is a condition that occurs as the result of a bite from a lone star tick, or Amblyomma americanum. This tick can transmit bacteria called E. chaffeensis, which is also known as rickettsia.
The lone star tick is prevalent in much of the eastern United States (U.S.) and Mexico. In the U.S., cases have been reported from coastal New England to western Texas.
While the condition is not considered as serious as tick-transmitted Lyme disease, some cases have been life-threatening.
People are more likely to be infected with ehrlichiosis in the spring and summer months, as they spend more time outdoors.
The bacteria Ehrlichia ewingii can also cause ehrlichiosis in humans. This bacteria is very similar to E. chaffeensis and will cause similar symptoms.
Symptoms of ehrlichiosis begin about 1-2 weeks after an infected tick has bitten a person. While there are some common symptoms associated with the disease, they can vary from person to person.
Symptoms of ehrlichiosis include:
- eye redness
- malaise, or feeling generally unwell
- muscle pain
According to the Centers for Disease Control and Prevention (CDC), an estimated 60 percent of children will experience a rash as a result of ehrlichiosis, compared to 30 percent of adults.
If a rash does occur, it usually does not itch. The rash does not typically appear on the face but may appear on the palms and the soles of the feet. Sometimes, the rash can look like a sunburn and cause swelling, peeling, and redness.
Not all people who are bitten by a lone star tick will have the symptoms associated with ehrlichiosis. Some people will have no symptoms or symptoms too mild to recognize.
What conditions are associated with ehrlichiosis?
Ehrlichiosis may initially cause similar symptoms to other diseases related to tick bites. Examples of these include:
- Lyme disease
- Rocky Mountain spotted fever
Unlike Rocky Mountain spotted fever and Lyme disease, ehrlichiosis is most likely to affect older adults or people with a weakened immune system.
Additionally, a rash is much less common in ehrlichiosis than in other tick-related diseases. However, the lone star tick can also carry bacteria known to cause Rocky Mountain spotted fever.
Some possible symptoms of ehrlichiosis are headaches, fever, chills, and nausea.
Ehrlichiosis can be difficult to diagnose, as the affected person may not know they have a tick bite and the condition's symptoms are similar to other illnesses, such as the flu.
A blood test is available to check for antibodies, which the immune system develops in response to a tick bite. However, these do not usually appear until a week after the bite.
A doctor will usually begin by asking about a person's symptoms, and when they started noticing the symptoms. It is important to determine if a person has recently been bitten by a tick or has visited an area where ticks are common.
A doctor will also likely order laboratory tests. These tests check for:
- increased liver enzymes
- decreased platelet count
- decreased white blood cell count
During the first week of illness, a doctor may test a person's blood for tick-borne pathogens using a polymerase chain reaction or PCR assay.
Doctors can also examine blood under a microscope for the presence of morulae, which are collections of Ehrlichia bacteria in white blood cells.
A doctor would ideally diagnose a person quickly, but if symptoms continue for longer than 7-10 days, a doctor may order a test for antibodies to the Ehrlichia bacteria.
Other tests for ehrlichiosis include an indirect immunofluorescence assay (IFA). This test is rarely used and requires multiple blood samples at different times to test for the body's immune response to the organisms.
Doctors will commonly prescribe the antibiotic doxycycline to treat ehrlichiosis.
The earlier a person takes this antibiotic, the less likely it is that the condition will have long-lasting effects. A doctor may prescribe antibiotics without having blood test results, to ensure a person who has been bitten by a tick gets prompt treatment.
If symptoms do not improve within 1-3 days after beginning treatment, the person probably does not have ehrlichiosis. However, it is important that the person takes the full course of antibiotics for them to be effective.
In rare instances, such as due to allergies or pregnancy, a person may not be able to take doxycycline. In these situations, a doctor may prescribe a different antibiotic, called rifampin.
If a person has been bitten by a tick but is not experiencing symptoms, doctors do not usually recommend taking doxycycline as a preventive measure. Doing so may delay the onset of the condition, which can make the treatment slower.
Doctors also prescribe doxycycline to treat other diseases that occur due to tick bites, including Rocky Mountain spotted fever and anaplasmosis.
If a person does not receive treatment and their symptoms progress, they can experience complications that include:
- prolonged fever
- adult respiratory distress syndrome
- blood clotting disorders
- seizures and coma
If these complications occur, a doctor will treat them in addition to the underlying infection.
Can ehrlichiosis be prevented?
Wearing clothing that fully covers the limbs can help a person avoid a tick bite. Wearing light-colored clothing can make it easier to spot ticks.
Prevention of ehrlichiosis involves taking steps to avoid getting a tick bite.
If people live in an area with lone star ticks, they can help prevent ehrlichiosis by:
- wearing long-sleeved shirts, long pants, and hats when camping or hiking
- wearing light-colored clothing to make ticks easier to spot
- checking clothing and skin for ticks after being outdoors
- tucking pants into socks to make it harder for ticks to reach the skin
- checking pets for ticks after returning from the outdoors
Exposure to fields and wooded areas puts a person at greatest risk for getting a tick bite.
According to the CDC, ehrlichiosis is fatal in 1.8 percent of cases.
However, serious complications and fatality are more common in individuals with a weakened immune system. Cancer treatments, HIV, prior organ transplants, and some medications can compromise the immune system.
The majority of people make a full recovery from ehrlichiosis, especially if they received antibiotics in good time and took them as instructed.