Ehrlichiosis

How ehrlichiosis spreads

Ehrlichia bacteria live inside white blood cells. In the US, most human cases are caused by Ehrlichia chaffeensis, carried by the lone star tick (Amblyomma americanum), recognized by a white spot on the female's back. Deer are a main animal reservoir. A related species, E. ewingii, causes similar illness, and E. muris eauclairensis has been found in the upper Midwest, spread by the blacklegged tick.

Most cases occur in the southeastern, south-central and eastern US, especially Missouri, Arkansas, Oklahoma, Tennessee, Virginia and North Carolina, from April to September. The infection is not spread person to person, though rare cases have occurred through blood transfusion or organ transplant.

Dogs can also get ehrlichiosis, usually from the brown dog tick. Dogs do not pass it directly to people, but they can bring infected ticks into the home.

Symptoms

Symptoms usually begin 1 to 2 weeks after the bite. Many people do not remember being bitten.

• fever and chills
• headache
• muscle aches
• tiredness and feeling unwell
• nausea, vomiting, diarrhea and loss of appetite
• confusion
• rash: in about 1 in 3 adults and up to 60% of children; it may be flat red spots or small pinpoint spots, often on the trunk, and appears around 5 days after fever starts

Severe illness

Without treatment, ehrlichiosis can cause:

• breathing failure from lung inflammation
• kidney failure
• bleeding problems
• meningitis or encephalitis (brain involvement)
• septic shock-like illness
• hemophagocytic lymphohistiocytosis, a dangerous immune overreaction

Severe disease is more likely in older adults, people with weakened immune systems (including HIV, chemotherapy, organ transplants and no spleen), and when doxycycline is delayed. About 1 in 100 people with ehrlichiosis die despite treatment.

Ehrlichiosis vs other tick-borne diseases

Coinfection with more than one tick-borne disease is possible.

Diagnosis

Doctors suspect ehrlichiosis from symptoms plus possible tick exposure. Typical blood test findings:

• low white blood cell count (leukopenia)
• low platelet count (thrombocytopenia)
• raised liver enzymes
• sometimes low sodium

Confirmatory tests:

• PCR on whole blood, most sensitive in the first week
• antibody tests (indirect immunofluorescence), comparing samples taken 2 to 4 weeks apart; a single early test is often negative
• occasionally, clusters of bacteria (morulae) seen inside white cells on a blood smear

Treatment should not wait for test results.

Treatment

Doxycycline is the treatment of choice for adults and children of all ages. Short courses of doxycycline for tick-borne rickettsial diseases have not been shown to cause the tooth staining seen with older tetracyclines, and the CDC and American Academy of Pediatrics recommend it for children. Treatment usually continues for at least 3 days after the fever goes away, typically 7 to 14 days in total.

Most people improve within 24 to 48 hours. Failure to improve suggests another diagnosis. Rifampin is sometimes used in pregnancy or for people with a serious doxycycline allergy, with specialist advice. Severe cases need hospital and intensive care support.

Prevention

• Use repellent: EPA-registered products containing DEET, picaridin, IR3535 or oil of lemon eucalyptus on skin; permethrin on clothing and gear.
• Cover up: long sleeves, long pants tucked into socks, light colors to spot ticks.
• Stay on trails and avoid tall grass and leaf litter.
• Check for ticks daily after being outdoors, including the scalp, armpits, groin, behind the knees and in the belly button.
• Shower within 2 hours of coming indoors.
• Remove ticks promptly with fine-tipped tweezers, pulling straight up steadily. Do not use heat, nail polish or petroleum jelly.
• Protect pets with veterinary tick prevention.

Preventive antibiotics after a tick bite are not recommended for ehrlichiosis.

Frequently asked questions

What are the symptoms of ehrlichiosis?

Ehrlichiosis causes fever, chills, headache, muscle aches and tiredness, usually 1 to 2 weeks after a tick bite. Nausea, vomiting, diarrhea, confusion and a rash can also occur. Severe cases can affect the lungs, kidneys and brain.

How is ehrlichiosis treated?

Ehrlichiosis is treated with the antibiotic doxycycline, for adults and children. It should be started as soon as ehrlichiosis is suspected, without waiting for test results. Most people improve within 1 to 2 days of starting treatment.

Which tick carries ehrlichiosis?

The lone star tick is the main carrier of ehrlichiosis in the United States. It is found in the southeastern, south-central and eastern states. The blacklegged tick spreads a related Ehrlichia species in parts of the upper Midwest.

Can ehrlichiosis be fatal?

Yes, though uncommonly. About 1% of people with ehrlichiosis die, mostly older adults, people with weak immune systems, and those whose treatment was delayed. Prompt doxycycline greatly reduces the risk.

Can you get ehrlichiosis from your dog?

Not directly. Dogs get ehrlichiosis from ticks, mostly a different species, and cannot pass it to people. However, dogs can carry ticks into your home or yard. Use tick prevention on pets and check them after outdoor time.