Microbe of the Week is written by undergraduate researcher, Maria Bergquist

Microbe of the Week: Ehrlichia species

Welcome to microbe of the week, where we break down the different disease-causing microbes that lurk inside our tick vectors! This week’s microbe is a group of bacterial species under the genus Ehrlichia which cause Ehrlichiosis throughout the US.

What are the Ehrlichia species?

Ehrlichia bacterial species infect white blood cells, which is why bacteria in the Anaplasma genus were originally thought to be part of the Ehrlichia genus. The species of Ehrlichia that lead to Ehrlichiosis in humans in the United states are Ehrlichia chaffeensis, E. ewingii, and E. muris eauclairensis. E. canis leads to Ehrlichiosis in dogs. The reservoir hosts for E. chaffeensis and E. ewingii is primarily believed to be white-tailed deer, while dogs are considered the reservoir host of E. canis. More research is needed to identify the reservoir host of E. muris eauclairensis. Ehrlichia species are transmitted to humans by either the lone star tick (Amblyomma americanum) or the deer tick (Ixodes scapularis).

A. Adult Female Amblyomma americanum (Lone star tick) B. Adult Female Ixodes scapularis (deer tick). Photo credit: James Gathany — CDC Public Health Image Library

 More statistics on Ehrlichia species is available at:  

https://www.cdc.gov/ehrlichiosis/stats/index.html

Symptoms

Like many tick-related illnesses, the early symptoms of Ehrlichiosis (first five days of illness) are similar to other common illnesses and include fever, chills, severe headache, muscle aches, nausea, vomiting, diarrhea, loss of appetite, confusion, and in up to 1 in 3 cases a rash can form. This rash is described as either red splotches or pinpoint dots. If treatment is delayed or if the person is immunocompromised there is a risk for more severe symptoms which include damage to the brain or nervous system, respiratory failure, uncontrolled bleeding, organ failure, and death.

More information on symptoms of Ehrlichiosis is available at the CDC website: 

https://www.cdc.gov/ehrlichiosis/symptoms/index.html

Treatment

Like Lyme disease, the treatment of Ehrlichiosis is Doxycycline.

A Condensed History

• 1925 — First recognition of Ehrlichia species found in ruminants in Africa. Originally named Rickettsia ruminantium (now known as Ehrlichia ruminantium) by E.V. Cowdry.
• 1935 — Ehrlichia canis (originally named Rickettsia canis) identified in Algerian dogs by Donatien and Lestoquard.
• 1963 — E. canis found in dogs in the United States by Sidney Ewing.
• 1986 — First presumed human case of Ehrlichiosis described in the US. Patient was a 51-year-old man who was bitten by a tick in Arkansas and was believed to be infected with Ehrlichia canis.
• 1990 — First Ehrlichia chaffeensis case identified from a patient in Arkansas.
• 1999 — Four people infected with Ehrlichia ewingii in Missouri.
• 2009 — New Ehrlichia species identified. Originally named E. muris-like agent but is now known as Ehrlichia muris eauclairensis and is predominantly found in Minnesota and Wisconsin.
• 2018 — Missouri, Arkansas, New York, and Virginia accounted for more than half of all reported cases of ehrlichiosis.