''Ehrlichiosis ewingii'' infection is an

infectious disease An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable di ...

caused by an intracellular

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

, ''

Ehrlichia ewingii ''Ehrlichia ewingii'' is a species of rickettsiales bacteria. It has recently been associated with human infection, and can be detected via PCR serological testing. The name ''Ehrlichia ewingii'' was proposed in 1992. T ...

''. The infection is transmitted to humans by the tick, ''

Amblyomma americanum ''Amblyomma americanum'', also known as the lone star tick, the northeastern water tick, or the turkey tick, or the "Cricker Tick", is a type of tick indigenous to much of the eastern United States and Mexico, that bites painlessly and commonly ...

''. This tick can also transmit ''

Ehrlichia chaffeensis ''Ehrlichia chaffeensis'' is an obligate intracellular, Gram-negative species of Rickettsiales bacteria. It is a zoonotic pathogen transmitted to humans by the lone star tick (''Amblyomma americanum''). It is the causative agent of human monoc ...

'', the bacteria that causes

human monocytic ehrlichiosis Human monocytotropic ehrlichiosis is a form of ehrlichiosis associated with ''Ehrlichia chaffeensis''. This bacterium is an obligate intracellular pathogen affecting monocytes and macrophages. Symptom and signs The most common symptoms are fever, ...

(HME).

Symptoms and signs

Patients can present with fever, headache, myalgias, and malaise. Laboratory tests may reveal

thrombocytopenia Thrombocytopenia is a condition characterized by abnormally low levels of platelets, also known as thrombocytes, in the blood. It is the most common coagulation disorder among intensive care patients and is seen in a fifth of medical patients a ...

leukopenia Leukopenia () is a decrease in the number of leukocytes (WBC). Found in the blood, they are the white blood cells, and are the body's primary defense against an infection. Thus the condition of leukopenia places individuals at increased risk of in ...

, and evidence of liver damage.

Mechanism

Humans contract the disease after a bite by an infected tick of the species ''

''. Those with an underlying immunodeficiency (such as

HIV The human immunodeficiency viruses (HIV) are two species of ''Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the immune ...

) appear to be at greater risk of contracting the disease. Compared to HME, ewingii ehrlichiosis has a decreased incidence of complications. Like ''

Anaplasma phagocytophilum ''Anaplasma phagocytophilum'' (formerly ''Ehrlichia phagocytophilum'') is a Gram-negative bacterium that is unusual in its tropism to neutrophils. It causes anaplasmosis in sheep and cattle, also known as tick-borne fever and pasture fever, and ...

'', the causative agent of human granulocytic ehrlichiosis, ''Ehrlichia ewingii'' infects neutrophils. Infection with ''E. ewingii'' may delay neutrophil apoptosis.

Diagnosis

In endemic areas, a high index of suspicion is warranted, especially with a known exposure to ticks. The diagnosis can be confirmed by using PCR. A peripheral blood smear can also be examined for intracytoplasmic inclusions called morulae.

Treatment

The treatment of choice is doxycycline.

References

External links