Human monocytic ehrlichiosis
Encyclopedia
Human monocytotropic ehrlichiosis (HME) is a form of ehrlichiosis
associated with Ehrlichia chaffeensis
.
This bacteria is an obligate intracellular pathogen affecting monocytes and macrophages.
) thrive.
HME occurs in California in Ixodes pacificus ticks and in Dermacentor variabilis ticks.
Nearly 600 cases were reported to the CDC in 2006. In 2001-2002, the incidence was highest in Missouri, Tennessee, and Oklahoma, as well as in people older than 60.
, headache
, malaise, and muscle aches (myalgia
). Compared to Human Granulocytic Ehrlichiosis, rash is more common. Laboratory abnormalities include thrombocytopenia
, leukopenia
, and elevated liver tests.
The severity of the illness can range from minor or asymptomatic to life-threatening. CNS involvement may occur. A serious septic or toxic shock-like picture can also develop, especially in patients with impaired immunity.
Ehrlichia serologies can be negative in the acute period. PCR is therefore the laboratory diagnostic tool of choice.
is the treatment of choice.
Presentation during early pregnancy can complicate treatment.
Rifampin has been used in pregnancy and in patients allergic to doxycycline.
Ehrlichiosis
Ehrlichiosis is a tick-borne disease of dogs usually caused by the organism Ehrlichia canis. Ehrlichia canis is the pathogen of animals. Humans can become infected by E. canis and other species after tick exposure. German Shepherd dogs are thought to be particularly affected by the disease, other...
associated with Ehrlichia chaffeensis
Ehrlichia chaffeensis
Ehrlichia chaffeensis is a species of rickettsiales bacteria.It is named for Fort Chaffee.It is the causative agent of human monocytic ehrlichiosis....
.
This bacteria is an obligate intracellular pathogen affecting monocytes and macrophages.
Ecology & Epidemiology
HME occurs across the south-central, southeastern, and mid-Atlantic states, regions where both the white-tailed deer (Odocoileus virginianus) and lone star ticks (Amblyomma americanumAmblyomma americanum
Amblyomma americanum, or lone star tick, is a species of tick in the genus Amblyomma. It's average length is 1/4 inch.-Distribution:...
) thrive.
HME occurs in California in Ixodes pacificus ticks and in Dermacentor variabilis ticks.
Nearly 600 cases were reported to the CDC in 2006. In 2001-2002, the incidence was highest in Missouri, Tennessee, and Oklahoma, as well as in people older than 60.
Symptoms
The most common symptoms are feverFever
Fever is a common medical sign characterized by an elevation of temperature above the normal range of due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.As a person's temperature increases, there is, in...
, headache
Headache
A headache or cephalalgia is pain anywhere in the region of the head or neck. It can be a symptom of a number of different conditions of the head and neck. The brain tissue itself is not sensitive to pain because it lacks pain receptors. Rather, the pain is caused by disturbance of the...
, malaise, and muscle aches (myalgia
Myalgia
Myalgia means "muscle pain" and is a symptom of many diseases and disorders. The most common causes are the overuse or over-stretching of a muscle or group of muscles. Myalgia without a traumatic history is often due to viral infections...
). Compared to Human Granulocytic Ehrlichiosis, rash is more common. Laboratory abnormalities include thrombocytopenia
Thrombocytopenia
Thrombocytopenia is a relative decrease of platelets in blood.A normal human platelet count ranges from 150,000 to 450,000 platelets per microliter of blood. These limits are determined by the 2.5th lower and upper percentile, so values outside this range do not necessarily indicate disease...
, leukopenia
Leukopenia
Leukopenia is a decrease in the number of white blood cells found in the blood, which places individuals at increased risk of infection....
, and elevated liver tests.
The severity of the illness can range from minor or asymptomatic to life-threatening. CNS involvement may occur. A serious septic or toxic shock-like picture can also develop, especially in patients with impaired immunity.
Diagnosis
Tick exposure is often overlooked. For patients living in high-prevalence areas who spend time outdoors, a high degree of clinical suspicion should be employed.Ehrlichia serologies can be negative in the acute period. PCR is therefore the laboratory diagnostic tool of choice.
Treatment
If Ehrlichiosis is suspected, treatment should not be delayed while waiting for a definitive laboratory confirmation, as prompt doxycycline therapy has been associated with improved outcomes. DoxycyclineDoxycycline
Doxycycline INN is a member of the tetracycline antibiotics group, and is commonly used to treat a variety of infections. Doxycycline is a semisynthetic tetracycline invented and clinically developed in the early 1960s by Pfizer Inc. and marketed under the brand name Vibramycin. Vibramycin...
is the treatment of choice.
Presentation during early pregnancy can complicate treatment.
Rifampin has been used in pregnancy and in patients allergic to doxycycline.
See also
- monocyteMonocyteMonocytes are a type of white blood cell and are part of the innate immune system of vertebrates including all mammals , birds, reptiles, and fish. Monocytes play multiple roles in immune function...
- Human granulocytic ehrlichiosis
- Human granulocytic anaplasmosisHuman granulocytic anaplasmosisHuman granulocytic anaplasmosis is an infectious disease caused by Anaplasma phagocytophilum, an obligate intracellular bacterium that is typically transmitted to humans by at least three kinds of ticks, including Ixodes scapularis, Ixodes pacificus, and Dermacentor variabilis...
- Human ewingii ehrlichiosisHuman ewingii ehrlichiosisEhrlichiosis ewingii infection is an infectious disease caused by an intracellular bacteria, Ehrlichia ewingii. The infection is transmitted to humans by Amblyomma americanum...