Los Angeles County West Vector & Vector-Borne Disease Control District

Erlichiosis

What is ehrlichiosis?
    Ehrlichiosis is the general name used to describe several bacterial diseases that affect animals and humans. These diseases are caused by the organisms in the genus Ehrlichia. Worldwide, there are currently four ehrlichial species that are known to cause disease in humans.
   
Human ehrlichiosis due to Ehrlichia chaffeensis was first described in 1987. The disease occurs primarily in the southeastern and south central regions of the country and is primarily transmitted by the lone star tick, Amblyomma americanum (see photo to right)
   
Human granulocytic ehrlichiosis (HGE) represents the second recognized ehrlichial infection of humans in the United States, and was first described in 1994. The name for the species that causes HGE has not been formally proposed, but this species is closely related or identical to the veterinary pathogens Ehrlichia equi and Ehrlichia phagocytophila.  HGE is transmitted by the blacklegged tick (Ixodes scapularis) and the western blacklegged tick (Ixodes pacificus) in the United States.
   
Ehrlichia ewingii is the most recently recognized human pathogen. Disease caused by E. ewingii has been limited to a few patients in Missouri, Oklahoma, and Tennessee, most of whom have had underlying immunosuppression. The full extent of the geographic range of this species, its vectors, and its role in human disease is currently under investigation.

How do people get ehrlichiosis?
   
In the United States, ehrlichiae are transmitted by the bite of an infected tick. The lone star tick (Amblyomma americanum), the blacklegged tick (Ixodes scapularis), and the western blacklegged tick (Ixodes pacificus) are known vectors of ehrlichiosis in the United States. Ixodes ricinus is the primary vector in Europe.

What are the symptoms of ehrlichiosis?
   
The symptoms of ehrlichiosis may resemble symptoms of various other infectious and non-infectious diseases. These clinical features generally include fever, headache, fatigue, and muscle aches. Other signs and symptoms may include nausea, vomiting, diarrhea, cough, joint pains, confusion, and occasionally rash. Symptoms typically appear after an incubation period of 5-10 days following the tick bite. It is possible that many individuals who become infected with ehrlichiae do not become ill or  they develop only very mild symptoms.

In the United States, where do most cases of ehrlichiosis occur?
   
Most cases of ehrlichiosis are reported within the geographic distribution of the vector ticks (click on map below). Occasionally, cases are reported from areas outside the distribution of the tick vector. In most instances, these cases have involved persons who traveled to areas where the diseases are endemic, and who had been bitten by an infected tick and developed symptoms after returning home. Therefore, if you traveled to an ehrlichiosis-endemic area 2 weeks prior to becoming ill, you should tell your doctor where you traveled.

  Areas where human ehrlichiosis may occur based on approximate distribution of vector tick species
(Click on Map)
Map - Areas where human ehrlichiosis may occur


How is ehrlichiosis diagnosed?
    A diagnosis of ehrlichiosis is based on a combination of clinical signs and symptoms and confirmatory laboratory tests. Your doctor can send your blood sample to a reference laboratory for testing. However, the availability of the different types of laboratory tests varies considerably. Other laboratory findings indicative of ehrlichiosis include low white blood cell count, low platelet count, and elevated liver enzymes.

How is ehrlichiosis treated?
    Ehrlichiosis is treated with a tetracycline antibiotic, usually doxycycline.

Can a person get ehrlichiosis more than once?
   
Very little is known about immunity to ehrlichial infections. Although it has been proposed that infection with ehrlichiae confers long-term protection against reinfection, there have been occassional reports of laboratory-confirmed reinfection. Short-term protection has been described in animals infected with some Ehrlichia species and this protection wanes after about 1 year. Clearly, more studies are needed to determine the extent and duration of protection against reinfection in humans.


 (Information and images on this page from the (Centers for Disease Control and Prevention)

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