Human granulocytic anaplasmosis
|Human granulocytic anaplasmosis|
|Classification and external resources|
|eMedicine||med/3391 ped/655 emerg/159|
Human granulocytic anaplasmosis (HGA) (previously known as Human granulocytic ehrlichiosis, or HGE ) 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. These ticks also transmit Lyme disease and other diseases.
Ecology and epidemiology
A. phagocytophilum is transmitted to humans by Ixodes ticks. These ticks are found in the US, Europe, and Asia. In the US, I. scapularis is the tick vector in the East and Midwest states, and I. pacificus in the Pacific Northwest.
The major mammalian reservoir for A. phagocytophilum in the eastern United States is the white-footed mouse, Peromyscus leucopus. Although white-tailed deer harbor A. phagocytophilum, evidence suggests that they are not a reservoir for the strains that cause HGA.
Anaplasma phagocytophilum shares its tick vector with other human pathogens, and about 10% of patients with HGA show serologic evidence of coinfection with Lyme disease, babesiosis, or tick-borne meningoencephalitis.
Signs and symptoms
Signs and symptoms may include fever, severe headache, muscle aches (myalgia), chills and shaking, similar to the symptoms of influenza. Additional signs and symptoms may also include nausea, vomiting, loss of appetite, unintentional weight loss, abdominal pain, cough, diarrhea, aching joints, sensitivity to light, weakness, fatigue, change in mental status (extreme confusion, memory loss, inability to comprehend environment- interaction, reading, etc.), and temporary loss of basic motor skills (no permanent cases have been reported). Symptoms may be minor, as evidenced by surveillance studies in high-risk areas. Gastrointestinal tract symptoms occur in less than half of patients and a skin rash is seen in less than 10% of patients. It is also characterized by a low number of platelets, a low number of white blood cells, and elevated serum transaminase levels in the majority of infected patients. Even though people of any age can get human anaplasmosis, it is usually more severe in the aging or immune-compromised. Some severe complications may include respiratory failure, kidney failure, and secondary infections.
Clinically, HGA is essentially indistinguishable from Human monocytic ehrlichiosis, the infection caused by Ehrlichia chaffeensis, and other tick-borne illnesses such as Lyme disease may be suspected. As Ehrlichia serologies can be negative in the acute period, PCR is very useful for diagnosis.
Treatment and Prevention
Doxycycline is the treatment of choice. If anaplasmosis is suspected, treatment should not be delayed while waiting for a definitive laboratory confirmation, as prompt doxycycline therapy has been shown to improve outcomes. Presentation during early pregnancy can complicate treatment. Doxycycline compromises dental enamel during development. Although rifampin is indicated for post-delivery pediatric and some doxycycline-allergic patients, it is teratogenic. Rifampin is contraindicated during conception and pregnancy. Currently, there is no vaccine against human granulocytic anaplasmosis.
Although the infectious agent is known to be from the Anaplasma genus, the term "human granulocytic ehrlichiosis" (HGE) is often used, reflecting the prior classification of the organism. E. phagocytophilum and E. equi were reclassified as Anaplasma phagocytophilum.
- Human monocytic ehrlichiosis
- Human ewingii ehrlichiosis
- Ehrlichiosis (canine)
- Ticks of domestic animals
- CDC Emerging Infectious Diseases for more information about HGE
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