Lyme Disease and Related Tick-Borne Infections - Ehrlichiosis

Human Granulocytic Anaplasmosis (HGA)

In addition to Lyme disease, I. scapularis deer ticks can carry other types of infections that cause disease in humans. Human granulocytic anaplasmosis (HGA) is another illness spread by the deer tick. (HGA was formerly called human granulocytic ehrlichiosis. Another type of ehrlichiosis, human monocytic ehrlichiosis, is carried by a different type of tick.)

Typical HGA symptoms appear very suddenly within 4 - 14 days of being bitten by an infected tick. Symptoms include headache, fever, chills, headache, and muscle pains. Vomiting, diarrhea, and loss of appetite are also common. Blood tests may indicate a low blood platelet count, low white blood cell count, and increased liver enzyme levels.

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HGA is caused by a species of bacteria called Anaplasma phagocytophilum. A blood test can identify the presence of this bacterium.

All patients who show signs of symptoms should be treated with doxycycline to reduce the risk of complications. Another type of antibiotic, rifampin, is an alternative option for pregnant women, children younger than 8 years of age, or patients who are allergic to doxycycline. Treatment is not recommended for people who do not exhibit symptoms, even if they test positive for antibodies to A. phagocytophilum.

Review Date: 01/18/2007
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital