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human granulocytic anaplasmosis

What is human granulocytic anaplasmosis (HGA)?

Human granulocytic anaplasmosis (HGA) is an infection caused by the bacteria Anaplasma phagocytophilum. HGA bacteria infect the white blood cells of their hosts, specifically a group of cells called granulocytes.

How is HGA transmitted?

In California, people get HGA when they are bitten by a western black-legged tick infected with HGA bacteria. Ticks become infected with HGA bacteria when they bite an infected wild rodent. If that tick later bites a human, the tick may transmit the HGA bacteria to the person. Dogs and horses can be infected with HGA bacteria, but they cannot transmit the infection to people.

What are the symptoms of HGA?

Most individuals infected with HGA bacteria have no or mild symptoms. When symptoms occur, they resemble the flu, with fever, headache, fatigue, muscle aches, and nausea. Some individuals may also have vomiting, cough, or a rash. Some patients, particularly elderly persons or those with weakened immune systems, may have a more severe illness and need to be hospitalized. HGA is rarely fatal.

How is HGA diagnosed and treated?

Blood tests are available to help your doctor determine whether your illness is HGA. HGA can be successfully treated with antibiotics. Persons with HGA generally begin to feel better within one to two days of starting antibiotic treatment.

How common is HGA?

Most cases of HGA occur in the upper midwestern and northeastern United States. HGA is an uncommon infection in California; only six confirmed cases occurred between 1994 and 2006.

How can I prevent HGA?

Taking appropriate precautions to avoid tick bites can reduce the risk of HGA, as well as
other diseases transmitted by ticks.

What can be done to keep from being bitten by ticks?

  • Avoid areas where ticks are known to occur.
  • Stay in the middle of trails; avoid grassy areas, contact with logs, tree trunks and fallen branches or tree limbs in forests. 
  • Use an EPA registered repellent for use against ticks. Repellents with at least 20% DEET are effective and can be applied to the skin and clothing. Always follow directions on the container. 
  • Apply permethrin to clothing (only) to kill ticks.
  • Thoroughly check yourself and others for ticks during and up to three days after activities in tick-infested areas.
  • Shower soon after returning from tick habitat.
  • Before washing, place clothing worn while in tick habitat in a hot dryer for 10 minutes to kill ticks crawling on clothing.
  • Keep grass along trails, buildings, and camping areas mown.

How should attached ticks be removed?

Note: Prompt tick removal can prevent disease transmission.
  • Using tweezers, grasp the tick's mouthparts as close to the skin as possible.
  • Gently pull the tick straight out, using a firm steady motion.
  • Wash your hands and the bite site with soap and water.
  • Apply an antiseptic to the bite site.
  • See your Healthcare Provider if you develop any symptoms, especially a rash, within 30 days of the tick bite.

Where can I find more information on HGA?

The U.S. Centers for Disease Control and Prevention has information available on their anaplasmosis webpage.    ​
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If you are having difficulty accessing any items on this webpage please contact CDPH at 916-552-9730 or email VBDS@cdph.ca.gov to request this information in an alternate format.​

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