Human granulocytic anaplasmosis (HGA) - Fact Sheet


What is human granulocytic anaplasmosis?
Human granulocytic anaplasmosis (HGA) is an infection caused by a bacterium. The bacteria invade and live within white blood cells called granulocytes. HGA is a newly recognized disease that is emerging in areas with high rates of Lyme disease.

How is HGA spread?
HGA is transmitted to humans through the bite of a tick. In Connecticut, the Ixodes scapularis (black-legged or deer) tick transmits HGA. This is the same tick that transmits Lyme disease.

Who gets HGA?
Although everyone is susceptible to the disease, people who spend time outdoors in tick infested areas are at an increased risk of exposure.

What are the symptoms of HGA?
Not everyone infected with HGA becomes sick. The symptoms of HGA infections are mostly nonspecific, and the illness can range from very mild to very severe. Most patients will experience a rapid onset of fever, shaking chills, muscle or joint pain, and severe headache. Less frequent symptoms may include malaise, nausea, vomiting, acute weight loss, and skin rash.

How soon do symptoms appear?
Symptoms of HGA usually start within 7-21 days of the tick bite.

How long can an infected person carry HGA?
If a person is treated with antibiotics, HGA infection goes away quickly. However, if treatment is not given, HGA can stay in a person’s blood for up to 4 weeks or possibly longer.

How is HGA diagnosed?
HGA can be diagnosed by blood tests, either by measuring your body’s immune response to the infection, or by testing for DNA of the bacteria. Usually to get confirmed results, blood needs to be drawn twice, once when you first get sick and again 4-6 weeks later.

What is the treatment for HGA?
HGA can be effectively treated with antibiotics, usually doxycycline, so it is important to visit your health care provider if you think that you may have an HGA infection. Since it is possible to become infected with HGA and Lyme disease at the same time, be sure to seek medical attention if you become ill after a tick bite.

How can HGA be prevented?
To prevent HGA and other tick-borne infections, the best protection is to avoid contact with ticks. When working or playing outside in areas that ticks inhabit (tall grass and weeds, scrubby areas, woods and leaf litter) you should:

  • Wear light colored clothing (to spot the ticks easily), long sleeved shirts and long pants.
  • Create a “tick barrier” by tucking pants into socks and shirt into pants.
  • Consider using insect repellent, according to manufacturer’s instructions, when planning to be outdoors.
  • Check clothing and skin very carefully (especially thighs, groin, arms, underarms, legs and scalp) after being outdoors in tick infested areas and remove any ticks promptly.
  • Wash the area with soap and water and apply an antiseptic when the tick has been removed.
  • Keep your lawn mowed, cut overgrown brush, and clear any leaf litter away from the home.
  • Inspect pets daily and remove any ticks found.

How should a tick be removed?

  • It is important that a tick is removed as soon as it is discovered.
  • Remove the tick as soon as possible using tweezers. Grasp the tick mouth parts as close to the skin as possible and pull the tick out with steady pressure. Do not yank the tick out. Do not crush the ticks body as it may contain infectious fluids.
  • Do not use petroleum jelly, hot matches, nail polish remover, or any other substance to remove a tick. By using these substances, you may actually increase your chance of infection.
  • Thoroughly wash the area of the bite with soap and water and put an antiseptic on it.
  • Check after every 2 to 3 hours of outdoor activity for ticks attached to clothing or skin.
  • The sooner the tick is removed, the lesser the risk of tick-borne infection.
  • Write on the calendar the date you removed the tick and the part of the body it was removed from.
  • Contact your physician for recommendations on testing and treatment.



This fact sheet is for informational purposes only. It should not be used for self-diagnosis or as a substitute for consultation with a health care provider. If you think that you may have this infection, or have questions about the disease described above, you should consult your health care provider.



For additional information on this disease, visit the Centers for Disease Control and Prevention website.







To contact the Epidemiology and Emerging Infections Program, please call 860-509-7994.