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Human granulocytic anaplasmosis

Published on March 8, 2024 at 8:00 / Updated on March 26, 2024 at 8:00

Human granulocytic anaplasmosis (HGA) is a tick-borne infection caused by a bacteria.

In most cases, HGA is not serious and will get better on its own. Some people will have no symptoms while others may experience the following flu-like symptoms:

  • Fever
  • Fatigue
  • Discomfort
  • Joint and muscle pain
  • Headaches
  • Coughing
  • Nausea and vomiting

Symptoms develop within 5 to 21 days after being bitten by a tick carrying the bacteria. Symptoms can begin quickly and be very intense.

This infection can also cause blood problems and damage certain organs. For example, a person could experience a decrease in the number of platelets or white blood cells.

Causes and triggers

The infection is caused by a bacteria transmitted to humans by ban infected tick. The tick must feed on the blood of animals or humans to grow. Most tick bites are painless and often go unnoticed. Adult ticks span around 1 to 3 millimetres before feeding but can triple in size when filled with blood, becoming as big as an apple seed.

Immature ticks, which are called nymphs, can also transmit the infection. Nymphs are tiny and remain attached to the skin for longer before being detected. Infected ticks typically need to remain attached to the skin for 24 to 48 hours or more to transmit the bacteria.

Ticks do not fly or jump. They are normally found in forests, woodlands, tall grass, and piles of dead leaves. They are mainly present and active in the spring, summer, and fall.

Ticks carrying HGA are present all over Canada, the United States, and other countries. Certain parts of the country are at greater risk of having ticks carrying this bacteria. It's important to keep in mind that not all ticks are infected. Ticks can also carry other germs and transmit other infections, such as Lyme disease.

Adult ticks at various stages of engorgement.

(Approximate size)

More severe cases of HGA can occur, especially in seniors or people with weak immune systems.


The best way to prevent human granulocytic anaplasmosis is to avoid being bitten by an infected tick. Here are a few recommendations to follow:

  • Stay on trails during nature walks.
  • Wear long pants tucked into your socks, a shirt with long sleeves that fit snugly at the wrists, closed-toe shoes, and a hat when walking in tall grass or wooded areas.
  • Wear long, light-coloured clothing that will make it easier to see ticks.
  • Wear clothes that are treated with permethrin, an insecticide.
  • Apply an insect repellent such as DEET or icaridin on all exposed body parts, except the face.
  • Inspect yourself and others, pets, and equipment for ticks when returning from high-risk areas.

If, despite taking these measures, you find a tick that has managed to latch onto your skin, remove it as soon as possible. Here's how to proceed:

  • Using a small pair of tweezers or another tool designed for this purpose, grasp the tick as close to the skin's surface as possible (not by its body), and gently pull upwards without twisting.
  • Do not grab the tick with your fingers.
  • Clean the bite area with soap and water.

Antibiotic treatment may be necessary if you develop symptoms of the infection.

When should I see a health care professional?

If you get bitten by a tick, talk to your health care provider to see if you need treatment.

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