Anaplasmosis, formerly known as human granulocytic ehrlichiosis, is an infection caused by the bacterium Anaplasma phagocytophilum, which is transmitted to humans through tick bites. Due to non-specific symptomatology, the prevalence of the disease is probably underestimated.

What is anaplasmosis?

Human Granulocytic Anaplasmosis (HGA), formerly known as human granulocytic ehrlichiosis is an infection caused by the bacterium, Anaplasma phagocytophilum. The bacterium is transmitted to humans by a bite from a tick of the Ixodes genus, which is also the vector of Lyme borreliosis.

In 2017, 1.8% of ticks analyzed as part of the TiquesNet project (almost 1,600 ticks collected across Belgium) were infected with the bacterium. 

The main reservoir consists of rodents, bovines and deer.

Anaplasmosis is an emergent disease in human pathology, diagnosed for the first time in Belgium in 1995. Due to a non-specific symptomatology at the start of the disease, diagnostic tests are generally prescribed late, and confirmed acute infections are therefore rare. 


Asymptomatic infections are common. When the disease develops, it is characterized by a set of flu-like symptoms (fever, muscle aches, headaches, abdominal symptoms), following an incubation period of 1 to 3 weeks.

If the disease is not treated properly, severe complications can arise in the form of acute respiratory distress, hemorrhage, kidney failure or neurological problems. The disease is associated with hematological abnormalities (neutropenia, anemia and thrombocytopenia).

Sciensano is responsible for the epidemiological surveillance of anaplasmosis in humans in Belgium, as well as the population’s exposure to tick bites (through the medium of the TiquesNet project).

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