Anaplasma phagocytophilum


Human granulocytic anaplasmosis is a febrile disease that can be caused by the bacterium Anaplasma phagocytophilum. The bacteria are transmitted to humans by ticks.


In Europe, everywhere where there are ticks. However, the differences between countries and within countries are large.

Pathogen reservoir

Known hosts are horses, dogs, ruminants, hedgehogs and wild boars. The most common vector in Europe is the common wood tick(Ixodes ricinus), a species of tick.

Infection route

Transmission to humans occurs through tick bites. Transmission by blood transfusion or from mother to child during birth can occur, but is rare.

Incubation period

The incubation period varies between 5 to 21 days


Up to 75 percent of all anaplasma infections proceed without any recognizable signs of illness. After an incubation period of about five to 30 days, flu-like symptoms (high fever, headache, aching limbs, muscles and joints) may occur. Rarely, abdominal pain, nausea, vomiting and diarrhea occur. Severe complications such as multiple organ failure, meningitis, and acute respiratory distress syndrome may occur in people with compromised immune systems.


For anaplasmosis, the antibiotic doxycycline is the drug of choice for adults and children of all ages.


A vaccine is not currently available, so care should be taken to protect against tick bites.

Situation in Austria

In veterinary medicine, the pathogen has been known since 1932, and the first infection in humans was reported in the 1990s. For the first time, Anaplasma phagocytophilum DNA was detected in the common wood tick(Ixodes ricinus) and deer in 2002. The presence of Anaplasma in ticks and deer has been repeatedly confirmed since then. Human diseases with source of infection in Austria are very rare but severe courses have been documented.

Specialized information

The vector of A. phagocytophilum in Europe is the tick species Ixodes ricinus. The prevalence of A. phagocytophilum in different countries ranges from 0.5% to 34% , with high variability within and between countries. In Central and Eastern Europe, high variability in prevalence was found in different countries, ranging from low levels in Hungary and Moldova (0.5%-2.4%) to intermediate levels in Slovakia and Russia (8%-9%) to high levels of 34% in Bulgaria.

Therapy: use of doxycycline should be initiated when clinically suspected. Therapy is most effective when started early in the course of illness. Doxycycline is highly effective, and there are no reports of posttherapeutic relapse. Treatment usually responds rapidly and results in significant clinical improvement within 24 to 72 hours. A possible alternative for patients with doxycycline allergy or mild disease during pregnancy is rifampicin.


Although human anaplasmosis has been reported very rarely in Austria, it should be considered as a differential diagnosis in patients with fever with low leukocyte and platelet counts and elevated C-reactive protein after a tick bite.

The standard serologic test for the diagnosis of anaplasmosis is the indirect immunofluorescence assay (IFA). Examination of paired serum samples allows detection of a significant (fourfold) increase in antibody titers. This improves the validity of the serology. The first sample should be collected during the first week of illness; the result is often negative. The second sample is taken 2 to 4 weeks later. IgM antibodies are less specific than IgG antibodies and can lead to false positive results. IgM results alone should not be used for laboratory diagnosis. During the acute phase of illness, whole blood analysis by polymerase chain reaction (PCR) can be performed. This method is highly sensitive at the onset of illness; however, sensitivity may decrease after antibiotic use has begun.

Last updated: 09.03.2023

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