Molecular and Serological Detection of Anaplasma phagocytophilum in Dogs from Germany (2008–2020)

SIMPLE SUMMARY: The bacterium Anaplasma phagocytophilum can cause granulocytic anaplasmosis in domestic animals, wildlife, and humans. The pathogen is transmitted by ticks and is predominantly endemic in Central and Northern Europe. We discuss the percentages of dogs that tested positive for A. phagocytophilum by direct detection of the pathogen (4.9%) and by detecting antibodies (23.3%). We found a statistically significant impact of seasonality and years of testing on PCR results as well as sex, age, years of testing and seasonality on antibody results. The dynamics of infections with A. phagocytophilum in dogs in Germany are consistent with peaks in vector activity. There is a notable increase in canine granulocytic anaplasmosis in Germany over the time of this study, which calls for increased attention and demonstrates its rising importance in clinical practice. ABSTRACT: Anaplasma phagocytophilum is an obligate intracellular bacterium that causes granulocytic anaplasmosis in domestic animals, wildlife, and humans and is primarily transmitted by ticks of the Ixodes persulcatus complex. This retrospective study aims to determine the percentages of dogs that tested positive for A. phagocytophilum in Germany. It included the results of direct (polymerase chain reaction [PCR]) and indirect (immunofluorescence antibody test [IFAT], antibody-enzyme-linked immunosorbent assay [ELISA]) detection methods performed in the laboratory LABOKLIN on canine samples provided by German veterinarians from 2008 to 2020. Out of a total of 27,368 dogs tested by PCR, 1332 (4.9%) tested positive, while 24,720 (27.4%) of the 90,376 dogs tested by IFAT/ELISA had positive serology. High rates of positive PCR results were observed in months with known peaks in vector activity, showing that the dynamics of A. phagocytophilum infections in dogs in Germany are consistent with vector activity. In dogs with a positive PCR result, peaks in serology could be observed four weeks after initial testing. Male and senior dogs had higher rates of positive serology. A possible impact of environmental factors such as changes in climate should be investigated further. Overall, the upward trend in positive test results over the years indicates that canine granulocytic anaplasmosis will continue to become increasingly important for veterinary medicine.