Abstract
BackgroundEquine Granulocytic Anaplasmosis (EGA) is caused by Anaplasma phagocytophilum, a tick-transmitted, obligate intracellular bacterium. In Europe, it is transmitted by Ixodes ricinus. A large number of genetic variants of A. phagocytophilum circulate in nature and have been found in ticks and different animals. Attempts have been made to assign certain genetic variants to certain host species or pathologies, but have not been successful so far. The purpose of this study was to investigate the causing agent A. phagocytophilum of 14 cases of EGA in naturally infected horses with molecular methods on the basis of 4 partial genes (16S rRNA, groEL, msp2, and msp4).ResultsAll DNA extracts of EDTA-blood samples of the horses gave bands of the correct nucleotide size in all four genotyping PCRs. Sequence analysis revealed 4 different variants in the partial 16S rRNA, groEL gene and msp2 genes, and 3 in the msp4 gene. One 16S rRNA gene variant involved in 11 of the 14 cases was identical to the "prototype" variant causing disease in humans in the amplified part [GenBank: U02521]. Phylogenetic analysis revealed as expected for the groEL gene that sequences from horses clustered separately from roe deer. Sequences of the partial msp2 gene from this study formed a separate cluster from ruminant variants in Europe and from all US variants.ConclusionsThe results show that more than one variant of A. phagocytophilum seems to be involved in EGA in Germany. The comparative genetic analysis of the variants involved points towards different natural cycles in the epidemiology of A. phagocytophilum, possibly involving different reservoir hosts or host adaptation, rather than a strict species separation.
Highlights
Equine Granulocytic Anaplasmosis (EGA) is caused by Anaplasma phagocytophilum, a tick-transmitted, obligate intracellular bacterium
Before 2001, when a reclassification based on 16S rRNA gene similarities was proposed, the causing agent of EGA was known as Ehrlichia equi, which was part of the E. phagocytophila group
Genetic variations have been found previously on basis of the 16S rRNA, groEL, msp2, msp4 and ankA gene in A. phagocytophilum from ticks and animals, it was not possible to attribute genetic variants to a certain host or geographic origin [3,5,6,7,28,29,30]. These investigations showed that A. phagocytophilum seems to show certain genetic heterogeneity; because of this we hypothesised that genetic heterogeneity would exist in A. phagocytophilum naturally infecting horses and causing EGA
Summary
Equine Granulocytic Anaplasmosis (EGA) is caused by Anaplasma phagocytophilum, a tick-transmitted, obligate intracellular bacterium. The purpose of this study was to investigate the causing agent A. phagocytophilum of 14 cases of EGA in naturally infected horses with molecular methods on the basis of 4 partial genes (16S rRNA, groEL, msp, and msp). Genetic variations have been found previously on basis of the 16S rRNA, groEL, msp, msp and ankA gene in A. phagocytophilum from ticks and animals, it was not possible to attribute genetic variants to a certain host or geographic origin [3,5,6,7,28,29,30] These investigations showed that A. phagocytophilum seems to show certain genetic heterogeneity; because of this we hypothesised that genetic heterogeneity would exist in A. phagocytophilum naturally infecting horses and causing EGA. More than one partial 16S rRNA gene variant was involved in equine infection and genetic variations were detected in the other amplified parts of genes
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