Multiple-locus variable-number tandem repeat analysis potentially reveals the existence of two groups of Anaplasma phagocytophilum circulating in cattle in France with different wild reservoirs

Abstract

Background: Anaplasma phagocytophilum is the causative agent of tick-borne fever, a disease with high economic impact for domestic ruminants in Europe. Epidemiological cycles of this species are complex, and involve different ecotypes circulating in various host species. To date, these epidemiological cycles are poorly understood, especially in Europe, as European reservoir hosts (i.e. vertebrate hosts enabling long-term maintenance of the bacterium in the ecosystem), of the bacterium have not yet been clearly identified. In this study, our objective was to explore the presence, the prevalence, and the genetic diversity of A. phagocytophilum in wild animals, in order to better understand their implications as reservoir hosts of this pathogen.

Methods: The spleens of 101 wild animals were collected from central France and tested for the presence of A. phagocytophilum DNA by msp2 qPCR. Positive samples were then typed by multi-locus variable-number tandem repeat (VNTR) analysis (MLVA), and compared to 179 previously typed A. phagocytophilum samples.

Results: Anaplasma phagocytophilum DNA was detected in 82/101 (81.2%) animals including 48/49 red deer (98%), 20/21 roe deer (95.2%), 13/29 wild boars (44.8%), and 1/1 red fox. MLVA enabled the discrimination of two A. phagocytophilum groups: group A contained the majority of A. phagocytophilum from red deer and two thirds of those from cattle, while group B included a human strain and variants from diverse animal species, i.e. sheep, dogs, a horse, the majority of variants from roe deer, and the remaining variants from cattle and red deer.

Conclusions: Our results suggest that red deer and roe deer are promising A. phagocytophilum reservoir host candidates. Moreover, we also showed that A. phagocytophilum potentially circulates in at least two epidemiological cycles in French cattle. The first cycle may involve red deer as reservoir hosts and cattle as accidental hosts for Group A strains, whereas the second cycle could involve roe deer as reservoir hosts and at least domestic ruminants, dogs, horses, and humans as accidental hosts for Group B strains.

Keywords: Anaplasma phagocytophilum; France; Group A; Group B; MLVA; Red deer; Reservoir; Roe deer; VNTR; Wild boars.

Fig. 1

Minimum spanning tree of the 198 A. phagocytophilum database samples according to their host species. Each circle represents a unique MLVA profile. The number of circle partitions corresponds to the number of A. phagocytophilum samples with the same genotype. Circles connected by a shaded background and tick lines differ by a maximum of one of the five VNTR markers, and could be considered as a “clonal complex”. The length of each branch is proportional to the number of differences. Each animal host species is represented by a specific color in the circle

Fig. 2

Minimum spanning tree of the 198 A. phagocytophilum samples according to the abortion status of their hosts. Each circle represents a unique MLVA profile. The number of circle partitions corresponds to the number of A. phagocytophilum samples with the same genotype. Circles connected by a shaded background and tick lines differ by a maximum of one of the five VNTR markers, and could be considered as a “clonal complex”. The length of each branch is proportional to the number of differences. Anaplasma phagocytophilum obtained from cattle that have aborted are red, and those from cattle that have not are green. Anaplasma phagocytophilum obtained from other host species are represented in white