Short Report: Identification of a Potential Marker of Anaplasma Phagocytophilum Associated with Cattle Abortion.

Anaplasma phagocytophilum is a tick-borne pathogen that causes tick-borne fever in domestic ruminants. Tick-borne fever is characterized by diverse symptoms and occasionally causes abortions in domestic ruminants, resulting in significant economic impact. However, in France, the potential frequency of A. phagocytophilum-related abortions is unknown, and thus, it remains difficult to estimate the full extent of its economic impact. This gap in our knowledge is likely explained, at least in part, by the absence of suitable and specific tools capable of detecting A. phagocytophilum associated with abortion. Our objective was to identify a genetic marker able to differentiate A. phagocytophilum strains isolated from domestic ruminants that had aborted compared to those that had not. Thus, we typed a total of 123 A. phagocytophilum obtained from cattle, of which 25 originated from cows that had aborted, via multiple-locus variable-number tandem repeat (VNTR) analysis. These included 56 new A. phagocytophilum samples and 67 previously published A. phagocytophilum samples. A multivariate logistic model demonstrated that the triple-repeat allele of the APV-A VNTR was statistically more frequent in A. phagocytophilum from cattle that had aborted, compared to A. phagocytophilum from cattle that had not aborted (P = 0.03), while controlling for any regional effects (P < 0.0001). For four other VNTR, there were no statistical associations between specific alleles and abortion. The APV-A triple-repeat VNTR allele could thus act as a marker of A. phagocytophilum involved in abortions. If this hypothesis is confirmed in additional samples from other regions, this marker could then be utilized in the development of A. phagocytophilum abortive strain surveillance measures.