Improving specific detection and updating phylogenetic data related to Anaplasma platys-like strains infecting camels (Camelus dromedarius) and their ticks

In camels and their infesting ectoparasites, specific detection of pathogenic Anaplasma platys and genetically related strains (A. platys-like strains) remains problematic. This requires sequencing of the hemi-nested PCR products specific to A. platys and related strains. In this study, a PCR/RFLP method, earlier developed for specific detection of A. platys-like strains in animal species other than camels, was adapted in order to subtype A. platys-like strains isolated from camels and their ticks and to differentiate them from pathogenic A. platys without going through a sequencing step. This approach was used for investigating the infections with A. platys and related strains in 412 Camelus dromedarius camels and 334 feeding ticks from five Tunisian governorates. Microscopic examination using Giemsa-stained blood smears was performed in order to specify which types of cells were infected. Ticks were identified as Hyalomma dromedarii (n = 164, 49%), H. impeltatum (n = 161, 48.3%) and H. excavatum (n = 9, 2.7%). A. platys was not detected in any of the tested camels or ticks. The overall prevalence of A. platys-like strains was 5.6% (23/412) in camels and microscopic examination of infected cells showed a tropism for neutrophil granulocytes. One tick identified as H. dromedarii out of 327 analyzed ticks was found to be infected with A. platys-like strains (0.3%). Alignment, identity comparison and phylogenetic analysis of the 16S rRNA partial sequences obtained in this study suggest that Tunisian dromedaries and feeding ticks are infected with different Anaplasma strains genetically related to A. platys. Sequence analysis and phylogenetic study based on the groEL gene confirm the RFLP results and show that camel strains formed a separate sub-cluster relatively close to A. platys-like strains infecting Tunisian cattle. This adapted RFLP assay allows fast and specific detection of pathogenic A. platys and A. platys-like strains in camels and infesting ticks and has the intrinsic potential of revealing co-infections with these two types of bacteria in the same sample, reducing the time and costs associated with cloning and sequencing during molecular diagnosis.