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Abstract To carry out effective genome-wide association studies, information about linkage disequilibrium (LD) is essential. Here, we used medium-density SNP chips to provide estimates of LD in native Tunisian cattle. The two measures of LD that were used, mean r2 and D’, decreased from 0.26 to 0.05 and from 0.73 to 0.40, respectively, when the distance between markers increased from less than 20 Kb to 200 Kb. The decay in LD over physical distance occurred at a faster rate than that reported for European and other indigenous breeds, and reached background levels at less than 500 Kb distance. This is consistent with the absence of strong selective pressure within the Tunisian population and suggests that, in order to be effective, any potential genome-wide association mapping studies will need to use chips with higher marker density. An analysis of effective population size (Ne) based on LD data showed a decline in past Ne, with a sudden drop starting about eight generations ago. This finding, combined with the high levels of recent inbreeding revealed by runs of homozygosity (ROH) analysis, indicate that this population is endangered and may be in urgent need of a conservation plan that includes a well-designed genetic management program.

In cattle, anaplasmosis is a tick-borne rickettsial disease caused by Anaplasma marginale , A. centrale , A. phagocytophilum , and A. bovis. To date, no information concerning the seasonal dynamics of single and/or mixed infections by different Anaplasma species in bovines are available in Tunisia. In this work, a total of 1035 blood bovine samples were collected in spring (n = 367), summer (n = 248), autumn (n = 244) and winter (n = 176) from five different governorates belonging to three bioclimatic zones from the North of Tunisia. Molecular survey of A. marginale , A. centrale and A. bovis in cattle showed that average prevalence rates were 4.7% (minimum 4.1% in autumn and maximum 5.6% in summer), 7% (minimum 3.9% in winter and maximum 10.7% in autumn) and 4.9% (minimum 2.7% in spring and maximum 7.3% in summer), respectively. A. phagocytophilum was not detected in all investigated cattle. Seasonal variations of Anaplasma spp. infection and co-infection rates in overall and/or according to each bioclimatic area were recorded. Molecular characterization of A. marginale msp4 gene indicated a high sequence homology of revealed strains with A. marginale sequences from African countries. Alignment of 16S rRNA A. centrale sequences showed that Tunisian strains were identical to the vaccine strain from several sub-Saharan African and European countries. The comparison of the 16S rRNA sequences of A. bovis variants showed a perfect homology between Tunisian variants isolated from cattle, goats and sheep. These present data are essential to estimate the risk of bovine anaplasmosis in order to develop integrated control policies against multi-species pathogen communities, infecting humans and different animal species, in the country. [ABSTRACT FROM AUTHOR]

Few data are available about the presence and distribution of Anaplasma species in cattle in North African countries. In this study prevalence, co-infections, risk factors and genetic diversity of Anaplasma species were evaluated in bovines from Northern Tunisia. A total of 232 cattle from 36 randomly selected farms in three Tunisian localities were investigated for the presence of Anaplasma species in blood by Real-time PCR and/or nested PCR. Overall infection rates of Anaplasma spp., Anaplasma marginale , Anaplasma centrale and Anaplasma bovis were 34.9%, 25.4%, 15.1%, and 3.9%, respectively. Anaplasma phagocytophilum was not detected in cattle. The most common co-infection pattern was an association of A. marginale and A. centrale (11.2%). Five cattle (2.1%) all reared in the sub-humid bioclimatic area, were co-infected by the three Anaplasma species. Molecular prevalence of Anaplasma infection varied significantly according to locality, bioclimatic area, tick infestation and type of breeding. Animals of the Holstein breed were less infected by A. marginale and A. centrale than other breeds. Genetic analysis of A. marginale msp4 gene indicated a high sequence diversity of Tunisian strains, suggesting a multiple introduction of infected cattle from different origins. Phylogenetic studies based on the 16S rRNA gene showed that the most prevalent A. centrale strains were closely related to the A. centrale vaccine strain. Moreover, all A. bovis variants clustered with other A. bovis sequences obtained from domestic and wild ruminant strains. This is the first molecular investigation on Anaplasma species in Tunisian cattle providing pivotal background for designing epidemiological studies and to develop control strategies in the country. [ABSTRACT FROM AUTHOR]