Anaplasma ovis infection in sheep from Iran: molecular prevalence, associated risk factors, and spatial clustering

The aim of this cross-sectional study was to determine the molecular prevalence and associated risk factors in sheep populations of Iran. To this end, between March 2017 and February 2018 jugular vein blood samples were collected from 1842 apparently healthy sheep from 327 herds in nine provinces in four ecological zones of Iran. A specific nested-PCR targeting the msp4 gene of A. ovis was employed. Fourteen variables were subjected to logistic regression analyses (univariate and multivariate) to specify the potential risk factors for infection. Statistically significant variables in univariate analyses (P ≤ 0.20) were assessed by multivariable logistic regression to control the confounding factors. Anaplasma ovis DNA was detected in 51.1% of herds (167/327) and 28.3% of animals (521/1842). Among geographical zones, herd and animal prevalence was highest in the Persian-Gulf zone (P < 0.001), and among provinces, Lorestan (in west) and Khuzestan (in south-west) had the highest prevalence (P < 0.001). Analysis of factors associated with A. ovis infection revealed that distance from other farms (OR = 2.52, P < 0.001), presence of other animal species in the farm (OR = 2.03, P = 0.046), season (OR = 1.40, P = 0.005), breed (OR = 3.762, P < 0.001), and age of sheep (OR = 1.20, P = 0.049) are potential risks in Iran. The spatial scan statistic in SaTScan recognized two high risks clusters for A. ovis infection in central (Semnan province) and the Persian-Gulf (Khuzestan province) zones amongst the study areas (P < 0.001). Sequence and phylogenetic analysis of the msp4 gene confirmed the detection of A. ovis. This research is the largest study focusing on ovine anaplasmosis in Iran and shows that infected sheep are present in all geographic zones, bioclimatic areas, and provinces.