Factors associated with Anaplasma phagocytophilum infection in sheep in Iran

Abstract

Anaplasma phagocytophilum is one of the most widespread tick-borne pathogens in sheep across the world. The aim of this cross-sectional study was the determination of the molecular prevalence and associated risk factors of A. phagocytophilum infection in sheep populations of Iran. For this aim, between March 2018 and February 2019 jugular vein blood samples were collected from 1782 apparently healthy sheep from nine provinces from four ecological zones of Iran. Specific nested-PCR targeting the 16S rRNA gene of A. phagocytophilum was employed. Twelve 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. DNA of Anaplasma phagocytophilum was detected in 8.1 % of animals (144/1782). Among geographical zones, the prevalence was highest in the Persian Gulf zone (P<0.001); and among provinces Mazandaran (in the north) had the highest prevalence (P < 0.001). The multivariate analysis revealed that no/irregular application of ectoparasiticides (OR=2.09, P < 0.001), short-distance between farms (less than 1km) (OR=1.96, P = 0.011), and high-density barns (<1.5 m2 /head) (OR = 1.45, P = 0.050) are potential risk factors of A. phagocytophilum infection in sheep from Iran. The spatial scan statistic in SaTScan recognized three high risks clusters for A. phagocytophilum infection in Caspian (Mazandaran Province) and the Persian Gulf (Khuzestan Province) zones amongst the study areas (P < 0.001). Phylogenetic analysis based on A. phagocytophilum 16S rRNA genes revealed significant nucleotide sequence identities between the sequences obtained in this study with those previously collected from other countries. This research is the largest study focusing on ovine anaplasmosis in Iran and shows that infected sheep are present in all zones, and geographic areas. The connection between A. phagocytophilum and its transmission routes in the country e.g. ticks, iatrogenesis, and economic impact of the infection remains largely unknown and warrants further investigation.