Prevalence of Anaplasma phagocytophilum in Ixodes ricinus and Dermacentor reticulatus and Coinfection with Borrelia burgdorferi and Tick-Borne Encephalitis Virus in Western Ukraine

Introduction: Tick-borne encephalitis virus (TBEV) and Borrelia burgdorferi, the causative agent of Lyme disease (LD), are widespread in Western Ukraine. However, relatively little is known about Anaplasma phagocytophilum in this region. This study examined patterns of infection with A. phagocytophilum in two tick vectors compared with the better studied TBEV and B. burgdorferi. Materials: Ticks were collected in three different ecosystems of the Western Ukraine during 2009-2014. Samples were examined for pathogen detection using real-time polymerase chain reaction (PCR), and logistic regression models were developed to assess the significance of different factors. Results: Among the three selected ecological systems of the Western region of Ukraine, 5130 ticks belonging to Ixodes ricinus and Dermacentor reticulatus were collected between 2009 and 2014. They were grouped into 366 pools and were tested by PCR for A. phagocytophilum. A subsample (1620 ticks, 162 pools) of the ticks was concurrently tested by PCR for A. phagocytophilum, B. burgdorferi, and TBEV. Overall, there was no trend in the proportion of positive ticks across years (p > 0.05). However, the prevalence of A. phagocytophilum was higher (27.4%) in I. ricinus than in D. reticulatus (15.9%) (OR = 2.69; 95% CI, 1.52-4.94 (Lower, Upper 95% CI)). Infection was more common in forested habitats (OR = 1.89; 95% CI, 1.07-3.36) and during the later summer-early autumn (3.78; 95% CI, 1.79-8.06). B. burgdorferi was found in 29.3% and 31.9% of I. ricinus and D. reticulatus, respectively; and TBEV was found in 6.3% and 14.5% of I. ricinus and D. reticulatus. Coinfection of A. phagocytophilum and B. burgdorferi occurred more often than chance and was more frequent than any other combination of pathogens (p = 0.031). Conclusions: Our study is the first to explore the potential relationship between the ecosystems, vectors, and the presence of Human Granulocytic Anaplasmosis (HGA) and other tick-borne infections in Western Ukraine. Anaplasma demonstrated a greater prevalence in I. ricinus in the forested area in Western Ukraine. Altogether, HGA, LD, and tick-borne encephalitis (TBE) pathogens are actively circulating in these ecosystems and have the potential to coinfect vectors that might increase the risk of transmitting multiple pathogens to humans during host feeding by individual ticks.