Tick-borne Pathogens Detected in the Blood of Immunosuppressed Norwegian Patients Living in a Tick-endemic Area.

Background: The knowledge regarding the occurrence and the clinical implications of tick-borne infections in immunosuppressed patients living in tick-endemic areas is limited.

Methods: Adult patients with autoimmune conditions requiring immunosuppressive treatment such as infliximab and rituximab were invited to participate in the study when they attended the hospital for treatment and/or control of the disease. Whole-blood samples were analyzed by real-time polymerase chain reaction for Borrelia burgdorferi sensu lato, Borrelia miyamotoi, Anaplasma phagocytophilum, Rickettsia spp., Candidatus Neoehrlichia mikurensis, and Babesia spp.

Results: The occurrence of tick-borne pathogens in the blood of patients (n = 163) with autoimmune conditions requiring immunosuppressive treatment was evaluated. Pathogen DNA was detected in 8.6% (14/163) of the patients. The predominant pathogen was Ca. Neoehrlichia mikurensis (12/14), which was carried in the blood of infected patients for 10-59 days until treatment with doxycycline. B. burgdorferi s.l. and Rickettsia spp. were detected in 1 patient each. The B. burgdorferi-infected patient presented with fever, whereas the remaining patients were judged to have subclinical infections. B. miyamotoi, A. phagocytophilum, and Babesia spp. were not detected in any patient.

Conclusions: Patients treated with biologicals and living in a tick-endemic area seem to have a high risk of contracting Ca. Neoehrlichia mikurensis infection, which, if left untreated, could result in thromboembolic complications.