Limited evidence of infection with other tick-borne pathogens in patients tested for Lyme neuroborreliosis in the Netherlands.

Ixodes ricinus is the main vector of the causative agents of Lyme neuroborreliosis. This tick species can also transmit tick-borne encephalitis virus (TBEV), spotted fever group (SFG) Rickettsia and Borrelia miyamotoi to humans. These tick-borne pathogens are present in Dutch ticks and have also been associated with human neurological infections, but well characterized disease cases are seldom reported. We therefore assessed the evidence for TBEV, SFG Rickettsia or B. miyamotoi infection in clinically well-described patients suspected of Lyme neuroborreliosis. We retrospectively included patients with specific predefined clinical criteria from patients that were tested for Lyme neuroborreliosis between 2010 and 2014 at an academic Lyme borreliosis Center. Serology was performed on available serum samples, and cerebrospinal fluid (CSF) was tested by molecular methods. Out of 514 potentially eligible patients, 176 individual patients were included. None of CSF samples was positive for the tested tick-borne pathogens, except for one previously described patient with Borrelia miyamotoi disease (BMD). Serology revealed 27, 14 and three patients with antibodies against SFG Rickettsia, B. miyamotoi and TBEV, respectively. No distinctive clinical symptoms or signs could be associated with seropositivity against any of these tick-borne pathogens. Apart from the previously published BMD case, we were unable to find convincing evidence of new cases of tick-borne encephalitis, spotted fever rickettsiosis or BMD in a cohort of patients suspected of Lyme neuroborreliosis. While antibodies against these tick-borne pathogens were detected, we could not associate these findings to clinical symptoms or signs. Therefore, prospective studies on humans with tick exposure are necessary to describe the prevalence, etiology and clinical symptoms of these tick-borne diseases other than Lyme borreliosis and tick-borne encephalitis.