Borrelia B-cell Diagnostics

The investigators propose a single center, prospective observational study in children with Lyme disease (LD), the Borrelia B-cell diagnostics (BRILLIANT) study, to assess the immune response against Borrelia burgdorferi (Bb) with the following main objectives: 1. Development of Bb-specific ASC ELISpot as a new test method for diagnosis of early LD. There is an urgent unmet clinical need for a better diagnostic tool for early LD, as the current standard two-tier testing has low sensitivity in recently infected patients and may show false positive results in recovered patients due to long-term persistence of antibodies against Bb. The measurement of Bb-specific ASC with the ELISpot assay my has the potential to overcome these issues and to improve diagnosis in early LD. 2. Extensive analysis of the immune response in LD. The immune response in LD is not well understood. Large-scale studies assessing the detailed immune cell subsets/phenotypes present in blood, CSF, or synovial fluid of LD patients with respective manifestations are lacking. 3. Isolation and characterization of causative Bb species. Existing literature suggests that Bb genospecies and/or genotypes may determine virulence and manifestations, but large-scale studies assessing Bb genospecies/genotypes in different manifestation of LD are lacking. 4. Collection of clinical data about symptoms, severity, routine laboratory and diagnostic test results, treatment, and outcome of LD. 5. Biobanking samples for analysis in the future. Project population Inclusion criteria: Children, 0-17 years of age, at University Children's Hospital Zurich: * LD differential diagnosis cohort: Patients presenting at the ED with differential diagnosis of LD according to the treating physician. * Control cohort: Previously healthy patients (HC) with routine blood investigations presenting at the ED or PID outpatient department Exclusion criteria: Primary or secondary immunodeficiency.