Development of a tick-borne encephalitis serodiagnostic ELISA using recombinant Fc-antigen fusion proteins

A Sensitive Nano Luciferase Immune Complex Assay System for Highly Sensitive and Specific Detection of Antibodies Against Tick-Borne Encephalitis Virus

Tick-borne encephalitis virus (TBEV) can cause fever, headache, neurological disorders, and/or peripheral flaccid paralysis; therefore, it is a major threat to public health. A rapid, sensitive, and simple method for detecting anti-TBEV antibodies is needed urgently to determine infection and for vaccine evaluation. Here, a luciferase-based immunocomplex assay system (Luc-IC) was developed to detect TBEV antibodies. The system is based on a reporter Nano luciferase (NLuc) that is co-expressed as a fusion protein with viral envelope domain III (ED3) in COS7 cells. The cell supernatant was used directly to detect antigen without the need for a purification step. This simple procedure effectively improved the sensitivity of the assay. Sera from 50 patients with an acute tick-borne encephalitis infection were tested to determine the sensitivity of the NLuc-IC assay. Furthermore, 62 sera from individuals infected with Japanese encephalitis virus, West Nile virus, yellow fever virus, dengue virus, or Zika virus were also tested to determine specificity. The results demonstrated that the assay was 100% sensitive and 100% specific for TBEV antibodies. Thus, this very simple NLuc-IC assay is potentially useful for rapid and accurate diagnosis of TBEV infection in both humans and animals.

Comparison of six commercial tick-borne encephalitis IgM and IgG ELISA kits and the molecular characterization of their antigenic design

Tick-borne encephalitis virus (TBEV) diagnosis is mainly based on the detection of viral-specific antibodies in serum. Several commercial assays are available, but published data on their performance remain unclear. We assessed six IgM and six IgG commercial enzyme-linked immunosorbent assay (ELISA) kits (ELISA-1 through ELISA-6) using 94 samples, including precharacterized TBEV-positive samples (n=50) and -negative samples (n=44). The six manufacturers showed satisfactory sensitivity and specificity and high overall agreement for both IgM and IgG. Three manufacturers showed better reproducibility and were the most sensitive (100%) and specific (95.5-98.1%) for both IgM and IgG. Two of them were also in agreement with the clinical interpretation in more than 90% of the cases. All the assays use inactivated virus as antigen, with strains showing approximately 94% homology at the amino acid level. The antigenic format of the assays was discussed to further improve this TBEV diagnostic tool.