Verification of a case of mixed infection with Lyme disease, tick-borne encephalitis and COVID-19

Background. The relationship between pathogens of new diseases and tick-borne infections is an underinvestigated direction in the problem of infectious diseases.The aim. To show the features of identifying the markers of Borrelia burgdorferi, tickborne encephalitis and SARS-CoV-2 pathogens on the example of a case of a triple mixed infection (Lyme disease, tick-borne encephalitis and COVID-19) and using comprehensive studies.Methods. In 2019–2021, a comprehensive study of 7 blood samples from a patient with mixed infection was carried out. We used real-time polymerase chain reaction (PCR), enzyme immunoassay (ELISA) and determined antigen, IgM, IgG antibodies, and avidity index (AI) of IgG antibodies.Results. Ixodid tick-borne borreliosis was diagnosed in a patient 5 months after contagion. Only high-avid Lyme-IgG antibodies were detected. Low-avid Lyme- IgG antibodies appeared against the background of a reduced general condition. At the same time, high-avid IgG (cut-off index (COI) – 7.8) and IgM (COI = 1.2) antibodies to the TBE virus were detected. In July 2020, the patient was infected with SARSCoV-2. TBE virus which passed into the body simultaneously with Borrelia in the fall of 2019 was activated. Although the patient did not have specific symptoms of TBE, in subsequent blood samples (No. 4, 5, 6) we found TBEV antigen (optical density (OD) – 4.3; 1.9 and 2.0 respectively) and IgM (COI = 1.3; 0,9 and 0 respectively). These results were recognized as TBEV activation, which contributed to an increase in the avidity of IgG antibodies (AI = 65 %; 100 % and 63 % respectively). IgM antibodies to SARSCoV-2 virus were not detected, as opposed to the high levels of IgG (COI = 8.2; 8.1; 8.4 and 14.7 respectively).Conclusions. Therefore, using not only the common methods of diagnosing (PCR and ELISA), but also the determination of the antibody avidity degree, we have shown that when analyzing a case of a triple mixed infection, B. burgdorferi dominates in the human body and causes a long-term chronic course of the disease.