Bogovič et al.
Comparison of clinical, laboratory and immune characteristics of the monophasic and biphasic course of tick-borne encephalitis.
Microorganisms. 2021; 9(4):796. doi: 10.3390/microorganisms9040796

TBE caused by the European subtype of TBE virus usually has a biphasic course and the clinical manifestations are generally well described. Much less is known about the monophasic course.

A Slovenian team has analyzed and compared in detail clinical and laboratory characteristics in 705 patients aged at least 18 years (283 monophasic and 422 biphasic course of disease) from 2007-2012. In this study, the acute form of illness was meningoencephalitis (62.1%).

Patients with the monophasic course had higher severity score and more often needed treatment in intensive care unit. Patients with the monophasic course were older and had a higher proportion of underlying diseases, and they had a longer duration of illness prior to diagnosis and more pronounced disruption of the blood-brain barrier as indicated by higher albumin and IgG index. No distinctions however were found two to seven years after TBE with regards to the frequency of post encephalitis syndrome (analyzed for 412 patients): 32% vs. 34%, as well as its severity. No substantial differences were seen when various cytokines/chemokines were compared. However, patients with the monophasic course had higher CSF levels of immune mediators representing innate Th1 and B-cell immune responses.

Patients with the monophasic course were more often vaccinated against TBE (7.4% vs. 0.9%). The authors found a strong association of the monophasic course of TBE with previous vaccination. Among patients with TBE despite vaccination, 84% had the monophasic course of illness versus 38.5% of unvaccinated patients.

In summary, the monophasic course is associated with more difficult disease course, but the long-term outcome is similar.

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