Figure 1.

Overview of the classic biphasic disease-pattern of human TBEV infection. The viremic first phase includes influenza-like symptoms and occurs around 1 week after virus transmission. It is estimated that 65–70% of infected individuals clear the virus after this phase, but for one third of the patients, an asymptomatic disease phase follows before the second phase of disease begins. In this phase, symptoms of meningitis or encephalitis occur, including fever, headache, tremor, nystagmus, altered state of consciousness, cranial nerve paralysis, and spinal nerve paralysis. Classically, no virus is detected in sera or plasma in the second phase of disease. Around 30% of patients that enter the second phase of disease will suffer from long lasting sequeale, with a decreased quality of life. Figure compiled from Lindquist and Vapalahti (3), Taba et al. (4), and Haglund and Gunther (6).