Severe tick-borne encephalitis in a patient previously infected by West Nile virus

We describe severe tick-borne encephalitis (TBE) in a patient who had previously experienced West Nile fever, another flavivirus infection endemic in Hungary. Previous West Nile virus infection does not develop immunity either against TBE virus infection or the disease, and it does not mitigate its clinical course. The possibility of antibody-dependent enhancement is considered.