Schizophrenia prevalence in the United States is highest in urbanized Northeastern, Northwestern, and Great Lakes States. The viral theory of schizophrenia attributes this distribution to enhanced susceptibility to viral infections in crowded, urban areas. Such infections during fetal or perinatal development are hypothesized to result in the eventual onset of schizophrenia. This study attempts to identify which viral infections have a similar geographical distribution to schizophrenia. Examination of the geographical distribution of infectious diseases in the United States reveals that the spreading foci of
Lyme disease and its primary vectors, Ixodid ticks, correlate significantly with high schizophrenia rate areas. Ixodid ticks are vectors in North America and throughout the world of tick-borne encephalitis (TBE). The international distribution of TBE is shown to be concentrated in countries where the highest rates of schizophrenia are found: Croatia, Norway, Finland, Germany, Ireland, and others. The geographical specificity of this correlation and the plausibility of a tick-associated or TBE theory of schizophrenia are discussed.