Human infections with Borna disease virus: seroprevalence in patients with chronic diseases and healthy individuals.

Borna disease virus (BDV) is as yet an unclassified infectious agent which causes a neurologic disease in horses and sheep and is transmissible to other animal species. Human sera were tested for BDV-specific antibodies by immunofluorescence and immunoprecipitation. The sera were collected from three thousand subjects in Europe, the USA, and Africa classified by clinical syndromes/infectious diseases, and from healthy controls. In all three continents, positive serum samples were detected which recognized the major BDV antigen of 38/40 KD present in the nuclei of infected cells. In contrast to 2% of seropositives among the normal population, significantly higher prevalences (13-14%) were present among patients with chronic progressive diseases of the brain and the immune system. In children, antibody frequencies were two to four times higher than in adults. The results suggest a latent infection with BDV in humans leading to low antigen expression in healthy subjects and frequent reactivation events in chronically ill patients.