Background: BDV causes immunopathology of the central nervous system in many animal species. Detection is based on serology and PCR. Due to low viremia, it is hard to detect and antibodies are found only in 0.5% of the human population.Â Evidence suggests an association of viral infection with disorders like bipolar disease and schizophrenia. Methods and Findings: We developed a Real Time RT-PCR for BDV p40 and p24.Â A total of 212 horses were tested, 18 resulted positive for BDV RNA.Â A group of 76 human samples were also tested: 51 bipolar patients and 25 healthy volunteers. Five bipolar patients were positive for p24, three were positive for p40 and one was positive for p40 strain No98. All healthy donors were negative. Conclusions: BDV detection is reported for the first time in Costa Rica.Â Although the number of samples tested was low, a high incidence was observed in horses and a strong association in humans with bipolar disease is suggested.