Detection of Neospora caninum in the semen and blood of naturally infected bulls Ignacio Ferre a , Gorka Aduriz b , Itziar del-Pozo b , Javier Regidor-Cerrillo a , Raquel Atxaerandio b , Esther Collantes-Ferna ´ndez a , Ana Hurtado b , Carlos Ugarte-Garagalza c , Luis Miguel Ortega-Mora a, * a Departamento de Sanidad Animal, Facultad de Veterinaria, Universidad Complutense de Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain. b Departamento de Sanidad Animal, Instituto Vasco de Investigacio ´n y Desarrollo Agrario (NEIKER), Berreaga 1, 48160 Derio, Bizkaia, Spain. c Aberekin Centro de Inseminacio ´n, Unidades de Torrelavega y Derio, Parque Tecnolo ´gico Ed. 600, 48160 Derio, Bizkaia, Spain. Received 20 May 2004; received in revised form 23 July 2004; accepted 25 July 2004 Abstract A prospective study was designed to investigate the presence of Neospora caninum in semen and blood of eight bulls seropositive to N. caninum using nested-PCR procedures. Positive semen and blood samples were bioassayed in a BALB/c nu/nu mouse model. Specific anti-N. caninum serological and interferon-gamma (IFN-g) responses were also studied. In parallel, five seronegative bulls acted as non-infected controls. All bulls were located in a collaborating AI centre and monitored for 22 weeks. Six of eight seropositive bulls showed N. caninum DNA in their semen and/or blood samples at some time during the course of the study. In all positive semen samples, we consistently found Neospora-DNA in the cell fraction and not in seminal plasma. Parasite load, as determined by a real-time PCR in nested-PCR positive semen samples, ranged from 1 to 10 parasites/ml. We found no association between the presence of N. caninum DNA in semen and blood. N. caninum could not be detected in the BALB/c nu/nu mice inoculated with PCR-positive semen or blood samples. Specific IgG antibody levels in seropositive bulls fluctuated over time, at times falling below cut-off level. www.journals.elsevierhealth.com/periodicals/the Theriogenology 63 (2005) 1504–1518 * Corresponding author. Tel.: +34 91 3944069; fax: +34 91 3943908. E-mail address: luis.ortega@vet.ucm.es (L.M. Ortega-Mora). 0093-691X/$ – see front matter # 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.theriogenology.2004.07.002