The selection of organs to be examined for biodistribution analyses followed the applicable European and international guidelines (EMEA 1995 (EMEA , 2000 WHO 2005) . For biodistribution analyses, tissue samples (3×3×3 mm 3 ) were dissected out, rinsed with cold phosphate-buffered saline (PBS) and snap-frozen in cryotubes in liquid nitrogen. For shedding analyses, selected excretions and biological fluids (i.e., semen [only for groups 7 and 8], serum, urine, throat and nasal swabs, saliva, vaginal secretion and faeces) and PBMC were collected. Throat swabs, saliva, nasal secretions and vaginal secretions were conserved in M4RT tubes (Remel, Oxoid, Cedex, France) at −70°C. Semen and faeces were directly frozen in cryotubes and conserved at −70°C. Immediately after collection, urine was centrifuged (800×g, 10 min, 4°C) and the pellet was resuspended in PBS and stored at −70°C. PBMC were isolated from EDTA blood samples by gradient centrifugation and frozen in PBS (−70°C). To obtain serum, blood was collected in plain tubes, incubated (20 min, room temperature) and centrifuged (3,000×g, 10 min, 4°C).