Most of the cats were captured using baited traps; others being caught directly in their owner's houses. Upon capture, cats were anaesthetized with an intramuscular injection of ketamin chlorhydrate (Immalgène 1000 15 mg/kg, Rhône-Mérieux) and acepromazin (Vétranquil 5.5% 0.5 mg/kg, Sanofi). They were marked permanently using an electronic passive integrative transponder (pig-tag) to allow all individuals to be identified in case of recapture. For each cat, we have recorded, among other data, information on sex, age and serological status in relation to FIV. Blood samples were taken from the jugular vein and the cats were then released. The ELISA method (SNAP Combo +, Idexx) was used to detect the presence of FIV-specific antibodies, which generally identifies virus carriers [6] . All positive sera for FIV were confirmed by Western blot analysis [21] . FIV was scored as present or absent for each sampled cat.