3.3. Serological data. The serological statuses for FIV, FHV, FCV and FPV were obtained in 2007 in 15 natural rural populations of domestic cats in North-Eastern France [62, 79] . Cats were captured using baited traps or directly caught by the owner, anaesthetized, measured, and blood samples were taken from the jugular vein. FIV-antibodies were immediately searched for with a commercial kit using the ELISA method (SNAP Combo +, Idexx), whereas specific antibodies against FHV, FCV or FPV were measured by a specific blocking ELISA [80] . None of the cats was vaccinated. All six pairs of viruses were tested for potential association. Between 467 and 474 cats were tested for each virus and 465 to 469 were double-tested (depending on the virus pair).