3.2. The feline viruses. The Feline Immunodeficiency Virus (FIV), is a major non-traumatic cause of death in adult cats, and is associated with immunosuppression causing secondary infections [64] . This retrovirus can infect other felids, most of which are threatened or endangered species e.g., the European wildcat (F. s. silvestris) [64] [65] [66] . It is mainly transmitted by bites, through a direct horizontal mode [67] , principally during aggressive or sexual contacts [64, 68] . The Feline Herpesvirus (FHV) and the Feline Calicivirus (FCV) are responsible of upper respiratory tract disease, of concern in veterinary medicine [69, 70] . Both viruses are transmitted through 'amicable' contacts, by oral, nasal and ocular secretions during close interactions [71, 72] . FHV infected cats become asymptomatic carriers, but the latent infection can be reactivated by a stress (i.e., change of habitat, lactation or fights between males; [73] ). The Feline Parvovirus (FPV) infects all felids, as well as other carnivores [74] , and FPV infection may be fatal especially in kittens [75] . The virus is transiently excreted in feces, urine, saliva and vomiting and its high resistance in the environment (still infectious after 13 months at 4-25uC; [76] ) makes indirect transmission through feces and contaminated areas largely predominant [77, 78] .