Feeding Cyprinus carpio with infectious materials mediates cyprinid herpesvirus 3 entry through infection of pharyngeal periodontal mucosa

The Cyprinid herpesvirus 3 (CyHV-3; species Cyprinid herpesvirus 3, genus Cyprinivirus, family Alloherpesviridae, order Herpesvirales), also known as koi herpesvirus, is the aetiological agent of a contagious and mortal disease in common (Cyprinus carpio carpio) and koi (Cyprinus carpio koi) carp [1-5]. Since its emergence, in the late 1990s, CyHV-3 has caused severe economic losses in both common and koi carp culture industries worldwide [4,6,7].The recent publication of the CyHV-3 sequence [8], together with the cloning of its genome as an infectious bacterial artificial chromosome (BAC) [9], allowed the production of CyHV-3 recombinant strains. Recently, we took advantage of these advances to construct a luciferase (LUC)-expressing recombinant strain by intergenic insertion of a LUC expression cassette [10]. Using this recombinant strain, bioluminescent imaging, and an original system to perform percutaneous infection restricted to the posterior part of the fish, we showed that the skin covering the fins and the body, and not the gills, is the major portal of entry after inoculation by immersion in water containing the virus [10]. This study, together with an earlier report addressing the portal of entry of a rhabdovirus (infectious hematopoietic necrosis virus) in salmonids [11], suggests that the skin of teleost fish is an efficient portal of entry for certain viruses.The skin is the major portal of entry of CyHV-3 in carp after inoculation by immersion in water containing the virus [10]. While this model of infection certainly mimics some natural condition of infections, other conditions could favor entry of the virus through the digestive tract. Firstly, droppings from infected carp have been shown to contain infectious virus [12]. Ingestion of infectious droppings or food contaminated by droppings by na？ve subjects could represent a source of oral inoculation. Secondly, carp express cannibalistic and necrophagous behaviour. By ingestion of infectious tissues