Interactions between avian viruses and skin in farm birds

Abstract

This article reviews the avian viruses that infect the skin of domestic farm birds of primary economic importance: chicken, duck, turkey, and goose. Many avian viruses (e.g., poxviruses, herpesviruses, Influenza viruses, retroviruses) leading to pathologies infect the skin and the appendages of these birds. Some of these viruses (e.g., Marek's disease virus, avian influenza viruses) have had and/or still have a devasting impact on the poultry economy. The skin tropism of these viruses is key to the pathology and virus life cycle, in particular for virus entry, shedding, and/or transmission. In addition, for some emergent arboviruses, such as flaviviruses, the skin is often the entry gate of the virus after mosquito bites, whether or not the host develops symptoms (e.g., West Nile virus). Various avian skin models, from primary cells to three-dimensional models, are currently available to better understand virus-skin interactions (such as replication, pathogenesis, cell response, and co-infection). These models may be key to finding solutions to prevent or halt viral infection in poultry.

Keywords: Avian viruses; chicken; duck; feathers; in vitro skin models; keratinocytes; skin tropism.

Figure 1

Structure of the avian skin. Skin is constituted by an epidermis and a dermis separated by the basement membrane. Three layers constitute bird’s epidermis: the basal layer made of undifferentiated basal keratinocytes, the intermediate layer and the cornified layer made of cornified keratinocytes that are fully differentiated. Keratinocytes are rich in lipids and/or lipid droplets. The dermis is a fibrous vascularized structure mainly composed of fibroblasts and of matrix components such as collagen fibers. By analogy to mammals, it is probable that dendritic cells and T-lymphocytes also reside in the dermis. Langerhans cells are present in basal but also intermediate layers of the epidermis. This figure was illustrated by using BioRender.com (Agreement number: XJ26EG35BS).

Figure 2

Hard and soft skin appendages in birds/chicken. On the left panel, soft skin appendages including comb, eyelids, maxillary rictus, earlobes and wattles are shown. On the right panel, hard skin appendages including beak, feathers, feather follicles and chicken legs skin are shown with a special focus onto legs scales. Legs possess different hard cornified elements: claw, scutate scales (large and distally overlapping scales) onto digits and anterior face of the shank, scutella scales (smaller and proximally overlapping scales) on the posterior face of the shank and finally reticulate scales (smaller) that recover the remainder of foot surface and are non-overlapping. This figure was illustrated by using BioRender.com (Agreement number: GC26L9TWNH) and Inkscape software.