Avipoxvirus outbreak in cutaneous lesions of the red-cowled cardinal (Paroaria dominicana) and red-crested cardinal (Paroaria coronata): detection by histopathology and transmission electron microscopy

The red-cowled cardinal (Paroaria dominicana) and red-crested cardinal (Paroaria coronata) are birds of the family Emberizidae naturally found in northeastern and southern Brazil, respectively. These species are targeted by illegal trade because of their colorful plumage and are considered potential viral reservoirs owing to their migratory characteristics. Avian pox is a highly infectious disease caused by poxviruses of the family Poxviridae and genus Avipoxvirus that affects domestic and wild birds. Between January 2006 and September 2007, 72 birds, including 14 red-crested cardinals and 58 red-cowled cardinals, were referred after sudden death by CRAS-PET to the Electron Microscopy Laboratory of the Biological Institute of São Paulo for investigation of viral agents. At necropsy, small cutaneous nodular lesions were observed on the feet of one red-crested cardinal and ten red-cowled cardinals. Some birds had lesions characteristic of avian pox on the feet and/or beaks, consisting of whitish or yellowish nodules and desquamating crusts. Lesion fragments were processed for histopathology and transmission electron microscopy. Light microscopy revealed hyperkeratosis, epithelial hyperplasia, hydropic degeneration, and eosinophilic inclusions corresponding to Bollinger bodies in skin and/or mucosal cells. Negative staining identified numerous typical poxvirus particles in ten crust-suspension samples from red-cowled cardinals and one from a red-crested cardinal. Some particles were enveloped and brick-shaped, with irregularly arranged tubules on the outer membrane, and measured 280 × 260 nm. Ultrathin sections revealed type A intracytoplasmic inclusion bodies, or Bollinger bodies, containing mature or complete oval viral particles measuring 330 × 260 nm, with a biconcave nucleus or dumbbell-shaped internal core. Type B inclusion bodies, immature particles budding from dense amorphous filamentous material, developing particles with spikes on their outer surface, fibrillar inclusions, and deformed nuclei with densely condensed chromatin were also identified. Immunocytochemistry with colloidal gold labeled viral particles and antigenic sites in intracytoplasmic vacuoles and cellular debris. This is the first record of avian pox in the red-crested cardinal (Paroaria coronata) and the second in the red-cowled cardinal (Paroaria dominicana).