Adeno-like Virus in Esophageal and Tracheal Mucosa of a Jackson's Chameleon (Chamaeleo jacksoni)

Abstract

Members of the family Adenoviridae are DNA viruses that range in size from 65 to 80 nm in diameter and undergo multiplication in the nucleus. In reptiles, adeno-like viral infections have been reported in Nile crocodiles, snakes, and lizard^.^ Here, we report on adeno-like viral particles in esophageal and tracheal mucosal epithelial cells of a Jackson’s Chameleon, Chamaeleo jacksoni. A 6-month-old, 15-gram, Jackson’s Chameleon died 3 days after becoming anorexic. One and one-half days prior to death, it manifested opisthotonos. The lizard was born in a private collection in Gainesville, Florida, and had ten litter mates. Of six siblings that were sold, two died; necropsies were not performed. The dead lizard was necropsied, and multiple tissues including all major organ systems and brain were fixed in 10% neutral buffered formalin, embedded in paraffin, sectioned at 7 pm, and stained with hematoxylin and eosin. Sections of trachea and esophagus were also stained by the Feulgen method. A section of paraffin-embedded esophagus was deparaffinized, then fixed in Dalton’s osmium dichromate solution and embedded in polaron 8 12 (Polarbed, Micro Structure, Pty, Ltd., London, England). Thick sections were stained with toluidine blue and examined by light microscopy. Ultrathin sections were placed on copper grids, stained with uranyl acetate and lead citrate, and examined with an electron microscope. At necropsy, no gross abnormalities were seen. Histologic examination of the trachea and esophagus revealed a proliferation of the mucosal epithelial lining. In some areas the tracheal and esophageal mucosa was up to six cells thick (Fig. l), and epithelial cells near the basement membrane were vacuolated. Small mononuclear inflammatory cells were scattered throughout. In the proliferative areas of both the esophageal and tracheal mucosa, hematoxylin and eosin staining revealed eosinophilic intranuclear inclusions within many of the ciliated epithelial cells (Fig. 2). The inclusions stained red (positively) with the Feulgen technique for nucleic acid. With electron microscopy, inclusion-bearing epithelial cells were found to contain numerous viral-like particles. In some nuclei, particles formed crystalline arrays (Fig. 3). Particles had hexagonal outlines, measured 60 to 65 mm, and had both electron-dense and electron-lucent cores (Fig. 4). In this chameleon, intranuclear inclusions were found in ciliated epithelial cells of the mucosa of esophagus and trachea. In most reptiles, both the esophageal and tracheal mucosa consist of either simple or pseudostratified cuboidal to columnar secretory and ciliated epithelial This differs from mammals whose esophageal mucosa is lined by a squamous epithelium. The presence of intranuclear inclusions in this case suggests a viral infection. While herpesviruses typically produce eosinophilic intranuclear inclusions and those of adenoviruses are often basophilic, I tinctorial exceptions have been reported. The herpesvirus of green turtle gray patch disease forms amphophilic to lightly basophilic intranuclear inclusions,8 and in human adenoviral types 1, 2, and 5 (Group C) infections, the inclusions that initially form are eosinophiliq2 further, nonviral eosinophilic intranuclear inclusions have also been reported in reptile^.^ Electron microscopy revealed that the inclusions in this chameleon were viral in nature. The location and electron microscopic appearance of the particles were compatible with those seen with viruses of the families Adenoviridae and Herpesviridae. As part of maturation, herpesviruses typically undergo envelopment from the nuclear membrane, while adenoviruses are unenveloped. I Envelopment of viral particles from the nuclear membrane was not seen in this chameleon. While capsides of herpesviruses range from 85 to 110 mm in diameter, those of adenoviruses range from 65 to 80 nm in diameter.I.’ Even if we account for a 20% reduction in ,size of particles due to processing9 the particles in the chameleon are in the size range for the latter group of viruses. Based on these findings, the particles seen in the chameleon were most compatible with those of the family Adenoviridae.