Abstract
Viral metagenomic analysis of the liver of a black headed python (Aspidites melanocephalus) euthanized for a proliferative spinal lesion of unknown etiology yielded the first characterized genome of a reptile-infecting circovirus (black-headed python circovirus or BhPyCV). BhPyCV-specific in situ hybridization (ISH) showed that viral nucleic acids were strongly expressed in the intestinal lining and mucosa and multifocally in the liver. To investigate the presence of this virus in other snakes and its possible pathogenicity, 17 snakes in the python family with spinal disease were screened with ISH yielding a second BhP positive in intestinal tissue, and a Boelen’s python (Morelia boeleni) positive in the liver. BhPyCV specific PCR was used to screen available frozen tissues from 13 of these pythons, four additional deceased pythons with and without spinal disease, and fecal samples from 37 live snakes of multiple species with unknown disease status. PCR detected multiple positive tissues in both of the ISH positive BhP and in the feces of another two live BhP and two live annulated tree boas (Corallus annulatus). Preliminary analysis indicates this circovirus can infect BhPs where it was found in 4/5 BhPs tested (2/2 with spinal disease, 2/3 live with unknown status), Boelen’s python (1/2 with spinal disease), and annulated tree boa (2/6 live with unknown status) but was not detected in other python species with the same spinal lesions. This circovirus’ causal or contributory role in spinal disease remains speculative and not well supported by these initial data.
Highlights
Circoviruses have some of the smallest viral genomes ranging in size from 1.7 to 2.1 kb of circular ssDNA encoding two major proteins, the replication-associated protein (Rep) involved in genome replication and the nucleocapsid (Cap) [1]
Circovirus pathogenicity is linked to opportunistic secondary infections and has been studied most extensively in pigs infected with porcine circovirus type 2 (PCV2) [11] and in birds infected with Psittacine beak and feather disease virus (BFDV) [12]
An origin of replication consisting of a 9 base-pair stem-loop topped by unpaired canonical TAGTATTAC sequence was flanked by a Rep protein open reading frame (ORF) encoded on the same strand and a Cap protein ORF encoded on the complementary strand (Figure 1A)
Summary
Circoviruses have some of the smallest viral genomes ranging in size from 1.7 to 2.1 kb of circular ssDNA encoding two major proteins, the replication-associated protein (Rep) involved in genome replication and the nucleocapsid (Cap) [1]. Most notorious for causing diseases of birds and swine, circovirus infections have been documented in other species of mammals, and more recently in amphibians and fish [2,3,4,5]. Endogenized sections of circovirus genomes have been detected in the germ line of mammals, birds, amphibian, reptiles, hagfish, bony fish, and in seven species of snakes in the Viperidae family and one member of the Pythonidae family (Burmese python or Python bivittatus) [6, 7]. Circoviruses cause diseases of the immune system, with lymphoid necrosis and depletion in primary or secondary lymphoid tissues linked with immunosuppression [9, 10]. Other circoviruses with described disease associations include canine circovirus [16,17,18], mink circovirus and other avian circoviruses [12, 19, 20]
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