Phil D. Lukert

Beak and feather disease virus and porcine circovirus genomes: intermediates between the geminiviruses and plant circoviruses

SummaryCircoviruses are a diverse group of animal and plant pathogens with undefined relationships to one another but for their non-geminate, non-enveloped capsids and circular, single-stranded DNA genomes. The sequences of the beak and feather disease virus and porcine circovirus genomic DNAs are presented and analyzed in the context of the other members of the family. Sequence comparisons, inferred phylogenies, and geographic occurrence suggest that the ambisense circoviruses, particularly the beak and feather disease virus, represent an evolutionary link between the geminiviruses and the plant circoviruses. We propose that the family members be reclassified into three groups: The family Circoviridae consists of the animal pathogens (beak and feather disease virus and porcine circovirus) that possess ambisense genomes with striking similarities to the geminiviruses. The BBTV-like viruses include the plant pathogens (coconut foliar decay virus, banana bunchy top virus, subterranean clover stunt virus) with a geminivirus-like stem-loop element in their DNAs, and single to multiple component genomes. The chicken anemia virus is an unassigned virus possessing unique characteristics bearing little similarity to the other ssDNA viruses.

Characterization of a new virus from cockatoos with psittacine beak and feather disease

A novel virus isolated from the feather follicles of cockatoos diagnosed as having psittacine beak and feather disease was characterized by electron microscopy, nucleic acid content, and polypeptide composition. Purified virions displayed an icosahedral symmetry, were nonenveloped, and had a mean diameter of 14 to 16 nm negatively stained. Three major viral proteins were identified, with approximate molecular weights of 26.3, 23.7, and 15.9 kDa. The viral nucleic acid was found to be single-stranded DNA based on acridine orange staining, resistance to alkali and ribonuclease, and sensitivity to both DNAse 1 and S1 nuclease. The size of the DNA was estimated to be between 1.7 and 2.0 kb by agarose gel electrophoresis. This size and its circular conformation were confirmed by electron microscopy. A preliminary transmission study using purified virus induced pathological lesions characteristic of those observed in the natural disease. On the basis of the extremely small size of the virions and the single-stranded circular viral DNA, we propose that the etiologic agent of psittacine beak and feather disease represents a previously undescribed viral pathogen.

Comparison of three animal viruses with circular single-stranded DNA genomes.

SummaryNo common antigenic determinants and no DNA sequence homologies were detected when three animal viruses, chicken anaemia agent (CAA), porcine circovirus (PCV), and psittacine beak and feather disease virus (PBFDV), all of which possess circular single-stranded DNA genomes, were compared. Negative contrast electron microscopy showed that PCV and PBFDV particles were 30% smaller than CAA particles and lacked the surface structure of CAA.

ULTRASTRUCTURAL, PROTEIN COMPOSITION, AND ANTIGENIC COMPARISON OF PSITTACINE BEAK AND FEATHER DISEASE VIRUS PURIFIED FROM FOUR GENERA OF PSITTACINE BIRDS

Psittacine beak and feather disease (PBFD) virus, was purified from diseased tissues of a lesser sulphur-crested cockatoo (Cacatua sulphurea), a black palm cockatoo (Probosiger aterrimus), a red-lored Amazon parrot (Amazona autumnalis), and a peach-faced lovebird (Agapornis roseicollis). The histopathology of diseased feathers and follicular epithelium from the different species was compared; basophilic intranuclear inclusion bodies were identified in the follicular epithelium and intracytoplasmic globular inclusions were observed within macrophages located in the feather pulp from the four species. Psittacine beak and feather disease virus antigen was specifically detected by colloidal gold immunoelectron microscopy. The different preparations of purified virions displayed an icosahedral symmetry, were non-enveloped, and had a mean diameter that varied from 12 to 15 nm when negatively stained. Two major viral-associated proteins with approximate molecular weights of 26 and 23 kilodaltons (kd) were consistently demonstrated from the four viral preparations. Purified virions from the four genera were antigenically related. These findings suggest that the PBFD virus purified from numerous genera of diseased birds is similar based on ultrastructural characteristics, protein composition and antigenic reactivity.

Extracutaneous Viral Inclusions in Psittacine Beak and Feather Disease

Thirty-five birds that died with naturally acquired psittacine beak and feather disease (PBFD) were necropsied to identify extracutaneous viral inclusions. Inclusions were found in various tissue sections from 34 of 35 birds. By immunoperoxidase staining, intranuclear and intracytoplasmic inclusion bodies were shown to contain PBFD viral antigen. Inclusion-bearing lesions were widely disseminated but often closely associated with the alimentary tract. Lesions within the palate, esophagus, crop, intestine, bursa of Fabricius, and liver probably serve as sources for viral shedding into the feces.

A Novel DNA Virus Associated with Feather Inclusions in Psittacine Beak and Feather Disease

The nature of feather inclusions was characterized in 32 psittacine birds (30 cockatoos, one peachfaced lovebird (Agapornis roseicollis), and one red-lored Amazon parrot (Amazona autumnalis autumnalis)) with naturally-acquired psittacine beak and feather disease. Intranuclear inclusions within feather epithelial cells and intracytoplasmic inclusions within macrophages in the feather epithelium and pulp cavity contained psittacine beak and feather disease viral antigen when stained by the avidin-biotin complex immunoperoxidase technique. Ultrastructurally, inclusions were observed primarily within macrophages and to a lesser extent within epithelial cell nuclei. Macrophage inclusions appeared as paracrystalline arrays of viral particles. Intranuclear inclusions were less well defined, although scattered viral particles were present. Intracytoplasmic and intranuclear particles in ultrastructural preparations were identified by colloidal gold labeling as psittacine beak and feather disease virus. Feather epithelium was more frequently and severely involved in the disease process than was adjacent follicular epithelium. Plucked feathers with an intact epidermal collar and feather epithelium were preferred to follicular biopsies for histopathologic examination.

An inactivated avian polyomavirus vaccine is safe and immunogenic in various Psittaciformes

The safety and immunogenicity of adjuvanted and nonadjuvanted inactivated avian polyomavirus vaccines, administered either intramuscularly or subcutaneously (s.c.), were evaluated in a group of mixed species Psittaciformes. In 233 vaccinates representing species of macaws, cockatoos, conures, and parrots, gross reactions were limited to small scab formation at the s.c. injection site in three African grey parrots. Both vaccines stimulated a virus neutralizing (VN) antibody response, particularly in birds that were seronegative prior to vaccination. Ninety-three percent of the birds that were seronegative at the beginning of the study seroconverted (greater than fourfold increase in VN antibody titer) by 2 weeks after the second vaccination. Seventy-six percent of all the vaccinates had at least a fourfold increase in VN antibody titer at this time. There was no significant difference in seroconversion between the birds vaccinated with adjuvanted or nonadjuvanted vaccines. This study indicates that an inactivated avian polyomavirus vaccine can be used to safely immunize various species of psittacine birds in a field setting.