A rapid method for identifying the thymidine kinase genes of avipoxviruses

Characterization of Fowlpox Virus

The complex cytoplasmic DNA virus known as the fowlpox virus (FWPV) is a member of the avipoxvirus genus, Subfamily Chordopoxvirinae, and Family Poxviridae. The large genome size of FWPV makes it a potential vector for the creation of vaccines against a range of serious veterinary and human ailments. It also allows for multiple gene insertion and the generation of abortive infection in mammalian cells. The virus, which causes fowlpox in chickens and turkeys, is mainly transmitted to poultry through aerosols or biting insects. Fowlpox is a highly contagious disease that affects both domestic and wild birds, causing cutaneous and/or diphtheritic illnesses. To control the illness, strict hygiene practices and immunization with FWPV attenuated strains or antigenically similar pigeon pox virus vaccines are employed. Recent years have seen an increase in fowlpox outbreaks in chicken flocks, primarily due to the introduction of novel forms of FWPV. It is believed that the pathogenic characteristics of these strains are enhanced by the integration of reticuloendotheliosis virus sequences of variable lengths into the FWPV genome. The standard laboratory diagnosis of FPV involves histopathological analysis, electron microscopy, virus isolation on chorioallantoic membrane (CAM) of embryonated chicken eggs or cell cultures, and serologic techniques. For quick and consistent diagnosis, polymerase chain reaction (PCR) has proven to be the most sensitive method. PCR is used in concert with restriction endonuclease enzyme analysis (REA) to identify, differentiate, and characterize the molecular makeup of isolates of the fowlpox virus. Sequencing of the amplified fragments is then done.

The Development of Methods for the Production of New Molecular Vaccines and Appropriate RNA Fragments to Counteract Unwanted Genes: A Pilot Study

The potential of viruses as appropriate vectors for the development of new therapeutic strategies, as well as for the design of molecular (DNA, RNA, and/or protein) vaccines via substitution of nucleotide sequences, has been proven. Among the most appropriate DNA and/or RNA fragments, members belonging to families Parvoviridae (particularly adeno-associated virus, AAV) and Poxviridae have frequently been suggested for this purpose. In previous studies, the vaccine avipoxvirus strains FK (fowl) and Dessau (pigeon) have been proven able to infect mammalian cells (as well as avian cells), and to replicate productively in a small number of them; thus, we may be able to adapt them using incubation, and in these conditions. Additionally, we have previously proved, based on AAV recombinant DNA vectors, that it is possible to transfer appropriate genes of interest via mouse embryonic stem cells (mESCs). In the current study, we develop methods for the application of the same vaccine avipoxviral strains, based on the AAV DNA genome recombinant constructs, to be used for gene transfer in cells, for the transfer of DNA and/or RNA fragments (for the suppression of unwanted viral and/or cellular genes), and for the production of molecular (DNA, RNA, and/or protein) anti-cancer and anti-viral vaccines. To this end, sub-populations of embryonic mammalian cells infected with the two forms of both vaccine avipoxviral strains were frozen in the presence of cryo-protector dimethylsulfoxide (DMSO), subsequently thawed, and re-incubated. In most cases, the titers of the intra-cellular forms of the two strains were higher than those of their extra-cellular forms. These data were explained by the probable existence of the intra-cellular forms as different sub-forms, including those integrated in the cellular genome proviruses at a given stage of the cellular infection, and suggest the possibility of transferring nucleotide (DNA and/or RNA) fragments between cellular and viral genomes; this is due to the influence of activated fusion processes on DMSO, as well as drastic temperature variations.

Avipoxviruses: infection biology and their use as vaccine vectors

Avipoxviruses (APVs) belong to the Chordopoxvirinae subfamily of the Poxviridae family. APVs are distributed worldwide and cause disease in domestic, pet and wild birds of many species. APVs are transmitted by aerosols and biting insects, particularly mosquitoes and arthropods and are usually named after the bird species from which they were originally isolated. The virus species Fowlpox virus (FWPV) causes disease in poultry and associated mortality is usually low, but in flocks under stress (other diseases, high production) mortality can reach up to 50%. APVs are also major players in viral vaccine vector development for diseases in human and veterinary medicine. Abortive infection in mammalian cells (no production of progeny viruses) and their ability to accommodate multiple gene inserts are some of the characteristics that make APVs promising vaccine vectors. Although abortive infection in mammalian cells conceivably represents a major vaccine bio-safety advantage, molecular mechanisms restricting APVs to certain hosts are not yet fully understood. This review summarizes the current knowledge relating to APVs, including classification, morphogenesis, host-virus interactions, diagnostics and disease, and also highlights the use of APVs as recombinant vaccine vectors.

Identification and nucleotide sequence of the thymidine kinase gene of swinepox virus

Using degenerative oligonucleotide probes, representing two different conserved regions of poxvirus and mammalian thymidine kinase (TK) genes, the swinepox virus (SPV) TK gene was mapped to a 1.7-kb BamHI-HindIII fragment of the viral genome. Nucleotide sequencing of this DNA piece revealed that the SPV TK gene was encoded by an open reading frame (ORF) of 177 codons. Immediately downstream of the TK gene was a second ORF with homologues at the same location in both capripoxvirus and leporipoxvirus genomes. A similar gene had translocated to near the left hand terminus of the vaccinia virus (orthopoxvirus) genome. Flanking the two SPV genes were ORFs whose counterparts in other poxvirus genera are located at the same relative positions. SPV appeared to be most closely related to capripoxvirus, based on the organization of the four genes and on the percentage of identical amino acid residues of the respective encoded proteins.

Expression and characterization of the thymidine kinase gene of African swine fever virus

The thymidine kinase (TK) gene of African swine fever virus (ASFV) was located within the viral genome by using two degenerate oligonucleotide probes derived from sequences of the vaccinia virus and cellular TK genes. The TK gene was mapped within a 0.72-kbp BglII-XhoI fragment (0.242 to 0.246 map units) derived from a 23.9-kbp SalI-B fragment of the ASFV genome. Identification of this region as the ASFV TK gene was confirmed by expression of TK in Escherichia coli and by the synthesis of active TK in a cell-free system programmed with RNA synthesized in vitro. The sequenced gene for TK includes an open reading frame of 588 nucleotides encoding a protein of 196 amino acids. The deduced amino acid sequence shows 32.4% identity with the TK of vaccinia virus.

Genetic and antigenic differences between fowlpox and quailpox viruses

The genomes of a fowlpox and quailpox virus isolate were compared by restriction enzyme analysis using BamHI, EcoRI, and HindIII endonucleases. The genetic profiles of the two virus species were very distinct with fragments lacking similar electrophoretic mobilities. In contrast, the patterns of three quailpox virus isolates were very similar with a high proportion of co-migrating fragments. When the immunogenic proteins of two quailpox, three fowlpox, a juncopox, and a pigeonpox virus isolate were examined by immunoblotting, common as well as unique antigens were detected. The greatest disparity was between quailpox virus and the other three species which are genomically conserved. Therefore, on the basis of genetic as well as immunological analysis, quailpox virus is a distinct species of the genus Avipoxvirus.