Fowlpox virus: an overview of its classification, morphology and genome, replication mechanisms, uses as vaccine vector and disease dynamics

SUMMARYFowlpox virus (FWPV) is a complex cytoplasmic DNA virus belonging to the Family- Poxviridae, Subfamily-Chordopoxvirinae and Genus-Avipoxviruses. The large size of the genome accommodates multiple gene inserts and the induction of abortive infection in mammalian cells and thus makes FWPV a promising vector for vaccine development against several important veterinary and human diseases. The virus is predominantly transmitted via aerosols or biting insects in poultry and causes fowlpox in chickens and turkeys. Fowlpox is a contagious disease of economic importance, with cutaneous and/or diphtheritic forms of infection seen in domestic and wild birds. It occurs worldwide (but is endemic in tropical and subtropical countries only) as mild to severe poultry disease. The disease is controlled via rigorous sanitation and immunisation with attenuated strains of FWPV or the antigenically similar pigeonpox virus vaccines. While most of these vaccines are highly effective in conferring long-lasting immunity, a number of recurrent outbreaks in previously vaccinated flocks have been reported. In recent years, fowlpox outbreaks in poultry flocks have been on the rise mainly due to emerging novel types of FWPV and the pathogenic traits of these strains are reportedly enhanced by integration of reticuloendotheliosis virus sequences of various lengths into the FWPV genome. This has become a hurdle in controlling the disease, thus necessitating the development of newer vaccines with improved efficacy. The present review summarises the overall dynamics of the FWPV including taxonomic classification, replication mechanisms, pathogenicity, provirus integration, its use as recombinant vaccine vector, disease impacts and diagnostics, and also highlighted gaps requiring further research.