Epidemic of cutaneous fowlpox in a naïve population of chickens and turkeys in Austria: Detailed phylogenetic analysis indicates co‐evolution of fowlpox virus with reticuloendotheliosis virus

Abstract

Cutaneous fowlpox is a disease of chickens and turkeys caused by the fowlpox virus (FWPV), characterized by the development of proliferative lesions and scabs on unfeathered areas. FWPVs regularly carry an integrated, active copy of the reticuloendotheliosis virus (REV), and it has been hypothesized that such FWPVs are more problematic in the field. Extensive outbreaks are usually observed in tropical and sub‐tropical climates, where biting insects are more difficult to control. Here, we report an epidemic of 65 cutaneous fowlpox cases in Austria in layer chickens (91% of the cases) and broiler breeders and turkeys, all of them unvaccinated against the disease, from October 2018 to February 2020. The field data revealed appearance in flocks of different sizes ranging from less than 5000 birds up to more than 20,000 animals, with the majority raised indoors in a barn system. The clinical presentation was characterized by typical epithelial lesions on the head of the affected birds, with an average decrease of 6% in egg production and an average weekly mortality of 1.2% being observed in the flocks. A real‐time multiplex polymerase chain reaction (PCR) confirmed the presence of FWPV‐REV DNA, not only in the lesions but also in the environmental dust from the poultry houses. The integration of the REV provirus into the FWPV genome was confirmed by PCR, and revealed different FWPV genome populations carrying either the REV long terminal repeats (LTRs) or the full‐length REV genome, reiterating the instability of the inserted REV. Two selected samples were fully sequenced by next generation sequencing (NGS), and the whole genome phylogenetic analysis revealed a regional clustering of the FWPV genomes. The extensive nature of these outbreaks in host populations naïve for the virus is a remarkable feature of the present report, highlighting new challenges associated with FWPV infections that need to be considered.

Current Status of Poultry Recombinant Virus Vector Vaccine Development

“…Another limitation is that vaccine and field strains of FPV can be integrated with remnants of the reticuloendotheliosis virus (REV) long terminal repeats or the near full-length genome of REV [ 74 ]. Previous studies have shown that FPV vaccine contamination with REV caused tumors in the vaccinated birds [ 75 , 76 , 77 ], and the nearly intact integrated REV provirus could likely engender infectious REV, which, consequently, may lead to immunosuppression, thereby escalating the pathogenicity [ 77 , 78 ]. However, the mechanisms involved have not been fully elucidated [ 79 , 80 ].…”

Diagnosing Infectious Diseases in Poultry Requires a Holistic Approach: A Review

“…Noteworthy is the implementation of multiplex PCR assays in i) detection of more than one pathogen in a course of a single PCR, or ii) for pathogen typing. Various assays for simultaneous detection of different pathogens have been described, such as protocols based on multiplex real-time PCR in detection of fowl poxvirus and reticuloenotheliosis virus [202,203] or detection of Mycoplasma gallisepticum and Mycoplasma synoviae [204] or conventional assays such as simultaneous detection of picorna-, astro-and caliciviruses [205] or Campylobacter, Arcobacter and Helicobacter species [206]. Similarly, diverse multiplex PCR assays are available for detecting and typing a pathogen within the same assay, and avian influenza viruses subjected to multiplex real-time PCR are a good example [207,208].…”