Abstract:
Runting-Stunting Syndrome (RSS) is a transmissible disease associated with different enteric viruses in poultry worldwide. This syndrome causes considerable economic losses due to hatchery condemnations, poor feed conversion, decreased body weight and poor uniformity at slaughter. In Nigeria, these conditions are common in commercial poultry production but little is known about the role of enteric viruses in their aetiology. The presence of enteric viruses [Chicken Astrovirus (CAstV), Avian Nephritis Virus (ANV), Turkey Astroviruses (TAstV-1 and TAstV-2), Avian Reovirus (ARV), Avian Rotavirus (AvRV), Chicken Parvovirus (ChPV) and Fowl Adenovirus (FAdV)] was therefore investigated in commercial broilers and turkeys with RSS in Ogun, Osun and Oyo States, Nigeria.
Using purposive sampling method, 261 blood and intestinal content samples each were collected between November, 2017 and April, 2018 from 158 Day-Old Chicks (DOCs), six 14-week-old chickens and 97 turkey poults. The birds comprised 164 commercial broilers (Ogun 67, Osun 20, Oyo 77) and 97 turkeys (Osun 14, Oyo 83) with signs of RSS from poultry farms (n=10) and hatcheries (n=6). Sera were screened for CAstV and ANV antibodies using immunofluorescence assay. Suspensions (10%) of intestinal contents in phosphate buffered saline were processed for virus isolation in chicken embryo liver cells and identified by Electron Microscopy (EM). Detection and quantification of viral nucleic acid was performed by conventional and real-time Polymerase Chain Reaction (PCR) or Reverse Transcriptase-PCR (RT-PCR). Amplicons obtained were sequenced bi-directionally and phylogenetic analysis was performed with a software. Data were analysed using one-way ANOVA (α0.05).
Seropositivity was 7.9% and 3.1% for CAstV in broilers and turkeys, respectively but 0% for ANV in both. Four isolates were obtained: three confirmed as FAdV in DOCs by EM and conventional PCR, and one as ARV by RT-PCR in 14-week-old chickens. Real-time RT-PCR and PCR assays detected CAstV RNA (log10 2.2-8.0) in 100.0% (164/164), ANV RNA (log10 2.8-4.9) in 4.9% (8/164) and ChPV DNA (log10 2.6-3.2) in 3.7% (6/164) of chickens sampled. Five DOCs and all 14-week-old chickens were positive for both CAstV and ANV. In turkeys, 81 out of 97 were positive for CAstV RNA (log10 2.3- 6.2). All the samples tested negative for AvRV, TAstV-1 and TAstV-2. Multiple alignment of CAstV nucleotide sequences showed high similarity (98.0-100.0%), while phylogenetic analysis revealed they belonged to CAstV Bi clade. Furthermore, ANV (80.0% homology with ANV-2 strain), ARV (83.0% homology with a German strain), ChPV (95.0% identity with enteric parvoviruses) and FAdVs (99.0% and 97.0% identities with serotypes 4 and 5, respectively) were identified.
The association of enteric viruses with runting-stunting syndrome in southwestern Nigeria was established. High detection rate of group Bi CAstV and low occurrence of ANV, ARV, ChPV and FAdV suggested that CAstV was strongly associated with hatchery condemnations and runting-stunting syndrome in commercial broilers and turkeys. Vaccination of commercial breeder birds to prevent vertical transmission of these viruses is recommended.
