Molecular characterisation and pathogenicity of chicken astrovirus isolated from commercial broiler chickens in Malaysia
Chicken astrovirus (CAstV) is a ubiquitous enteric RNA virus that has been associated mainly with conditions including runting stunting syndrome, kidney and visceral gout, and white chick syndrome in broiler-type of chickens across the globe. In Malaysia, the detection of the virus amongst broil...
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| Format: | Thesis |
| Language: | English |
| Published: |
2021
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/105908/1/RAJI%20ABDULLAHI%20ABDULLAHI%20-%20IR.pdf |
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| Summary: | Chicken astrovirus (CAstV) is a ubiquitous enteric RNA virus that has been
associated mainly with conditions including runting stunting syndrome,
kidney and visceral gout, and white chick syndrome in broiler-type of
chickens across the globe. In Malaysia, the detection of the virus amongst
broiler flocks has not been studied. The description of CAstV in this chapter
is based on an RT-PCR assay, serology, genome characteristics and
pathogenicity of the virus in specific-pathogen-free (SPF) chickens. The
viruses were detected from tissue broiler chickens suffering from kidney
disease and poor performance. A total of 20 tissue samples obtained from
different broiler flocks between 2017 and 2018 were confirmed positive for
CAstV based on polymerase gene (ORF1b) specific RT-PCR detection. A
serological study based on CAstV group B enzyme-linked immunosorbent
assay (ELISA) revealed a high incidence of the virus amongst broilerbreeder
flocks. The tissue samples were then used to isolate CAstV using 5-
day-old SPF embryonated chicken eggs (ECE). After four passages, only
three isolates, IBS503/2017, IBS543/2017 and UPM1019/2018 were isolated
and considered for further studies.
Three pairs of overlapping primer sets were designed to amplify a nearly
complete genome sequence of the three CAstV that were propagated in
SPF-ECE. The amplicons were sequenced on the Illumina MiSeq platform.
The generated raw sequencing data were transferred and de novo assembled
in a genome assembly software for consensus generation and mapping to
reference. The analysis produced a near-complete genome sequence of the
three CAstV isolates IBS503/2017, IBS543/2017 and UPM1019/2018 with the genome length of 7424bp, 7379bp and 7397bp, respectively. The
genomic organisation of the three isolates exhibited three open reading
frames, ORF-1a, ORF-1b, and ORF-2, that encode for trypsin-like serine
protease, RNA-dependent RNA polymerase (RdRp) and capsid protein,
respectively. A point mutation of guanine (G) to thymine (T) was observed
in the spacer sequence between ORF-1a and ORF-1b. Additionally, a third
stem-loop like motif (s2m) was observed at the 3’-end of the untranslated
region (UTR). Genome analysis of the isolates at the nucleotide level with
other CAstV genomes showed a similarity of 77% with group B CAstV
from China, 87% with group B Indian strain, 88 to 89% with group B North
American strains, and 74% similarity with group A CAstV from Poland.
However, analysis based on the capsid gene sequences classified the
isolated viruses as group B CAstV, showing a sequence similarity at the
nucleotide level (91.96 to 93.78%) and amino acid (90.51 to 93.63%) with
CAstV isolates in subgroup Bi, Biii and Biv. Sequence similarity of 76.18 to
90.09% and 86.02 to 89.97% at nucleotide and amino acid levels,
respectively, were observed between the three Malaysian isolates and
subgroup Bii. Interestingly, phylogenetic analysis indicated the three
Malaysian isolates were clustered and formed a new subgroup, tentatively
subgroup Bv.
Pathogenicity study of one of the isolates, UPM1019/2018 on one-day-old
SPF chickens, produced clinical manifestations related to CAstV infection.
However, no mortality was recorded throughout the study. Diarrhoea and
somnolence were the most observed clinical signs accompanied by
decreased feed intake in both the challenged and exposed sentinel groups.
Dehydration, cachexia, ballooned intestines were observed on post-mortem
examinations. Three birds (two from the challenged group and one from
the exposed sentinel group) exhibiting enlarged kidneys and ureters with
urate deposits and visceral gout were observed on days 6 and 9 postinoculation.
Microscopically, the observable lesions were mild lymphocytic
aggregates in the duodenum, tubular degeneration and interstitial
nephritis. Real-time RT-PCR assay detected CAstV RNA from the cloacal
swabs of both the challenged and exposed sentinel groups throughout the
study. The highest mean virus copy number (log10 13.23) was on day 3
post-inoculation in the challenged group. In contrast, the exposed sentinel
group has a peak mean virus copy number (log10 9.04) on day 6 postinoculation.
In conclusion, the isolated Malaysian CAstV is pathogenic in SPF chickens,
causing lesions in the gut and kidneys in both the infected and exposed
chickens. Although the studied CAstV are classified under group B, they
are distinct from other CAstV strains forming a new subgroup Bv. |
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