Genetic characterization of rabbit hemorrhagic disease virus from naturallyinfected rabbits in Sharkia governorate, Egypt
Genetic characterization of rabbit hemorrhagic disease virus from naturallyinfected rabbits in Sharkia governorate, Egypt
Naglaa F.S. Awad1, Gamelat K.F. Kotb2
ABSTRACT
Background: Since the first introduction of rabbit hemorrhagic disease virus (RHDV) in 1991,
Egyptian authorities started a national vaccination program against the disease. However, RHDV
clinical cases are still being reported.
Objectives: This study aimed to investigate genetic characterization of recent RHDV isolates from
naturally-infected rabbits in Sharkia governorate, Egypt in 2015/2016.
Methods: A total of 24 clinical samples were investigated by real-time reverse transcription PCR
(RRT-PCR). Hemagglutination analysis of RRT-PCR positive samples were performed, also these
positive RRT-PCR samples were purified and directly partial sequenced for C-terminal VP60 gene.
Results: Only two samples were positive for partial C-terminal VP60 amplification. The first positive
sample was collected from non-vaccinated young rabbit (45-day old) and designed here as SHAH
2015, whereas the second sample was collected from non-vaccinated adult dam (nine-month old) and
designed as SHMK2016. Hemagglutination analysis using human red blood cells type O revealed
that both isolates were non-hemagglutinating. Sequence analysis revealed that both isolates shared
amino acid identity of 98.57 % and 95.71 % with each other and with commonly used vaccinal strain
(RHDV-Giza 2006), respectively. Phylogenetic analysis revealed that both isolates clustered with
the vaccine strain and isolate UT01 within genotype 6 RHDVa. Molecular analysis of antigenic
regions of VP60 (part of E and F regions) revealed neither detection of recombination points nor sites
under positive selection.
Conclusion: The obtained results indicate that non-hemagglutinating RHDVa G6 variant viruses are
currently circulating in Sharkia with the ability to infect both young and adult rabbits that may be due
to inadequate application of vaccine and not due to vaccine mismatch. We recommend broad
application of currently applied vaccine should include both young and adult rabbits.
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January 2018
Vol. 3, Iss. 1, Pages 1-77
