Liao ning virus in China
© Lu et al; licensee BioMed Central Ltd. 2011
Received: 12 April 2011
Accepted: 8 June 2011
Published: 8 June 2011
Liao ning virus is in the genus Seadornavirus within the family Reoviridae and has a genome composed of 12 segments of double-stranded RNA (dsRNA). It is transmitted by mosquitoes and only isolated in China to date and it is the only species within the genus Seadornavirus which was reported to have been propagated in mammalian cell lines. In the study, we report 41 new isolates from northern and southern Xinjiang Uygur autonomous region in China and describe the phylogenetic relationships among all 46 Chinese LNV isolates.
The phylogenetic analysis indicated that all the isolates evaluated in this study can be divided into 3 different groups that appear to be related to geographic origin based on partial nucleotide sequence of the 10th segment which is predicted to encode outer coat proteins of LNV. Bayesian coalescent analysis estimated the date of the most recent common ancestor for the current Chinese LNV isolates to be 318 (with a 95% confidence interval of 30-719) and the estimated evolutionary rates is 1.993 × 10-3 substitutions per site per year.
The results indicated that LNV may be an emerging virus at a stage that evaluated rapidly and has been widely distributed in the north part of China.
Liao ning virus (LNV) which is the member within the genus Seadornavirus family Reoviridae was composed of 12 double-stranded RNA (dsRNA). The Seadornaviruses include three species, Banna virus (BAV), Kadipiro virus (KDV) and LNV . BAV was initially isolated from patients with encephalitis and appears to be pathogenic to humans . Though there have been no confirmed reports of human disease due to LNV, this virus replicates in mammalian cells and causes viraemia and haemorrhage in mice , suggesting LNV may be pathogenic to humans or animals . Recently, LNV isolates from mosquitoes have been obtained from several regions in north China [3–5]. Here, we report additional isolates from northern and southern Xinjiang province and describe the phylogenetic relationships among Chinese LNV isolates.
The MrModeltest version 2.3 http://www.softpedia.com/get/Science-CAD/MrModeltest.shtml software program was used to examine 24 models of nucleotide substitution to determine the model most appropriate for Bayesian coalescent analysis of the LNV dataset. The general time reversible evolutionary model incorporating a gamma distribution (GTR + G) was found according to the Akaike information criterion. Both strict and relaxed (uncorrelated exponential and lognormal) molecular clocks  were employed to explore and the relaxed-uncorrelated lognormal molecular clock was the best supported model, according to the estimated Bayes factor using the TRACER program. Preliminary analyses revealed that the population dynamics of LNVs supported a model of Bayesian skyline models . The dataset was examined with Bayesian Markov chain Monte Carlo (MCMC) methods implemented in the BEAST package using a chain length of 100,000,000 generations with 10% removed as burn- in. All runs were checked for convergence by using the TRACER program http://tree.bio.ed.ac.uk/software/tracer/. The rate of nucleotide substitutions per site per year and the date of the time of most common ancestor (TMRCA) for these viruses were estimated. Maximum clade credibility (MCC) tree was constructed and converted to a graphics format using Figtree software version 1.2.2 http://tree.bio.ed.ac.uk/software/figtree/.
Information of LNV isolates in China
Time of Collection
Kashi, southern Xinjiang
XJ0602, XJ0603, XJ0606, XJ0610, XJ0611, XJ0614, XJ0615, XJ0616, XJ0620, XJ0621, XJ0623, XJ0624, XJ0626, XJ0627, XJ0632, XJ0635, XJ0640, XJ0642, XJ0648, XJ0653, XJ0654, XJ0656, XJ0657, XJ0658, XJ0659, XJ0661, XJ0662, XJ0665, XJ0670, XJ0672, XJ06121
Bayinguoleng, southern Xinjiang
XJ0719, XJ0727, XJ0735, XJ0737
XJ0740, XJ0746, XJ0753
Alertai, northern Xinjiang
Culex pipiens pallens
Arbovirus undergoes substantially slower rates of evolution . For example, the evolution rates of Dengue virus and bluetongue virus are about 10-4[9, 10]. Our results showed that the evolution rate of LNV was 1.993 × 10-3 which is faster than other arbovirus. In addition, the TMRAC of LNV was estimated to be 381 years, indicating LNV is an emerging virus and at a stage that evaluated rapidly to accommodate the host and the environment now. Also, the nucleotide and amino acid homology rate showed high identity within each group and much divergent between the groups. The geographical characteristic implies that LNV could raise natural circle in the locality though the diverged time of each group was quite recent.
In recent years, arbovirus surveillances have been done in many provinces. Japanese encephalitis virus, Tahyna virus, Getah virus and other arboviruses were isolated nationwide [11–13]. But all of the LNV isolates have been obtained only in region extending from Latitude 36°N to 47°N in the northwest to northeast part of the country. So for what reason, the virus has only been isolated from such a narrow geographic is too be studied.
LNV seemed to be at a stage of evolving rapidly than most of the arbovirus. Also it is much divergent between each subtype. Can such virus genetic differences have pathogenicity differences? LNV is pathogenic to mice, and seasonal encephalitis in the absence of Japanese encephalitis occurs in the areas where LNV is found in China [14, 15], future research should investigate the potential association of LNV and human diseases.
This work was supported by grants from the Ministry of Science and Technology of China (no. 2008ZX10004-001), China CDC-US CDC Cooperative Agreement U19-GH000004, The Young Scholar Scientific Research Foundation of China CDC (no.2010A105) and Development Grant of State Key Laboratory for Infectious Disease Prevention and Control (2008SKLID105). The authors thank Dr. Roger S. Nasci of the U.S. Centers for Disease Control and Prevention for consultation and assistance in the preparation and writing of this manuscript.
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