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1.  Detection of Two Zoonotic Babesia microti Lineages, the Hobetsu and U.S. Lineages, in Two Sympatric Tick Species, Ixodes ovatus and Ixodes persulcatus, Respectively, in Japan 
The species Babesia microti, commonly found in rodents, demonstrates a high degree of genetic diversity. Three lineages, U.S., Kobe, and Hobetsu, are known to have zoonotic potential, but their tick vector(s) in Japan remains to be elucidated. We conducted a field investigation at Nemuro on Hokkaido Island and at Sumoto on Awaji Island, where up to two of the three lineages occur with similar frequencies in reservoirs. By flagging vegetation at these spots and surrounding areas, 4,010 ticks, comprising six species, were collected. A nested PCR that detects the 18S rRNA gene of Babesia species revealed that Ixodes ovatus and I. persulcatus alone were positive. Lineage-specific PCR for rRNA-positive samples demonstrated that I. ovatus and I. persulcatus carried, respectively, the Hobetsu and U.S. parasites. No Kobe-specific DNA was detected. Infected I. ovatus ticks were found at multiple sites, including Nemuro and Sumoto, with minimum infection rates (MIR) of ∼12.3%. However, all I. persulcatus ticks collected within the same regions, a total of 535, were negative for the Hobetsu lineage, indicating that I. ovatus, but not I. persulcatus, was the vector for the lineage. At Nemuro, U.S. lineage was detected in 2 of 139 adult I. persulcatus ticks (MIR, 1.4%), for the first time, while 48 of I. ovatus ticks were negative for that lineage. Laboratory experiments confirmed the transmission of Hobetsu and U.S. parasites to hamsters via I. ovatus and I. persulcatus, respectively. Differences in vector capacity shown by MIRs at Nemuro, where the two species were equally likely to acquire either lineage of parasite, may explain the difference in distribution of Hobetsu throughout Japan and U.S. taxa in Nemuro. These findings are of importance in the assessment of the regional risk for babesiosis in humans.
doi:10.1128/AEM.00142-12
PMCID: PMC3346458  PMID: 22389378
2.  Rift Valley Fever Virus L Protein Forms a Biologically Active Oligomer ▿  
Journal of Virology  2009;83(24):12779-12789.
Rift Valley fever virus (RVFV) (genus Phlebovirus, family Bunyaviridae) causes mosquito-borne epidemic diseases in humans and livestock. The virus carries three RNA segments, L, M, and S, of negative or ambisense polarity. L protein, an RNA-dependent RNA polymerase, encoded in the L segment, and N protein, encoded in the S segment, exert viral RNA replication and transcription. Coexpression of N, hemagglutinin (HA)-tagged L, and viral minigenome resulted in minigenome replication and transcription, a finding that demonstrated HA-tagged L was biologically active. Likewise L tagged with green fluorescent protein (GFP) was biologically competent. Coimmunoprecipitation analysis using extracts from cells coexpressing HA-tagged L and GFP-tagged L showed the formation of an L oligomer. Bimolecular fluorescence complementation analysis and coimmunoprecipitation studies demonstrated the formation of an intermolecular L-L interaction through its N-terminal and C-terminal regions and also suggested an intramolecular association between the N-terminal and C-terminal regions of L protein. A biologically inactive L mutant, in which the conserved signature SDD motif was replaced by the amino acid residues GNN, exhibited a dominant negative phenotype when coexpressed with wild-type L in the minigenome assay system. Expression of this mutant L also inhibited viral gene expression in virus-infected cells. These data provided compelling evidence for the importance of oligomerization of RVFV L protein for its polymerase activity.
doi:10.1128/JVI.01310-09
PMCID: PMC2786858  PMID: 19812169
4.  Rapid Accumulation of Virulent Rift Valley Fever Virus in Mice from an Attenuated Virus Carrying a Single Nucleotide Substitution in the M RNA 
PLoS ONE  2010;5(4):e9986.
Background
Rift Valley fever virus (RVFV), a member of the genus Phlebovirus within the family Bunyaviridae, is a negative-stranded RNA virus with a tripartite genome. RVFV is transmitted by mosquitoes and causes fever and severe hemorrhagic illness among humans, while in livestock it causes fever and high abortion rates.
Methodology/Principal Findings
Sequence analysis showed that a wild-type RVFV ZH501 preparation consisted of two major viral subpopulations, with a single nucleotide heterogeneity at nucleotide 847 of M segment (M847); one had a G residue at M847 encoding glycine in a major viral envelope Gn protein, while the other carried A residue encoding glutamic acid at the corresponding site. Two ZH501-derived viruses, rZH501-M847-G and rZH501-M847-A, carried identical genomic sequences, except that the former and the latter had G and A, respectively, at M847 were recovered by using a reverse genetics system. Intraperitoneal inoculation of rZH501-M847-A into mice caused a rapid and efficient viral accumulation in the sera, livers, spleens, kidneys and brains, and killed most of the mice within 8 days, whereas rZH501-M847-G caused low viremia titers, did not replicate as efficiently as did rZH501-M847-A in these organs, and had attenuated virulence to mice. Remarkably, as early as 2 days postinfection with rZH501-M847-G, the viruses carrying A at M847 emerged and became the major virus population thereafter, while replicating viruses retained the input A residue at M847 in rZH501-M847-A-infected mice.
Conclusions/Significance
These data demonstrated that the single nucleotide substitution in the Gn protein substantially affected the RVFV mouse virulence and that a virus population carrying the virulent viral genotype quickly emerged and became the major viral population within a few days in mice that were inoculated with the attenuated virus.
doi:10.1371/journal.pone.0009986
PMCID: PMC2848673  PMID: 20376320

Results 1-4 (4)