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Two Genetic Differences between Closely Related Zika Virus Strains Determine Pathogenic Outcome in Mice.

ABSTRACT: Recent Zika virus (ZIKV) outbreaks and unexpected clinical manifestations of ZIKV infection have prompted an increase in ZIKV-related research. Here, we identify two strain-specific determinants of ZIKV virulence in mice. We found that strain H/PF/2013 caused 100% lethality in Ifnar1^-/- mice, whereas PRVABC59 caused no lethality; both strains caused 100% lethality in Ifnar1 ^-/- Ifngr1 ^-/- double-knockout (DKO) mice. Deep sequencing revealed a high-frequency variant in PRVABC59 not present in H/PF/2013: a G-to-T change at nucleotide 1965 producing a Val-to-Leu substitution at position 330 of the viral envelope (E) protein. We show that the V330 variant is lethal on both virus strain backgrounds, whereas the L330 variant is attenuating only on the PRVABC59 background. These results identify a balanced polymorphism in the E protein that is sufficient to attenuate the PRVABC59 strain but not H/PF/2013. The consensus sequences of H/PF/2013 and PRVABC59 differ by 3 amino acids, but these were not responsible for the difference in virulence between the two strains. H/PF/2013 and PRVABC59 differ by an additional 31 noncoding or silent nucleotide changes. We made a panel of chimeric viruses with identical amino acid sequences but nucleotide sequences derived from H/PF/2013 or PRVABC59. We found that 6 nucleotide differences in the 3' quarter of the H/PF/2013 genome were sufficient to confer virulence in Ifnar1 ^-/- mice. Altogether, our work identifies a large and previously unreported difference in virulence between two commonly used ZIKV strains, in two widely used mouse models of ZIKV pathogenesis (Ifnar1^-/- and Ifnar1^-/- Ifngr1^-/- DKO mice).IMPORTANCE Contemporary ZIKV strains are closely related and often used interchangeably in laboratory research. Here, we identify two strain-specific determinants of ZIKV virulence that are evident in only Ifnar1 ^-/- mice but not Ifnar1 ^-/- Ifngr1 ^-/- DKO mice. These results identify a balanced polymorphism in the E protein that is sufficient to attenuate the PRVABC59 strain but not H/PF/2013. We further identify a second virulence determinant in the H/PF/2013 strain, which is driven by the viral nucleotide sequence but not the amino acid sequence. Altogether, our work identifies a large and previously unreported difference in virulence between two commonly used ZIKV strains, in two widely used mouse models of ZIKV pathogenesis. Our results highlight that even very closely related virus strains can produce significantly different pathogenic phenotypes in common laboratory models.

SUBMITTER: Carbaugh DL

PROVIDER: S-EPMC7527068 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Ehrlichia risticii is the causative agent of Potomac horse fever (PHF), an acute infectious disease of horses. In the last few years, there have been several reports of PHF cases occurring even in vaccinated horses. We isolated a new strain of E. risticii (90-12 strain) from a vaccinated horse suffering from clinical PHF. The major pathogenic, immunologic, and molecular differences between the 90-12 strain and the 25-D stain, which was originally isolated during the outbreaks in 1984, were studied. The 90-12 strain was more pathogenic for mice and horses compared with the 25-D strain. In enzyme-linked immunosorbent assay and immunofluorescence assay with mouse and horse antisera of both the strains, two- to fourfold differences were observed between (immunoblot) with mouse and horse antisera and also with the recombinant clone-specific antibodies. Though several antigens were similar in both the strains, there were significant differences between them in the 110-, 85-, 70-, 51-, and 33-kDa antigens. The 85-kDa antigen was present only in the 90-12 strain but cross-reacted with a 50-kDa antigen of the 25-D strain. The 51-kDa antigens of both strains had different migration patterns, Southern blot hybridization of the genome from both the strains with DNA probes made from the 51-, 55-, and clones for both the strains, whereas the probe of the 85-kDa clone showed a completely different pattern. The 16S rRNA gene sequences from the two strains were identical. Neither strain replicated in gamma interferon-treated mouse peritoneal macrophages. In in vitro neutralization assay, sera from the 25-D strain-infected horse neutralized the homologous strain but did not neutralize the 90-12 strain, whereas sera from the 90-12 strain-infected horse neutralized both the strains. In mouse protection experiments, there was complete homologous protection. But in cross-protection, mice immunized with the 25-D strain were only partially protected against challenge with the 90-12 strain, whereas mice immunized with the 90-12 strain were completely protected against the 25-D strain challenge. These results clearly indicate that there are major differences between the 90-12 and 25-D strains which may have implications regarding the vaccine failure for PHF and the development of an efficient vaccine.

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Two Genetic Differences between Closely Related Zika Virus Strains Determine Pathogenic Outcome in Mice.

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