In-field detection and characterization of B/Victoria lineage deletion variant viruses causing early influenza activity and an outbreak in Louisiana, 2019

Background

In 2019, the Louisiana Department of Health reported an early influenza B/Victoria (B/VIC) virus outbreak.

Method

As it was an atypically large outbreak, we deployed to Louisiana to investigate it using genomics and a triplex real-time RT-PCR assay to detect three antigenically distinct B/VIC lineage variant viruses.

Results

The investigation indicated that B/VIC V1A.3 subclade, containing a three amino acid deletion in the hemagglutinin and known to be antigenically distinct to the B/Colorado/06/2017 vaccine virus, was the most prevalent circulating virus within the specimens evaluated (86/88 in real-time RT-PCR).

Conclusion

This work underscores the value of portable platforms for rapid, onsite pathogen characterization.

Development and evaluation of a conventional RT-PCR for differentiating emerging influenza B/Victoria lineage viruses with hemagglutinin amino acid deletion from B/Yamagata lineage viruses

BACKGROUND

Recent influenza B/Victoria lineage viruses contain amino acid deletions at positions 162 to 164 of the haemagglutinin (HA) protein. These amino acid deletions have affected the detection of B/Victoria lineage viruses by the lineage-specific conventional reverse-transcription polymerase chain reaction (RT-PCR) that was recommended by World Health Organization (WHO).

OBJECTIVES

We aimed to develop and evaluate a novel lineage-specific RT-PCR for rapid differentiation of the contemporary B/Victoria lineage from B/Yamagata lineage viruses.

STUDY DESIGN

Primers of our in-house RT-PCR were designed to avoid amino acid positions 162 to 164 and to target conserved regions of the HA gene that are specific for B/Victoria and B/Yamagata lineage viruses. Our in-house RT-PCR and WHO RT-PCR were evaluated using influenza B positive clinical specimens or virus culture isolates. Influenza B virus lineage was confirmed by Sanger sequencing.

RESULTS

A total of 105 clinical specimens or virus culture isolates were retrieved, including 83 with B/Victoria lineage and 22 with B/Yamagata lineage viruses. Our in-house RT-PCR correctly identified B/Victoria lineage viruses in all 83 samples, including 82 samples with double or triple amino acid deletion in the HA protein. Conversely, the WHO lineage-specific conventional RT-PCR failed to detect any of the 82 samples with HA amino acid deletions. For the 22 samples with B/Yamagata lineage viruses, both RT-PCR assays have correctly identified B/Yamagata lineage in all samples.

CONCLUSIONS

Our novel lineage-specific RT-PCR has successfully detected all contemporary B/Victoria lineage viruses with amino acid deletions in HA. This protocol is especially useful for laboratories without the equipment for real-time PCR.

A stretch of residues within the protease-resistant core is not necessary for prion structure and infectivity

Mapping out regions of PrP influencing prion conversion remains a challenging issue complicated by the lack of prion structure. The portion of PrP associated with infectivity contains the α-helical domain of the correctly folded protein and turns into a β-sheet-rich insoluble core in prions. Deletions performed so far inside this segment essentially prevented the conversion. Recently we found that deletion of the last C-terminal residues of the helix H2 was fully compatible with prion conversion in the RK13-ovPrP cell culture model, using 3 different infecting strains. This was in agreement with preservation of the overall PrP^C structure even after removal of up to one-third of this helix. Prions with internal deletion were infectious for cells and mice expressing the wild-type PrP and they retained prion strain-specific characteristics. We thus identified a piece of the prion domain that is neither necessary for the conformational transition of PrP^C nor for the formation of a stable prion structure.