Correlation between monkeypox viral load and infectious virus in clinical specimens

BACKGROUND

In the 2022 mpox outbreak, several studies have explored longitudinal DNA shedding of mpox virus (MPXV) using PCR. However, there are fewer studies assessing infectivity in cell culture, and, by inference, MPXV transmissibility. Such information could help inform infection control and public health guidelines.

AIMS AND METHODS

The aim of this study was to correlate cell culture infectivity of clinical samples with viral loads in clinical samples. Between May to October 2022, clinical samples from different body sites sent to the Victorian Infectious Diseases Reference Laboratory in Melbourne, Australia for MPXV PCR detection were cultured in Vero cells as a surrogate for infectivity.

RESULTS

In the study period, 144 samples from 70 patients were tested by MPXV PCR. Viral loads in skin lesions were significantly higher than those in throat or nasopharyngeal samples (median Ct 22.0 vs 29.0, p = 0.0013 and median Ct 22.0 vs 36.5, p = 0.0001, respectively). Similarly, viral loads were significantly higher in anal samples compared to throat or nasopharyngeal samples (median Ct 20.0 vs. 29.0, p=<0.0001 and median Ct 20.0 vs. 36.5, p=<0.0001, respectively). Viral culture was successfully performed in 80/94 samples. Using logistic regression analysis, 50% of the samples were positive in viral culture at Ct 34.1 (95% confidence intervals 32.1-37.4).

CONCLUSIONS

Our data further validate recent findings showing that samples with a higher MPXV viral load are more likely to demonstrate infectivity in cell culture. Although the presence of infectious virus in cell culture may not directly translate with clinical transmission risk, our data may be used as an adjunct help inform guidelines on testing and isolation policies in individuals with mpox.

Predicting HBsAg clearance in genotype A chronic hepatitis B using HBsAg epitope profiling: A biomarker for functional cure

BACKGROUND AND AIM

Functional cure is the major goal of chronic hepatitis B (CHB) therapy though few biomarkers predict this outcome. HBsAg epitope occupancy can be influenced by therapeutic and immune pressure. The aim of this study was to map the HBsAg epitope profiles during long-term nucleos(t)ide analogue therapy in patients with genotype A CHB, in the context of HBsAg loss (SL)/seroconversion.

METHODS

We evaluated 25 genotype A CHB patients in the GS-US-174-0103 trial of HBeAg-positive CHB patients treated with tenofovir or adefovir for 4 years, 14 who achieved SL whilst 11 had no change. We epitope mapped the major domains of HBsAg to identify those patients with HBsAg clearance profile (CP) (loss of binding at both loops 1 and 2 epitopes of the 'a' determinant) vs non-clearance profile (no change in epitope recognition, or loss of epitope binding at one loop only), correlating this to on-treatment HBsAg responses. Complexed anti-HBs was also measured.

RESULTS

Analysis of the HBsAg epitope profiles of the 25 patients at baseline identified no predictive correlation with SL. In contrast, analysis at week 48 and end of study (week 192) or prior to SL identified significant predictive associations between development of HBsAg CPs and outcome of functional cure. The detection of a CP also correlated with the development of an alanine aminotransferase flare and detection of anti-HBs complexed with HBsAg.

CONCLUSION

The detection of HBsAg CPs by epitope mapping represents a novel viral biomarker, reflecting an emerging anti-HBs selection pressure prior to functional cure.