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Develop Highly Sensitive Mpox (Monkeypox) Assays Using Specimen-specific TM Master Mixes
nucleases 3 . These inhibitory components can impede a molecular assay if they are not removed or inactivated before testing. Meridian’s Lyo-Ready Direct DNA LAMP Saliva (MDX134) and Air-Dryable™ Direct DNA qPCR Saliva (MDX130) mixes are optimized to work on liquid samples containing a range of inhibitors, including VTM. An in-house study using primers and probes specifically designed for MPXV detection was conducted to demonstrate the mixes’ ability to amplify MPXV DNA in the presence of 10% VTM and 20% VTM. In addition, the sensitivity and reproducibility of the saliva mixes were compared against mixes from NEB and Themo to demonstrate their superior performance for MPXV detection. Specifically, two sets of primers were designed, one set to detect the mpox A-type inclusion (ATI) gene region (a unique 453-nucleotide residue in the West African strains but not in the Congo Basin strains) and a second set to detect the G2RG region within the tumor necrosis factor receptor gene (which is capable of detecting all known strains of MPXV). In the first study, the amplification sensitivity of Lyo-Ready Direct DNA LAMP Saliva was compared against NEB WarmStart ® and Thermo SuperScript™ IV in a titration assay spiked with 6,000, 600 or 60 copies of MPX DNA in the presence of 10% VTM or 20% VTM. Lyo-Ready Direct DNA LAMP Saliva exhibited the earliest time-to-results (TTR) across all samples, indicating greater sensitivity and reproducibility, particularly with low copies of the viral DNA. The second study examined the reproducibility of Air-Dryable™ Direct DNA qPCR Saliva against Thermo TaqPath™ ProAmp Multiplex Master Mix in a serial dilution assay using 2,000, 200 or 20
reactivity between orthopoxviruses which limits the use of serology assays in providing monkeypox-specific confirmation. The best diagnostic specimens are obtained directly from the rash- such as skin samples, fluid, or crusts. If skin lesions are not present, testing can be performed using oropharyngeal, anal, or rectal swabs. Mpox Molecular Assays Molecular testing for mpox has expanded in recent years, with 89 different assays recognized by the FDA 1 . In updated 2024 guidelines released by the WHO, clade- specific PCR assays should be used in conjunction with an OPXV generic or mpox generic PCR test that targets conserved genes, especially when confirming an outbreak or a new case in a previously non-outbreak area 2 . It is important for assays to target conserved orthopoxvirus (OPXV) or MPXV genes, to minimize the risk of assays being affected by sequence variants or gene dropouts. This strategy ensures detection of the novel mpox strains circulating in a region. The ideal specimen type for mpox is skin lesion material placed in viral transport media (VTM). Oropharyngeal swabs may also be used, however data on the accuracy of this specimen type for diagnosis is limited for mpox. DNA extracted from whole blood is not considered a suitable specimen as the viraemic phase on the infection may have already passed at the time of rash onset. Selecting the best reagents that perform accurately with lesion swabs and VTM is a critical step in developing a highly sensitive and specific mpox assay. Although VTM is designed to maintain the stability of viruses, some VTMs which are formulated to inactivate viruses and bacteria contain components that inhibit the activity of
Introduction Mpox (monkeypox, MPXV) virus is a zoonotic double-stranded DNA enveloped virus that belongs to the Orthopoxvirus genus of the Poxviridae family which also includes variola (VARV), cowpox (CPX), and vaccinia (VACV) viruses. The mpox virus is endemic to Africa with two distinct genetic groups (clades): clade I (once known as the Congo Basin clade), which historically has a higher death rate, and clade II (formerly the West African clade). In August 2024, the WHO declared a global health emergency in response to the outbreak of mpox that originated in the Democratic Republic of Congo (DRC) and has since spread to a growing number of countries in Africa. More than 15,600 mpox cases and 537 deaths have been detected in the DRC this year, with children being significantly affected. The current outbreak is being driven by a new offshoot of clade 1, known as clade 1b, which appears to spread easily through close contact. For the first time, clade 1 mpox is also spreading via sexual contact. Mpox has an incubation period of 4 to 21 days and the symptoms range from fever to respiratory distress with a characteristic rash and pustules/lesions developing a few days after the first symptoms. The virus is spread through contact with damaged skin, the respiratory tract or the mucous membrane (eyes, nose or mouth). Within the general population, the fatality rate of mpox can be up to 11% and is higher among young children, the elderly, pregnant women and immunocompromised individuals. The WHO currently recommends diagnostic testing using nucleic acid amplification (NAAT) techniques such as qPCR or LAMP- this is due to cross-
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Study 1: Speed and Reproducibility of Lyo-Ready Direct DNA LAMP Saliva (MDX134) with the ATI Gene and Viral Transport Media (VTM)
copies of MPXV DNA (over 6 repeats for each dilution). The results illustrate the greater reproducibility of the Air-Dryable™ Saliva mix, leading to increased sensitivity and specificity of MPXV detection, particularly when only low copies of the viral DNA are present.
A)
A) Lyo-Ready Direct DNA LAMP Saliva (MDX134) was lyophilized with ATI primers and used for the amplification of a 10-fold serial dilution of MPXV DNA (6,000, 600 and 60 copies respectively) in the presence of 10% VTM and 20% VTM. The time to results (TTR) values were compared to the same primers and DNA with NEB WarmStart ® and Thermo SuperScript™ IV.
B)
10% VTM- 60 copies
20% VTM- 600 copies
Lyophilized MDX134 | NEB WarmStart ® | Thermo SuperScript™ IV RT-LAMP
B) In order to illustrate the results further, the results of Lyo-Ready Direct DNA LAMP Saliva (MDX134) ( red ), NEB WarmStart ® ( orange ) and Thermo SuperScript™ IV ( black ) for the 60 copies of MPXV DNA in 10% VTM and 600 copies of MPXV DNA in 20% VTM are also displayed as amplification plots. The results illustrate the increased speed and specificity of the Lyo-Ready Direct DNA LAMP Saliva, with earlier TTR and greater reproducibility, particularly with low copies of the viral DNA.
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Study 2: Sensitivity and Reproducibility of Air-Dryable™ Direct DNA qPCR Saliva (MDX130) with the ATI and G2R-G Gene
ATI gene
G2R-G
Human RNaseP
2000 copies 200 copies
2000 copies 200 copies
2000 copies 200 copies
20 copies
20 copies
20 copies
Air-Dryable™ Direct DNA qPCR Saliva (MDX130) ( red ) was dried with ATI primers, G2R-G or human RNaseP (as an internal control) and used for the amplification of a 10-fold serial dilution of MPXV DNA (2,000, 200 and 20 copies respectively), using 6 repeats of each dilution. The results were compared to the same primers and DNA for Thermo TaqPath™ ProAmp Multiplex Master Mix ( black ). The results illustrate the increased sensitivity and specificity of the Air-Dryable™ Direct DNA qPCR Saliva, with better sensitivity, specificity and reproducibility, particularly with low copies of the viral DNA.
Conclusion As the mpox outbreak continues to grow, the need for highly sensitive and specific detection assays increases. We have shown that both our qPCR and LAMP Sample- specific™ Saliva mixes can be used to develop fast, sensitive and reproducible assays for the detection of mpox using specimens containing VTM. These mixes are fully optimized and only require the addition of primers and probes as demonstrated in our studies. Ready-to-use mixes such as ours, enable assay manufacturers to fast-track their assay development for mpox, avoiding the need for extensive optimization of reagents compatible with inhibitors present in VTM solutions. In addition, the mixes are both formulated to be dried down, either by lyophilization (Lyo-Ready) or air-dried (Air-Drayble™), simplifying the process of creating ambient- temperature stable assays. Assays that can be shipped and stored at room-temperature should be particularly beneficial in remote regions such as Africa, where testing facilities and other resources are limited but the virus is endemic. Although the future recommendations for mpox testing remain unknown, as more recommendations will evolve. Very recent research suggests that mpox infections can be asymptomatic, which indicates the potential need for wider testing and information is uncovered on mpox transmission, it is likely that testing
isolation policies among people exposed to the virus 4 . If screening expands to individuals exposed to active mpox cases, then testing may need to include molecular screening using blood specimens and serology-based immunoassays that can detect acute subclinical and asymptomatic infections. In previous mpox outbreaks, such as the one in 2003 in the United States, serologic assays provided significant diagnostic support. Mpox IgM capture assays were able to distinguish between vaccinated and unvaccinated individuals with a sensitivity and specificity of 95% 5 . Overall, a coordinated, worldwide effort will be required to stop the mpox outbreak, and a significant scale-up in testing will be most likely be required in regions around the globe, especially where case numbers are the highest.
1. FDA “Monkeypox (mpox) and Medical Devices”. Retrieved from: https://www.fda.gov/ medical-devices/emergency-situations-medical- devices/monkeypox-mpox-and-medical-devices 2. World Health Organization. Diagnostic Testing for the Monkeypox Virus (MPXV): Interim Guidance. 10 May 2024. Retrieved from: https:// iris.who.int/bitstream/handle/10665/376952/ WHO-MPX-Laboratory-2024.1-eng. pdf?sequence=1 3. Daum L.T., et al. A clinical specimen collection and transport medium for molecular diagnostic and genomic applications. Epidemiol. Infect. 2011; 139: 1764e73. https://doi.org/10.1017/ S0950268810002384 4. Baetselier, I.D, et al . Asymptomatic mpox virus infections among male sexual health clinic attendees in Belgium. medRxiv 2022.07.04.22277226. https://doi. org/10.1101/2022.07.04.22277226 5. Karem, K.L., et al . Characterization of Acute-Phase Humoral Immunity to Mpox: Use of Immunoglobulin M Enzyme-Linked Immunosorbent Assay for Detection of Mpox Infection during the 2003 North American Outbreak. Clinical and Vaccine Immunology. 2005; 12: 7. https://doi.org/10.1128/ CDLI.12.7.867-872.2005
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