Mpox denotes a viral zoonosis caused by the Orthopoxvirus monkeypox (MPXV), which is endemic in West and Central Africa. In spring 2022, notable outbreaks of MPXV clade IIb were recorded in several high-income countries, predominantly affecting men who have sex with men (MSM). At the peak of the outbreak, over 200 new mpox cases per week were reported in Berlin, which constitutes one of the largest MSM population in Europe. Within the same year, the outbreak significantly declined, and it is unclear which factors contributed to this rapid decrease. To investigate the concomitant effects of sexual contact networks, transient contact reductions and the effect of infection- vs. vaccine-derived immunity on the 2022 mpox outbreak, we calibrated an agent-based model with epidemic, vaccination, contact- and behavioral data. Our results indicate that vaccination has a marginal effect on the epidemic decline. Rather, a combination of infection-induced immunity of high-contact individuals, as well as transient behavior changes reduce the number of susceptible individuals below the epidemic threshold. However, the 2022 mpox vaccination campaign, together with infection-derived immunity may contribute to herd-immunity in the Berlin MSM population against ongoing clade I mpox outbreaks. Demographic changes and immune waning may deteriorate this herd immunity over time. These findings highlight that, in addition to vaccination, timely and clear communication of transmission routes may trigger spontaneous protective behavior within key populations; underscoring the importance of targeted sexual health education as a core component of outbreak response. Mpox is a virus disease that is transmitted through direct contact with infected individuals or contaminated materials. In 2022, major Mpox outbreaks occurred in several countries, especially among men who have sex with men (MSM). At its peak, Berlin (Germany) reported over 200 new cases per week, but saw a rapid decline of cases during summer 2022. We used mathematical simulations to explore how patterns of sexual contact, temporary changes in behavior, and immunity from infection or vaccination may have impacted the outbreak. We found that vaccination had a minor effect, while immunity from past infections and behavior changes played a major role in reducing infections. These insights show that clear communication about virus spread can encourage protective behaviors, highlighting the importance of targeted sexual health education in containing sexually transmitted infections. Gubela et al. calibrate an adaptive agent-based model with intra-host dynamics to investigate the 2022 Mpox outbreak dynamics in Berlin. Behavioral change and infection-induced immunity are the main reasons for outbreak decline, while the effect of vaccination is marginal.

Staphylococcal enterotoxins (SEs) are major contributors to foodborne intoxications. Reliable detection methods for SEs are essential to maintain food safety and protect public health. Since the heat-stable toxins also exert their toxic effect in the absence of the bacterium, reliance on DNA detection alone can be misleading: it does not allow for determining which specific toxins encoded by a given strain are produced and epidemiologically linked with a given outbreak. Commercially available diagnostic assays for SE detection are so far limited in sensitivity and specificity as well as in the range of targeted toxins (SEA-SEE), thus non-targeted SEs linked to foodborne illness remain undetected at the protein level. This study aimed to develop a highly sensitive and specific multiplex suspension immunoassay (SIA) for SEA to SEI. To this end, high-affinity monoclonal antibodies (mAbs) for the specific detection of the individual SEs were generated. When implemented in sandwich ELISAs and multiplex SIA, these mAbs demonstrated exceptional sensitivity with detection limits in the low picogram per millilitre range. When applied for the analysis of SE production in liquid cultures of a panel of 145 whole-genome sequenced strains of Staphylococcus spp. and Enterococcus faecalis, the novel multiplex SIA detected and differentiated the eight SEs with assay accuracies of 86.9-100%. Notably, the multiplex SIA covered one to four sequence variants for each of the individual SEs. Validation confirmed high recovery rates and reliable performance in three representative complex food matrices. The implementation of the novel mAbs in a multiplex SIA enabled, for the first time, simultaneous detection, differentiation, and quantification of multiple SEs from minimal sample volumes using Luminex® technology. As a result, the multiplex SIA will help strengthen food safety protocols and public health response capabilities.

Ricin, a ribosome-inactivating lectin from Ricinus communis seeds, has been used as a bioterrorism agent in multiple cases. While passive immunotherapy with anti-ricin antibodies shows promise in preclinical studies, no approved countermeasure exists. Developing effective monoclonal antibodies (mAbs) is challenging, requiring epitope targeting that ensures neutralization of the two most dominant natural ricin isoforms (D and E). Moreover, high-affinity binding does not always correlate with toxin neutralization, highlighting the importance of epitope specificity in driving protection. Here, we characterized a panel of 17 anti-ricin antibodies, including VHH and IgG mAbs, to determine their affinities, selectivity, and epitopes. Using surface plasmon resonance (SPR) and biolayer interferometry (BLI), we evaluated antibody affinities for the two ricin isoforms (D and E), as well as for ricin agglutinin, a related lectin with markedly lower toxicity. Epitope determination was performed using (1) SPR-based epitope binning, enhanced by network analysis for streamlined bin visualization, and (2) deep mutational scanning with yeast surface display to identify key epitope residues. BLI effectively distinguished low- and high-affinity interactions, while SPR provided superior resolution for determining the highest affinities and lowest dissociation rates. Both epitope-mapping strategies yielded highly consistent results, allowing the identification of critical epitopes associated with potent neutralization and cross-reactivity between ricin isoforms. This study advances our understanding of ricin neutralization by this panel of antibodies, providing key insights into their affinity, epitope specificity, and cross-reactivity. These findings contribute to the rational design of antibody-based therapeutics for ricin intoxication.

The 2022 global mpox outbreak highlighted the risk of zoonotic diseases establishing sustained transmission in human populations and underscored the need for accurate serological tools to monitor orthopoxvirus exposure. However, cross-reactive antibodies induced by Modified Vaccinia Ankara (MVA) vaccination make it difficult to discriminate between monkeypox virus (MPXV) infection and vaccination-induced immunity. Here we present a machine learning (ML)-assisted bead-based serological multiplex assay that distinguishes MPXV infection from MVA vaccination and pre-immune sera by targeting antibody responses to 15 poxviral antigens. Of the six algorithms tested, the Gradient Boosting Classifier (GBC) achieves the highest performance (F1 = 0.83) in sera from the 2022 outbreak and from a follow-up epidemiological cohort of at-risk men who have sex with men (MSM; n = 1,260). In an independent validation cohort (n = 143), GBC (F1 = 0.70) robustly detects MPXV infections, including breakthrough cases, with 88% specificity and 92% sensitivity. Integrating ML with high-dimensional serology enables accurate cross-sectional classification of orthopoxvirus immune status and provides a scalable framework for mpox serosurveillance and outbreak preparedness.

Staphylococcal enterotoxins (SEs) belong to a family of highly potent superantigens produced by Staphylococcus aureus and play a significant role in food poisoning and toxic shock syndrome. Among the SE family type B (SEB) is unique as it is involved in naturally occurring diseases and also has a history of military use as an incapacitating agent. Thus, the accurate detection of SEs and particularly SEB is critical. However, immuno-based detection methods encounter intrinsic difficulties due to S. aureus' co-production of staphylococcal protein A (SpA), which has a strong affinity for immunoglobulins. This interaction can result in false-positive results in antibody-based assays, thereby complicating the interpretation of results with regard to presence and quantity of SEB. Commercially available detection methods seek to address this issue through SpA depletion by pre-incubating samples with animal serum. While these approaches mitigate the impact of SpA interference, they frequently result in diminished assay sensitivity. In this study, a previously established highly sensitive sandwich enzyme-linked immunosorbent assay (ELISA) for SEB detection was optimised to maintain its low detection limit in the one-digit pg/mL-range while simultaneously abolishing its reactivity to SpA in S. aureus liquid-culture supernatants. The modifications were focused on direct alterations to existing detection antibodies by a) adapting the immunoglobulin subclass and generation of antibody fragments through recombinant technology, and b) the careful selection of control capture antibodies. This study can be taken as a blueprint for optimised ELISA strategies to overcome SpA related false results while maintaining high sensitivity for SE detection and quantification.

Botulism is a potentially life-threatening disease caused by botulinum neurotoxin (BoNT)-producing bacteria of the genus Clostridium. Laboratory detection of BoNTs in patients’ samples is essential to confirm clinical diagnoses and to identify the causative BoNT serotype. The current ’gold standard’ method for BoNT detection is the mouse bioassay (MBA), a highly stressful animal experiment. A viable animal experiment replacement method must demonstrate high sensitivity, specificity, reproducibility and robustness, as well as comprehensive BoNT subtype detection, and be widely accepted in the field, necessitating rigorous validation. Here, we report on the validation of a previously established in vitro endopeptidase suspension immunoassay (Endopep-SIA) for the simultaneous detection, differentiation and quantification of BoNT serotypes A and B, the most frequent serotypes associated with human botulism. This assay uses monoclonal antibodies for BoNT extraction, followed by detection of the catalytic activity using neoepitope-specific monoclonal antibodies and suspension array technology. The Endopep-SIA showed high reproducibility with intra- and inter-assay variabilities between 7 and 22%, it demonstrated a sensitivity two- to twenty-fold higher than the MBA for BoNT in buffer samples and was equally sensitive for human serum samples with a limit of detection of 0.4 MLD/mL for BoNT/A and 1.0 MLD/mL for BoNT/B. Importantly, it reliably detected all six BoNT/A and six BoNT/B subtypes tested, including clinically relevant and bivalent strains, hereby proving high diagnostic safety. Based on the results obtained, we expect the Endopep-SIA to be instrumental in markedly reducing the number of animals used in botulism diagnostics.

Because of their superior properties for certain biological applications small antibody derivatives like fragment of antigen binding (Fab) have found widespread use in basic research and as therapeutics. However, generation of Fab-fragments is still a rather complex matter, reflected by the fact that a variety of methods and purification techniques are necessary for the production of all the different classes of Fab-fragments (kappa/lambda light chains, type of species). Here we demonstrate that Fab-fragments derived from six different antibodies of human or murine origin produced by transient expression in HEK cells can be purified in a single step to a high degree of purity by standard protein G affinity chromatography. This is most likely due to alternative contact sites for protein G located in the CH1 domain of the Fab heavy chain. Our data demonstrate that protein G affinity chromatography as for whole antibodies is a robust method for the purification of tag-less Fab-fragments independent of species, significantly simplifying the process of Fab-fragment purification.

Abstract Introduction During the mpox outbreak in 2022, the highest number of cases in Germany were registered in Berlin, almost all of them in men who have sex with men (MSM). However, the frequency of clinically undiagnosed infections is unknown. Methods A cross-sectional study was conducted among MSM in Berlin, Germany. Participants were recruited from private practices and community-based checkpoints specialised in HIV and STI care for MSM. They were asked to complete an online questionnaire on socio-demographic data, mpox diagnosis, vaccination history and sexual behaviour, and to provide a blood sample for serological analysis. The samples were tested for antibodies against a range of antigens to distinguish between antibodies induced by mpox infection and MVA vaccination, with pre-immune sera from childhood smallpox vaccination as a confounding factor. Associations of behavioural variables with reported and suspected mpox diagnosis as the outcome were tested using univariable and multivariable logistic regression models. Results Between the 11th April and 1st July 2023, 1,119 participants were recruited in eight private practices and two community-based checkpoints in Berlin. All participants provided a blood sample for serological testing. Information for the online questionnaire was provided by 728 participants; core data on age and mpox history for participants who did not provide questionnaire data were provided by the practices for an additional 218 participants. A previous diagnosis of mpox was reported for/by 70 participants (7.4%). Using a conservative and strict case definition, we serologically identified an additional 91 individuals with suspected undiagnosed mpox infection. Individuals with reported or suspected mpox infections reported more condomless anal sex partners in the past 3 months (OR = 5.93; 95% CI 2.10-18.35 for 5–10 partners; OR = 9.53; 95% CI 2.72–37.54 for > 10 partners) and were more likely to report sexual contact with partners diagnosed with mpox (OR = 2.87; 95% CI 1.39–5.84). Conclusion A substantial proportion of mpox infections were clinically undiagnosed. The number of condomless anal sex partners was strongly associated with both confirmed and suspected undiagnosed mpox infection. Therefore, mpox control measures based on clinical diagnosis of mpox are likely to have limited effectiveness in preventing mpox transmission in outbreak situations because many infections remain unrecognised and undiagnosed.

Measles is a highly contagious airborne viral disease. It can lead to serious complications and death and is preventable by vaccination. The live-attenuated measles vaccine (LAMV) derived from a measles virus (MV) isolated in 1954 has been in use globally for six decades and protects effectively by providing a durable humoral and cell-mediated immunity. Our study addresses the temporal stability of epitopes on the viral surface glycoprotein hemagglutinin (H) which is the major target of MV-neutralizing antibodies. We investigated the binding of seven vaccine-induced MV-H-specific monoclonal antibodies (mAbs) to cell-free synthesized MV-H proteins derived from the H gene sequences obtained from a lung specimen of a fatal case of measles pneumonia in 1912 and an isolate from a current case. The binding of four out of seven mAbs to the H protein of both MV strains provides evidence of epitopes that are stable for more than 100 years. The binding of the universally neutralizing mAbs RKI-MV-12b and RKI-MV-34c to the H protein of the 1912 MV suggests the long-term stability of highly conserved epitopes on the MV surface.

With case numbers exceeding 97,000 worldwide, the 2022 global mpox outbreak underscored the potential for zoonotic diseases with limited human-to-human transmission to trigger a widespread health crisis. Primarily men who have sex with men (MSM) were affected. Monitoring mpox-specific seroprevalences through epidemiological studies is essential, but challenging due to the cross-reactive antibody immune response which is induced by several orthopoxviruses including modified vaccinia virus Ankara (MVA)-based vaccines, which were used to help bring the outbreak under control. Here we show how machine learning (ML)-guided analysis of a serological multiplex assay that targets 15 immunogenic poxvirus proteins derived from monkeypox virus, vaccinia, and cowpox virus, can confidently discern between sera from patients post-mpox infection, post-MVA immunization, and pre-immunization or infection. Mean F1 scores representing the geometric means between precision and recall were calculated as metrics for the performance of six different ML models. The models were trained and tested on panels containing both sera taken in the early phase of seroconversion as well as sera taken six months after the peak of the mpox outbreak from individuals in an at-risk MSM population in Berlin. Scores ranged between 0.60 ± 0.05 and 0.81 ± 0.02 with Gradient Boosting Classifier (GBC) being the best performing algorithm. In order to ensure high confidence in our results, which is imperative in epidemiological studies, we excluded ambiguous results by using the robustly performing linear discriminant analysis’ (mean F1 scores 0.80 ± 0.02) classification confidence as a threshold. Hereby, sera with uncertain serostatus were segregated, leading to confident predictions with F1 scores above 0.90, at the cost of more inconclusive results for samples below the threshold. Beyond providing a valuable tool for monitoring mpox-specific antibodies, our work demonstrates how the combination of machine learning and multiplexing enables precise differentiation — and a deepened understanding — of complex antibody responses to closely related viruses.

In the recent mpox outbreak, people with human immunodeficiency virus (PWH) were at high risk both for contracting infection and for a more severe disease course. We studied cellular and humoral immune responses elicited by mpox infection (n = 5; n = 3 PWH) or smallpox vaccination (n = 17; all PWH) in a cohort of men who have sex with men. All PWH were successfully treated, with stable CD4 counts and undetectable HIV viral loads. Eleven of 17 vaccinated individuals had received childhood smallpox vaccination. In this group of individuals, both 2-dose modified vaccinia Ankara (MVA) vaccination and natural infection evoked mpox-specific immune responses mediated by B cells as well as CD4 and CD8 T cells. This study improves our understanding of smallpox vaccination-mediated cross-reactivity to other orthopox viruses, and long-lasting durability of childhood smallpox vaccination-mediated immune responses, including in PWH.

We included 852 patients in a prospectively recruiting multicenter matched case-control study in Germany to assess vaccine effectiveness (VE) in preventing COVID-19-associated hospitalization during the Delta-variant dominance. The two-dose VE was 89 % (95 % CI 84-93 %) overall, 79 % in patients with more than two comorbidities and 77 % in adults aged 60-75 years. A third dose increased the VE to more than 93 % in all patient-subgroups. (c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).

Serological assays measuring antibodies against SARS-CoV-2 are key to describe the epidemiology, pathobiology or induction of immunity after infection or vaccination. Of those, multiplex assays targeting multiple antigens are especially helpful as closely related coronaviruses or other antigens can be analysed simultaneously from small sample volumes, hereby shedding light on patterns in the immune response that would otherwise remain undetected. We established a bead-based 17-plex assay detecting antibodies targeting antigens from all coronaviruses pathogenic for humans: SARS-CoV-2, SARS-CoV, MERS-CoV, HCoV strains 229E, OC43, HKU1, and NL63. The assay was validated against five commercial serological immunoassays, a commercial surrogate virus neutralisation test, and a virus neutralisation assay, all targeting SARS-CoV-2. It was found to be highly versatile as shown by antibody detection from both serum and dried blot spots and as shown in three case studies. First, we followed seroconversion for all four endemic HCoV strains and SARS-CoV-2 in an outbreak study in day-care centres for children. Second, we were able to link a more severe clinical course to a stronger IgG response with this 17-plex-assay, which was IgG1 and IgG3 dominated. Finally, our assay was able to discriminate recent from previous SARS-CoV-2 infections by calculating the IgG/IgM ratio on the N antigen targeting antibodies. In conclusion, due to the comprehensive method comparison, thorough validation, and the proven versatility, our multiplex assay is a valuable tool for studies on coronavirus serology.

Purpose COViK, a prospective hospital-based multicenter case-control study in Germany, aims to assess the effectiveness of COVID-19 vaccines against severe disease. Here, we report vaccine effectiveness (VE) against COVID-19-caused hospitalization and intensive care treatment during the Omicron wave. Methods We analyzed data from 276 cases with COVID-19 and 494 control patients recruited in 13 hospitals from 1 December 2021 to 5 September 2022. We calculated crude and confounder-adjusted VE estimates. Results 21% of cases (57/276) were not vaccinated, compared to 5% of controls (26/494; p < 0.001). Confounder-adjusted VE against COVID-19-caused hospitalization was 55.4% (95% CI: 12–78%), 81.5% (95% CI: 68–90%) and 95.6% (95%CI: 88–99%) after two, three and four vaccine doses, respectively. VE against hospitalization due to COVID-19 remained stable up to one year after three vaccine doses. Conclusion Three vaccine doses remained highly effective in preventing severe disease and this protection was sustained; a fourth dose further increased protection.

The monkeypox virus (MPXV) outbreak in 2022 has renewed interest in the detection of antibodies against orthopox viruses (OPXV) and MPXV, as serological methods can aid diagnostics and are key to epidemiological studies. Here three complementary serological methods are described with different strengths to aid the development and evaluation of in-house assays: An immunofluorescence assay (IFA) for specific detection of IgG and IgM, an enzyme-linked immunosorbent assay for higher sample throughput to aid epidemiological studies and a neutralization test to detect virus neutralizing antibodies. As implementation of MPXV-specific diagnostics is often hampered by the requirement for a dedicated biosafety level 3 laboratory (BSL-3), the focus of this study is on biosafety aspects to facilitate safe testing also under BSL-2 conditions. To this aim, it was analyzed whether OPXV, which can be handled under BSL-2 conditions, could be used as less virulent alternatives to MPXV. Furthermore, an inactivation method was established to remove up to five log-steps of infectious virus particles from viraemic sera without compromising antibody detection. The results show that immunological cross-reactivity between OPXV provides an opportunity for the interchangeable usage of different OPXV species in serological assays, enabling MPXV serology outside of BSL-3 facilities.

Gram-positive bacteria are protected by a thick mesh of peptidoglycan (PG) completely engulfing their cells. This PG network is the main component of the bacterial cell wall, it provides rigidity and acts as foundation for the attachment of other surface molecules. Biosynthesis of PG consumes a high amount of cellular resources and therefore requires careful adjustments to environmental conditions. An important switch in the control of PG biosynthesis of Listeria monocytogenes, a Gram-positive pathogen with a high infection fatality rate, is the serine/threonine protein kinase PrkA. A key substrate of this kinase is the small cytosolic protein ReoM. We have shown previously that ReoM phosphorylation regulates PG formation through control of MurA stability. MurA catalyzes the first step in PG biosynthesis and the current model suggests that phosphorylated ReoM prevents MurA degradation by the ClpCP protease. In contrast, conditions leading to ReoM dephosphorylation stimulate MurA degradation. How ReoM controls degradation of MurA and potential other substrates is not understood. Also, the individual contribution of the ~20 other known PrkA targets to PG biosynthesis regulation is unknown. We here present murA mutants which escape proteolytic degradation. The release of MurA from ClpCP-dependent proteolysis was able to activate PG biosynthesis and further enhanced the intrinsic cephalosporin resistance of L. monocytogenes. This latter effect required the RodA3/PBP B3 transglycosylase/transpeptidase pair. One murA escape mutation not only fully rescued an otherwise non-viable prkA mutant during growth in batch culture and inside macrophages but also overcompensated cephalosporin hypersensitivity. Our data collectively indicate that the main purpose of PrkA-mediated signaling in L. monocytogenes is control of MurA stability during standard laboratory growth conditions and intracellular growth in macrophages. These findings have important implications for the understanding of PG biosynthesis regulation and β-lactam resistance of L. monocytogenes and related Gram-positive bacteria.