Matthew Benjamin Bransby McCall

This cross-sectional study investigates the spectrum and proportion of multidrug-resistant (MDR) bacteria isolated from clinical samples processed at the regional microbiology laboratory of Lambaréné, Gabon. Bacteriological results from 2017 to 2023 were retrospectively analysed to assess the rates of non-susceptibility among the most common isolates from urine, blood, stool, and swabs (wound, urethral, ear, and throat). Antimicrobial susceptibility testing and interpretation were performed according to Clinical Laboratory Standards Institute (CLSI) guidelines.A total of 5,401 cultures were reviewed, with 1,050 yielding clinically relevant bacterial isolates. The most frequently identified pathogens were Escherichia coli (273/1050; 26%), Staphylococcus aureus (192/1050; 18%), β-hemolytic Streptococci (160/1050; 15%), and Klebsiella pneumoniae (69/1050; 6.6%). Urine samples predominantly yielded E. coli and K. pneumoniae , while S. aureus was most common in wound and blood cultures. Overall, 23% (242/1050) of isolates were classified as MDR, with E. coli accounting for 40% (96/1050). The proportion of ESBL producers among Enterobacterales was 10% (55/522). Resistance to third-generation cephalosporins was notably high, especially among K. pneumoniae (28/69; 41%) and E. coli (34/273; 13%). Methicillin-resistant S. aureus (MRSA) represented 12% (22/192) of S. aureus isolates; 5.5% (58/1050) of isolates belong to the WHO critical-priority pathogen group.Clinical microbiology data from Lambaréné indicate that urinary infections are mainly associated with E. coli , whereas S. aureus predominates in wound swabs and blood cultures. The detection of WHO critical-priority pathogens in this setting supports the need for sustained microbiological monitoring and locally adapted measures to improve antibiotic use and infection prevention.

Andes virus (ANDV) is unique among hantaviruses because person-to-person transmission ispossible. This raises questions on the relevance of post-exposure prophylaxis (PEP), particularlyfollowing high-risk household, healthcare-associated, or laboratory exposures, considering itshigh case fatality rate. Ribavirin has demonstrated antiviral activity against hantaviruses in vitroand in animal models, although clinical evidence supporting its use as treatment or PEP forANDV remains extremely limited. The available evidence consists primarily of cell cultureexperiments, Syrian hamster studies, pharmacokinetic and pharmacodynamic extrapolationsfrom other virusses, limited clinical data, and indirect clinical experience with other viralhemorrhagic fevers. This viewpoint summarizes the currently available evidence regardingribavirin as PEP after potential ANDV exposure. We discuss the knowledge gaps that may limitthe applicability of ribavirin PEP, to make informed decisions on the use of ribavirin in thesetting of PEP. Potential dosing strategies are visualized by modeling and simulation, andpotential dose and duration are discussed. Although the biologic rationale for ribavirin PEPappears compelling, the absence of controlled human studies and the potential toxicityassociated with ribavirin currently limit its role to highly selected exposure scenarios and useshortly after exposure.

Background: Chronic infection by Loa loa remains an unsolved immunological paradox. Despite harboring subcutaneously migrating adult worms and often high densities of microfilariae, most patients experience only relatively mild symptoms, yet microfilaricidal treatment can trigger life-threatening inflammation. Here, we investigated innate cell populations hypothesized to play a role in these two faces of the disease, in an endemic population in Gabon. Methodology/Principal findings: We analyzed numbers and activation of eosinophils and basophils, as well as myeloid-derived suppressor cell (MDSC) subsets and associated circulating cytokine levels by flow cytometry in sex- and age-matched L. loa-uninfected (LL-), -amicrofilaraemic (MF-) and -microfilaraemic (MF+) individuals (n = 42), as well as microfilaraemic individuals treated with albendazole (n = 26). The percentage of eosinophils was lower in LL- (3.0%) than in the combined L. loa-infected population, but was similar in MF+ (13.1%) and MF- (12.3%). Upon treatment of MF+, eosinophilia increased from day 0 (17.2%) to day 14 (24.8%) and had decreased below baseline at day 168 (6.3%). Expression of the eosinophil activation marker CD123 followed the same pattern as the percentage of eosinophils, while the inverse was observed for CD193 and to some extent CD125. Circulating IL-5 levels after treatment followed the same pattern as eosinophil dynamics. Basophil numbers did not differ between infection states but increased after treatment of MF+. We did not observe differences in MDSC numbers between infection states or upon treatment. Conclusions/Significance: We demonstrate that both chronic infection and treatment of L. loa microfilaraemia are associated with eosinophil circulation and distinct phenotypical activation markers that might contribute to inflammatory pathways in this setting. In this first ever investigation into MDSC in L. loa infection, we found no evidence for their increased presence in chronic loiasis, suggesting that immunomodulation by L. loa is induced through other pathways.

Background: The stalling global progress in malaria control highlights the need for novel tools for malaria elimination, including transmission-blocking vaccines. Transmission-blocking vaccines aim to induce human antibodies that block parasite development in the mosquito and mosquitoes becoming infectious. The Pfs48/45 protein is a leading Plasmodium falciparum transmission-blocking vaccine candidate. The R0.6C fusion protein, consisting of Pfs48/45 domain 3 (6C) and the N-terminal region of P. falciparum glutamate-rich protein (R0), has previously been produced in Lactococcus lactis and elicited functional antibodies in rodents. Here, we assess the safety and transmission-reducing efficacy of R0.6C adsorbed to aluminium hydroxide with and without Matrix-M™ adjuvant in humans. Methods: In this first-in-human, open-label clinical trial, malaria-naïve adults, aged 18–55 years, were recruited at the Radboudumc in Nijmegen, the Netherlands. Participants received four intramuscular vaccinations on days 0, 28, 56 and 168 with either 30 µg or 100 µg of R0.6C and were randomised for the allocation of one of the two different adjuvant combinations: aluminium hydroxide alone, or aluminium hydroxide combined with Matrix-M1™ adjuvant. Adverse events were recorded from inclusion until 84 days after the fourth vaccination. Anti-R0.6C and anti-6C IgG titres were measured by enzyme-linked immunosorbent assay. Transmission-reducing activity of participants’ serum and purified vaccine-specific immunoglobulin G was assessed by standard membrane feeding assays using laboratory-reared Anopheles stephensi mosquitoes and cultured P. falciparum gametocytes. Results: Thirty-one participants completed four vaccinations and were included in the analysis. Administration of all doses was safe and well-tolerated, with one related grade 3 adverse event (transient fever) and no serious adverse events occurring. Anti-R0.6C and anti-6C IgG titres were similar between the 30 and 100 µg R0.6C arms, but higher in Matrix-M1™ arms. Neat participant sera did not induce significant transmission-reducing activity in mosquito feeding experiments, but concentrated vaccine-specific IgGs purified from sera collected two weeks after the fourth vaccination achieved up to 99% transmission-reducing activity. Conclusions: R0.6C/aluminium hydroxide with or without Matrix-M1™ is safe, immunogenic and induces functional Pfs48/45-specific transmission-blocking antibodies, albeit at insufficient serum concentrations to result in transmission reduction by neat serum. Future work should focus on identifying alternative vaccine formulations or regimens that enhance functional antibody responses. Trial registration: The trial is registered with ClinicalTrials.gov under identifier NCT04862416.

Background A successful malaria vaccine should, depending on the targeted stage of the malaria life cycle, induce both humoral and cellular immune responses. Naturally acquired immunity (NAI) against malaria is thought to target mostly the blood stage and protects individuals against symptomatic and severe disease, but often fails to protect against infection per sé. A better understanding of the mechanisms of NAI and its role in all stages of the life cycle might lead to improved vaccine design of the next-generation malaria vaccine. Methods In Lambaréné, Gabon, a study was conducted in which semi-immune individuals underwent repeated controlled human malaria infections (CHMI) using direct venous inoculation of fully viable cryopreserved Plasmodium falciparum (Pf) sporozoites (PfSPZ, strains NF54 and 7G8). Participants were randomized into two arms allocated 1:1. In arm A, participants were infected using Pf strain 7G8 followed by five infections with Pf strain NF54. In arm B, participants were infected four times with Pf strain NF54 followed by one infection with Pf strain 7G8 and finally one infection with NF54. Here, we investigate the immune response against Pf antigens potentially relevant for the protective immune response against malaria. Selected antigens were expressed using mammalian or bacterial expression systems and subsequently purified. Humoral immune response was assessed by indirect ELISA. Results In total 56 participants were enrolled. Their average age was 28 +/- 6 years. Most participants were male (82%). At baseline, Pf-specific antibodies ranged from 5 to 100 µg/ml in plasma, with a predominance of antibodies against blood stage antigens, such as AMA1 and merozoite surface proteins. The antibody responses against these antigens showed minor fluctuations during follow-up. Conclusion The investigation is ongoing, and further antigens will be investigated. Specifically, the dynamics of antibody responses throughout the study period, also regarding antibody isotype and function, will be presented.

1. This review is written by the developers of Plasmodium falciparum (Pf) sporozoite (SPZ) vaccines (vaccines comprised of live, metabolically active SPZ) and by researchers who have generated the ...

Background: Whole sporozoite immunization under chemoprophylaxis (CPS regime) induces long-lasting sterile homologous protection in the controlled human malaria infection model using Plasmodium falciparum strain NF54. The relative proficiency of liver-stage parasite development may be an important factor determining immunization efficacy. Previous studies show that Plasmodium falciparum strain NF135 produces relatively high numbers of large liver-stage schizonts in vitro. Here, we evaluate this strain for use in CPS immunization regimes. Methods: In a partially randomized, open-label study conducted at the Radboudumc, Nijmegen, the Netherlands, healthy, malaria-naïve adults were immunized by three rounds of fifteen or five NF135-infected mosquito bites under mefloquine prophylaxis (cohort A) or fifteen NF135-infected mosquito bites and presumptive treatment with artemether/lumefantrine (cohort B). Cohort A participants were exposed to a homologous challenge 19 weeks after immunization. The primary objective of the study was to evaluate the safety and tolerability of CPS immunizations with NF135. Results: Relatively high liver-to-blood inocula were observed during immunization with NF135 in both cohorts. Eighteen of 30 (60%) high-dose participants and 3/10 (30%) low-dose participants experienced grade 3 adverse events 7 to 21 days following their first immunization. All cohort A participants and two participants in cohort B developed breakthrough blood-stage malaria infections during immunizations requiring rescue treatment. The resulting compromised immunizations induced modest sterile protection against homologous challenge in cohort A (5/17; 29%). Conclusions: These CPS regimes using NF135 were relatively poorly tolerated and frequently required rescue treatment, thereby compromising immunization efficiency and protective efficacy. Consequently, the full potential of NF135 sporozoites for induction of immune protection remains inconclusive. Nonetheless, the high liver-stage burden achieved by this strain highlights it as an interesting potential candidate for novel whole sporozoite immunization approaches. Trial registration: The trial was registered at ClinicalTrials.gov under identifier NCT03813108.