Biology subjects

Kreppel, K.

Publications and source records attributed to Kreppel, K..

4 recordsLinked to original sources

bioRxiv2024

Larval surveys reveal breeding site preferences of malaria vector Anopheles spp. in Zanzibar City

Malaria is a serious illness that causes over 500,000 deaths annually worldwide, mainly affecting children under five years of age. Tanzania, in Africa, contributes to approximately 4% of those deaths. Malaria is caused by Plasmodium spp. parasites, and it is vectored by mosquitoes in the Anopheles genus. In Zanzibar City, the capital of the Zanzibar archipelago in Tanzania, the incidence of malaria has decreased over the past few decades due to standardized treatment protocols in hospitals and dispensaries and public health interventions targeting adult mosquitoes. However, the incidence remains between 1-2%, with an increasing trend observed over the past few years likely stemming from continued exchange of Plasmodium spp. from other malaria-endemic areas (including mainland Tanzania). While larvicides are a powerful tool to reduce vector populations, this control strategy relies on information on breeding sites and their productivity. In Zanzibar City, no larval surveys have been done in the last few years. Our aim was to characterize Anopheles spp. breeding sites in Zanzibar City during the rainy season. We first conducted systematic larval surveys across 16 semipermanent/permanent water bodies and 30 temporary water bodies. Then, we used Principal Component Analysis and logistic regression to model the effect of physical and chemical parameters, and rainfall on Anopheles presence. We found that Anopheles spp. utilize mostly concrete, semipermanent breeding sites with high levels of dissolved oxygen concentrations but can utilize natural sites after heavy rains. The logistic regression model incorporating rainfall was able to predict the presence of Anopheles larvae with a positive predictive power of 65.7% and a negative predictive power of 88.8%. The data from our study suggest that Anopheles spp. have not yet expanded to using more polluted breeding sites in Zanzibar City (as they have in some mainland locations). These results can inform targeted larvicidal strategies in Zanzibar City.

ecology↗

bioRxiv2022

Plasmid characterization in bacterial isolates of public health relevance in a tertiary healthcare facility in Kilimanjaro, Tanzania

Plasmids are infectious double stranded DNA molecules that are found within bacteria. Horizontal gene transfer promotes successful spread of different types of plasmids within or among bacteria species, making their detection an important task for guiding clinical treatment. We used whole genome sequenced data to determine the prevalence of plasmid replicons in clinical bacterial isolates, the presence of resistance and virulence genes in plasmids, and the relationship between resistance and virulence genes within each plasmid. All bacterial sequences were de novo assembled using Unicycler before extraction of plasmids. Assembly graphs were submitted to Gplas+plasflow for plasmid prediction. The predicted plasmid components were validated using PlasmidFinder. A total of 159 (56.2%) out of 283 bacterial isolates were found to carry plasmids, with E. coli, K. pneumoniae and S. aureus being the most prevalent plasmid carriers. A total of 27 (87.1%) combined plasmids were found to carry both resistance and virulence genes compared to 4 (12.9%) single plasmids. No statistically significant correlation was found between the number of antimicrobial resistance and virulence genes in plasmids (r =-0.25, p > 0.05). Our findings show a relatively high proportion of plasmid-carrying isolates suggesting selection pressure due to antibiotic use in the hospital. Co-occurrence of antibiotic resistance and virulence genes in clinical isolates is a public health relevant problem needing attention.

genomics↗

bioRxiv2022

Development, feasibility and potential effectiveness of community-based continuous mass dog vaccination delivery strategies: lessons for optimization and replication

ObjectivesDog vaccination can eliminate rabies, but annual delivery strategies do not sustain vaccination coverage between campaigns. We describe the development of a community-based continuous mass dog vaccination (CBC-MDV) approach designed to improve and maintain vaccination coverage in Tanzania and examine the feasibility of delivering this approach as well as lessons for its optimization. MethodsWe developed three delivery strategies of CBC-MDV and tested them against the current annual vaccination strategy following the UK MRCs guidance: i) developing an evidence-based theoretical framework of intervention pathways and ii) piloting to test feasibility and inform optimization. For our process evaluation of CBC-MDV we collected data using non-participant observations, meeting reports and implementation audits and in-depth interviews, as well as household surveys of vaccination coverage to assess potential effectiveness. We analyzed qualitative data thematically and quantitative data descriptively. ResultsThe final design included delivery by veterinary teams supported by village-level one health champions. In terms of feasibility, we found that less than half of CBC-MDVs components were implemented as planned. Fidelity of delivery was influenced by the strategy design, implementer availability and appreciation of value intervention components, and local environmental and socioeconomic events (e.g. elections, funerals, school cycles). CBC-MDV activities decreased sharply after initial campaigns, partly due to lack of supervision. Community engagement and involvement was not strong. Nonetheless, the CBC-MDV approaches achieved vaccination coverage above the critical threshold (40%) all-year-round. CBC-MDV components such as identifying vaccinated dogs, which village members work as one health champions and how provision of continuous vaccination is implemented need further optimization prior to scale up. InterpretationCBC-MDV is feasible to deliver and can achieve good vaccination coverage. Community involvement in the development of CBC-MDV, to better tailor components to contextual situations, and improved supervision of activities are likely to improve vaccination coverage in future. AUTHOR SUMMARYAnnual mass dog vaccination campaigns that reach at least 70% of the dog population, should maintain sufficient herd immunity between campaigns to interrupt rabies transmission. However, it is often challenging to reach 70% of the dog population with annual vaccination campaigns. We hypothesized that a community-based continuous approach to dog vaccination could better maintain high levels of vaccination coverage all-year-round. We describe the development of a community-based continuous approach to dog vaccination in Tanzania, and assessed the feasibility of delivering its components, its potential effectiveness and lessons for its optimization. We found that the approach was well accepted, as its development involved key stakeholders. Although less than half of the components of the community-based continuous approach were delivered exactly as planned, over 70% of dogs were vaccinated and the approach maintained coverage above the critical vaccination threshold throughout the year. We conclude that it is feasible to deliver a community-based continuous approach to dog vaccination, but that some components need further improvement; more supervision and community involvement should lead to better outcomes.

immunology↗

bioRxiv2020

Deploying a novel tuberculosis molecular bacterial load assay to assess the elimination rate of Mycobacterium tuberculosis in patients with multidrug-resistant tuberculosis in Tanzania

BackgroundRifampin or multidrug-resistant-tuberculosis (RR/MDR-TB) treatment has transitioned to injectable-free regimens. We tested whether M. tuberculosis (Mtb) elimination rates measured by molecular bacterial load assay (TB-MBLA) in sputa correlate with composition of the RR/MDR-TB antibiotic regimen. MethodsSerial sputa were collected from patients with RR/MDR- and drug-sensitive TB at day 0, 3, 7, 14, and then monthly for 4 months of anti-TB treatment. TB-MBLA was used to quantify viable Mtb 16S rRNA in sputum for estimation of colony-forming-unit per mL (eCFU/mL). Mtb elimination rates were compared among regimens using nonlinear-mixed-effects modeling of repeated measures. ResultsAmong 37 patients with a total of 296 serial sputa; 7 patients received rifampin/isoniazid/pyrazinamide/ethambutol (RHZE), 8 an all-oral bedaquiline-based regimen, 9 an injectable and bedaquiline-containing regimen, and 13 an injectable-containing but bedaquiline-free regimen. The overall mean daily Mtb elimination was -0.24 [95% Confidence-Interval (CI); -0.39 to -0.08)] log10 eCFU/mL, and it varied with treatment-regimen (p < 0.001). Compared to the adjusted Mtb elimination of -0.17 (95% CI; -0.23 to -0.12) for the injectable-containing but bedaquiline-free reference regimen, the elimination rates were -0.62 (95% CI; -1.05 to -0.20) log10 eCFU/mL for the injectable and bedaquiline-containing regimen (p = 0.019), -0.35 (95% CI; -0.65 to -0.13) log10 eCFU/mL for the all-oral bedaquiline-based regimen (p = 0.054), and -0.29 (95% CI; -0.78 to +0.22) log10 eCFU/mL for RHZE (p = 0.332) ConclusionTB-MBLA distinguished Mtb elimination rates in sputa from patients receiving different treatment regimens, suggesting a reliable monitoring tool for RR/MDR-TB, that does not require mycobacterial culture.

microbiology↗