Biology subjects

Viana, M.

Publications and source records attributed to Viana, M..

10 recordsLinked to original sources

bioRxiv2026

Implications of the trade-offs between negative density-dependence and Allee effects for vector control

BackgroundUnderstanding population dynamics is fundamental to predicting species persistence and extinction, yet remains challenging due to the complex interplay between ecological, environmental and anthropogenic factors. Population dynamics are regulated by intrinsic factors such as negative density-dependence and Allee effects. While negative density-dependence is a well-understood process, Allee effects have received less attention but can have important implications for conservation and species management. For control of disease vectors, negative density-dependence and Allee effects can drive vectors to elimination or to rebound after control. For malaria mosquitoes, negative density-dependence at the larval stages is well known to limit population growth, but the implications of Allee effects and the trade-offs between negative density-dependence and Allee effects remain unknown. It is hypothesised that, depending on the vector control strategy, Allee effects could be triggered and push populations closer to extinction. MethodsA stochastic state-structured population simulation model was developed, which followed a simplified mosquito life cycle. Negative density-dependence and Allee effects were included as parameters influencing larval survival and total fecundity, respectively. The aims were addressed by varying the strength of negative density-dependence and Allee effects parameters, independently and simultaneously, under different vector control scenarios: control, sustained and shorter-term interventions (here, immolating larvicides) that reduced the larval population. ResultsWhile in isolation, the strength of negative density-dependence and Allee effects did not have a long-term impact on the population dynamics, their combination accelerated population extinction as both the strength of negative density-dependence and Allee effects increased. As Allee effects act on small population sizes, sustained interventions were able to activate Allee effects, increasing the probability of population extinction, but short-term interventions can lead to populations rebounding, driven by negative density-dependence. ConclusionUnderstanding less-studied regulatory processes like Allee effects can support vector control by highlighting aspects of the vectors life cycle that are either resilient or vulnerable to interventions. If present, Allee effects could potentially be harnessed to accelerate the elimination of vectors and diseases such as malaria.

ecology↗

bioRxiv2025

Mating behaviour and connectivity drive sporadic European bat lyssavirus 2 infections in Myotis myotis

Gaining insight into the transmission and persistence of zoonoses in wild reservoirs is essential for preventing outbreaks, assessing demographic impacts, and informing conservation strategies. Achieving this requires reliable estimates of key epidemiological parameters, which are governed by aspects of host ecology and behaviour that are notoriously difficult to quantify in many wild species. Taking advantage of a long term study of the ecology of five Greater mouse-eared bats (Myotis myotis) maternity colonies in France ([~]2700 marked individuals), we sought to characterise lyssavirus infection dynamics in a wild bat reservoir. Although no lyssavirus was isolated from any of the 422 saliva samples tested, we report the first indirect evidence of European bat lyssavirus 2 circulation in this species. Interestingly, seropositivity appeared sporadic within colonies (0-100% annually) and synchronized across them, with highest seroprevalence in 2015-2017, but remaining low otherwise. Fitting Bayesian compartmental epidemiological models, we found that shifts in EBLV-2 prevalence were primarily driven by mating season introduction, age-dependant variation in transmission, and frequency-dependent transmission dynamics. Lyssavirus outbreaks involve few deaths overall but can still yield high annual mortality rates. These findings underscore the value of integrating ecological and individual-level data with mechanistic modelling to enhance our understanding and management of zoonotic pathogens in wildlife.

ecology↗

bioRxiv2025

Do epidemiologically impactful vector control interventions disrupt mosquito population structure?

Large epidemiological impacts resulting from disease vector control interventions are typically associated with significant disruption of vector populations. While vector density is a frequently measured response, impacts on demography and connectivity are suspected but rarely quantified. We analysed low-coverage whole-genome sequence data of 893 Anopheles gambiae mosquitoes collected between 2014-2015 during a cluster-randomized control trial (cRCT) in Burkina Faso to compare a pyrethroid-only net (ITN) with a pyrethroid-pyriproxyfen (ITN-PPF) net. Despite reductions of clinical malaria by 12%, and vector density by 22% in the ITN-PPF arm, we found no significant changes in An. gambiae population genetic structure or diversity. We found remarkably low population differentiation, and a lack of discernible clustering by treatment, time, or space. Nucleotide diversity and inbreeding coefficient remained stable between treatments, and genome-wide scans showed no putative signatures of selection between trial arms. These results show that ITN-PPF did not alter An. gambiae genetic structure, possibly due to large, vagile populations in West Africa. More widely, this is first evidence that epidemiologically meaningful reductions in vector density may not impact genetic diversity or connectivity, and challenges what constitutes adequate vector control in large populations.

ecology↗

bioRxiv2024

Dynamics of influenza transmission in vampire bats revealed by longitudinal monitoring and a large-scale anthropogenic perturbation

Interrupting pathogen transmission between species is a priority strategy to mitigate zoonotic threats. However, avoiding counterproductive interventions requires knowing animal reservoirs of infection and the dynamics of transmission within them, neither of which are easily ascertained from the cross-sectional surveys which currently dominate investigations into newly discovered viruses. We used biobanked sera and metagenomic data to reconstruct the transmission of recently discovered bat-associated influenza virus (BIV) over 12 years in three zones of Peru. Mechanistic models fit under a Bayesian framework, which enabled joint inference from serological and molecular data, showed that common vampire bats maintain BIV independently of the currently assumed fruit bat reservoir through immune waning and seasonal transmission pulses. A large-scale vampire bat cull targeting rabies incidentally halved BIV transmission, confirming vampire bats as maintenance hosts. Our results show how combining field studies, perturbation responses and multi-data type models can elucidate pathogen dynamics in nature and reveal pathogen-dependent effects of interventions.

ecology↗

bioRxiv2024

Signatures of adaptation at key insecticide resistance loci in Anopheles gambiae in Southern Ghana revealed by low-coverage WGS.

Resistance to insecticides and adaptation to a diverse range of environments present challenges to Anopheles gambiae s.l. mosquito control efforts in sub-Saharan Africa. Whole-genome-sequencing is often employed for identifying the genomic basis underlying adaptation in Anopheles, but remains expensive for large-scale surveys. Low-coverage whole-genome-sequencing (lcWGS) can identify regions of the genome involved in adaptation at a lower cost, but is currently untested in Anopheles mosquitoes. Here, we use lcWGS to investigate population genetic structure and identify signatures of local adaptation in Anopheles mosquitoes across southern Ghana. In contrast to previous analyses, we find no structuring by ecoregion, with Anopheles coluzzii and Anopheles gambiae populations largely displaying the hallmarks of large, unstructured populations. However, we find signatures of selection at insecticide resistance (IR) loci that appear ubiquitous across ecoregions in An. coluzzii, and strongest in forest ecoregions in An. gambiae. In the IR gene Cyp9k1, we find species-specific alleles under selection, suggesting interspecific variation in the precise mechanism of resistance conferred by Cyp9k1. Our study highlights resistance candidate genes in this region, and validates lcWGS, potentially to very low coverage levels, for population genomics and exploratory surveys for adaptation in Anopheles taxa.

evolutionary biology↗

bioRxiv2023

Mesoscale molecular assembly is favored by the active, crowded cytoplasm

The mesoscale organization of molecules into membraneless biomolecular condensates is emerging as a key mechanism of rapid spatiotemporal control in cells1. Principles of biomolecular condensation have been revealed through in vitro reconstitution2. However, intracellular environments are much more complex than test-tube environments: They are viscoelastic, highly crowded at the mesoscale, and are far from thermodynamic equilibrium due to the constant action of energy-consuming processes3. We developed synDrops, a synthetic phase separation system, to study how the cellular environment affects condensate formation. Three key features enable physical analysis: synDrops are inducible, bioorthogonal, and have well-defined geometry. This design allows kinetic analysis of synDrop assembly and facilitates computational simulation of the process. We compared experiments and simulations to determine that macromolecular crowding promotes condensate nucleation but inhibits droplet growth through coalescence. ATP-dependent cellular activities help overcome the frustration of growth. In particular, actomyosin dynamics potentiate droplet growth by reducing confinement and elasticity in the mammalian cytoplasm, thereby enabling synDrop coarsening. Our results demonstrate that mesoscale molecular assembly is favored by the combined effects of crowding and active matter in the cytoplasm. These results move toward a better predictive understanding of condensate formation in vivo.

biophysics↗

bioRxiv2022

SARS-CoV-2 evolution and patient immunological history shape the breadth and potency of antibody-mediated immunity

Since the emergence of SARS-CoV-2, humans have been exposed to distinct SARS-CoV-2 antigens, either by infection with different variants, and/or vaccination. Population immunity is thus highly heterogeneous, but the impact of such heterogeneity on the effectiveness and breadth of the antibody-mediated response is unclear. We measured antibody-mediated neutralisation responses against SARS-CoV-2Wuhan, SARS-CoV-2, SARS-CoV-2{delta} and SARS-CoV-2o pseudoviruses using sera from patients with distinct immunological histories, including naive, vaccinated, infected with SARS-CoV-2Wuhan, SARS-CoV-2 or SARS-CoV-2{delta}, and vaccinated/infected individuals. We show that the breadth and potency of the antibody-mediated response is influenced by the number, the variant, and the nature (infection or vaccination) of exposures, and that individuals with mixed immunity acquired by vaccination and natural exposure exhibit the broadest and most potent responses. Our results suggest that the interplay between host immunity and SARS-CoV-2 evolution will shape the antigenicity and subsequent transmission dynamics of SARS-CoV-2, with important implications for future vaccine design. Author SummaryNeutralising antibodies provide protection against viruses and are generated because of vaccination or prior infections. The main target of anti-SARS-CoV-2 neutralising antibodies is a protein called Spike, which decorates the viral particle and mediates viral entry into cells. As SARS-CoV-2 evolves, mutations accumulate in the spike protein, allowing the virus to escape antibody-mediated immunity and decreasing vaccine effectiveness. Multiple SARS-CoV-2 variants have appeared since the start of the COVID-19 pandemic, causing various waves of infection through the population and infecting-in some cases-people that had been previously infected or vaccinated. Since the antibody response is highly specific, individuals infected with different variants are likely to have different repertoires of neutralising antibodies. We studied the breadth and potency of the antibody-mediated response against different SARS-CoV-2 variants using sera from vaccinated people as well as from people infected with different variants. We show that potency of the antibody response against different SARS-CoV-2 variants depends on the particular variant that infected each person, the exposure type (infection or vaccination) and the number and order of exposures. Our study provides insight into the interplay between virus evolution and immunity, as well as important information for the development of better vaccination strategies.

microbiology↗

bioRxiv2020

Emergence of Lyme disease on treeless islands in Scotland, UK

Lyme disease (LD) is typically associated with forested habitats but has recently emerged on treeless islands in the Western Isles of Scotland. This has created a need to understand the environmental and human components of LD risk in open habitats. This study quantified both elements of LD risk and compared these between treeless islands with high and low LD incidence. We found high LD incidence was linked to higher prevalence in ticks (6.4% vs 0.4%) and increased human tick bite exposure. Most reported tick bites (72.7%) were within 1km of the home address and commonly in gardens. Residents on islands with high LD incidence reported increasing problems with ticks and suggested changing deer distribution as a potential driver. This study highlights the benefits to public health of an integrated approach to understand the factors contributing to LD emergence and a need to evaluate LD ecology in treeless habitats more broadly.

ecology↗

bioRxiv2020

Predicting the presence and titer of rabies virus neutralizing antibodies from low-volume serum samples in low-containment facilities

Serology is a core component of the surveillance and management of viral zoonoses. Virus neutralization tests are a gold standard serological diagnostic, but requirements for large volumes of serum and high biosafety containment can limit widespread use. Here, focusing on Rabies lyssavirus, a globally important zoonosis, we developed a pseudotype micro-neutralization rapid fluorescent focus inhibition test (pmRFFIT) that overcomes these limitations. Specifically, we adapted an existing micro-neutralization test to use a green fluorescent protein-tagged murine leukemia virus pseudotype in lieu of pathogenic rabies virus, reducing the need for specialized reagents for antigen detection and enabling use in low-containment laboratories. We further used statistical analysis to generate rapid, quantitative predictions of the probability and titer of rabies virus neutralizing antibodies from microscopic imaging of neutralization outcomes. Using 47 serum samples from domestic dogs with neutralizing antibody titers estimated using the fluorescent antibody virus neutralization test (FAVN), pmRFFIT showed moderate sensitivity (78.79%) and high specificity (84.62%). Despite small conflicts, titer predictions were correlated across tests repeated on different dates both for dog samples (r = 0.93), and for a second dataset of sera from wild common vampire bats (r = 0.72, N = 41), indicating repeatability. Our test uses a starting volume of 3.5 L of serum, estimates titers from a single dilution of serum rather than requiring multiple dilutions and end point titration, and may be adapted to target neutralizing antibodies against alternative lyssavirus species. The pmRFFIT enables high-throughput detection of rabies virus neutralizing antibodies in low-biocontainment settings and is suited to studies in wild or captive animals where large serum volumes cannot be obtained.

immunology↗

bioRxiv2018

Prediction of malaria mosquito species and population age structure using mid-infrared spectroscopy and supervised machine learning

Despite the global efforts made in the fight against malaria, the disease is resurging. One of the main causes is the resistance that Anopheles mosquitoes, vectors of the disease, have developed to insecticides. Anopheles must survive for at least 12 days to possibly transmit malaria. Therefore, to evaluate and improve malaria vector control interventions, it is imperative to monitor and accurately estimate the age distribution of mosquito populations as well as total population sizes. However, estimating mosquito age is currently a slow, imprecise, and labour-intensive process that can only distinguish under-from over-four-day-old female mosquitoes. Here, we demonstrate a machine-learning based approach that utilizes mid-infrared spectra of mosquitoes to characterize simultaneously, and with unprecedented accuracy, both age and species identity of females of the malaria vectors Anopheles gambiae and An. arabiensis mosquitoes within their respective populations. The prediction of the age structures was statistically indistinguishable from true modelled distributions. The method has a negligible cost per mosquito, does not require highly trained personnel, is substantially faster than current techniques, and so can be easily applied in both laboratory and field settings. Our results show that, with larger mid-infrared spectroscopy data sets, this technique can be further improved and expanded to vectors of other diseases such as Zika and Dengue.

bioinformatics↗