Biology subjects

Chitnis, N.

Publications and source records attributed to Chitnis, N..

5 recordsLinked to original sources

bioRxiv2026

Contact heterogeneity in network reconstruction: evaluating synthetic graph generators for rabies transmission modeling

Canine rabies remains endemic across much of Africa and Asia, causing approximately 59,000 global deaths yearly. Network-based models that reconstruct contact patterns are central to predicting canine rabies transmission and to designing targeted interventions, but the choice of network generator algorithm may alter network structure and outbreak predictions. We therefore compared five network generators using five empirical free-roaming dog contact networks from Chad, Indonesia, and Guatemala in network topology and outbreak dynamics under susceptible-exposed-infectious-removed (SEIR) and susceptible-infectious-susceptible (SIS) transmission across a range of infectious-period lengths. We found that the degree-corrected stochastic block model (DCSBM) most consistently reproduces both empirical topology and outbreak dynamics, achieving a Mahalanobis distance of 17.6 to the empirical Chad network compared to a range of 21.0 to 220.7 across the other generators and yielding similar results for the other four locations. Moreover, the SIS and SEIR outbreak dynamics reveal that the DCSBM overall best reproduces the simulated empirical outbreak dynamics, but that the consequences of generator choice are not uniform: network reconstruction matters most precisely for short-infectious-window pathogens like canine rabies and progressively less for long-infectious-window pathogens. By an infectious window of nine days, the outbreak dynamics across four of five generators converge to within two percentage points of the empirical reference, even when their underlying topologies differ substantially. This pathogen-dependent sensitivity offers a principled criterion for when generator selection is consequential and when it is not. This work reiterates the importance of both degree heterogeneity and community structure for faithful contact-network reconstruction in canine rabies modeling, particularly for short-window infectious diseases where contact heterogeneity drives transmission. For longer-window pathogens, simpler generators are likely adequate.

ecology↗

bioRxiv2025

Human Skin Model from 15 GHz to 110 GHz

In the recently revised guidelines for electromagnetic safety, basic restrictions expressed in terms of the absorbed power density (APD) at frequencies higher than 6 GHz were introduced. Testing for APD compliance of wireless devices requires experimental and numerical body models or phantoms that conservatively reproduce the absorption characteristics of human skin. Previous studies of APD indicate that frequency-dependent impedance-matching effects are caused by the low-permittivity stratum corneum (SC) layer. The objective of this study is to complement previous work (Christ et al., 2020) and to develop dispersive dielectric models to represent reflection and absorption of electromagnetic fields at the surface of the skin across a frequency range up to 110 GHz. The reflection coefficient of the skin of human volunteers was measured at frequencies of 15 to 43 GHz with open waveguide probes, complementing previous data from 45 to 110 GHz (Christ et al., 2020). The volunteers represented both sexes and different age groups and occupations; measurements were made at various regions of the body. The statistical analysis of the results show that the reflection coefficient follows a normal distribution in regions where the SC is relatively thin, which permits development of a conservative skin model that covers the 95th percentile of the tested population. As expected, in regions where the SC is thicker, e.g., the palms, the reflection coefficient is not normally distributed, because the thickness of the SC depends on the mechanical stress and friction to which the hands are exposed during routine daily activities. There was no evidence of relevant differences due to sex, but there is evidence for a slight age-dependent difference. The measured data - via fitting to the numerical model - allow the derivation of two-layer dielectric dispersive models that represent absorption and reflection at the surface of the skin with known uncertainty. The proposed models can be used to conservatively demonstrate compliance with the APD limits of wireless devices operating at frequencies of up to 110 GHz in any of the 5G and 6G bands defined. HighlightsO_LIbroadband evaluation of the skin reflection coefficient with open waveguide probes; C_LIO_LIcorroboration of increased absorption of millimeter wave radiation in body regions with increased stratum corneum thickness; C_LIO_LIdispersive dielectric models representing reflection and absorption at the skin surface with known population coverage. C_LI

bioengineering↗

bioRxiv2025

Immunity can impose a reproduction-survival tradeoff on human malaria parasites

Many pathogenic organisms produce specialized life stages for within-host multiplication versus on-ward transmission, including malaria parasites. Traits that enable faster multiplication--including limited investment into transmission stage production--should put host health at greater risk (all else equal). Yet it is not clear why parasites do not evolve ever faster multiplication rates, since malaria parasites do not appear to adhere to tradeoffs between the rate and duration of transmission that are classically predicted to constrain parasite evolution. To address this puzzle, we introduce an age-of-infection structured within-host mathematical model incorporating dynamic immune clearance to investigate potential tradeoffs and understand how parasites optimize their transmission investment. When investment is constant across all ages of infection, increased transmission investment reduces infection duration and parasite fitness, with optimal investment occurring at a relatively low value (around 5%), far lower than the optimum recovered from models that lack dynamic feedbacks between parasite investment and immune clearance. For age-varying strategies, our model shows that malaria parasites can enhance their fitness by delaying transmission investment to allow for faster within-host multiplication initially. Our results indicate that adaptive immunity can impose a survival-reproduction tradeoff that explains why malaria parasites cannot evolve ever faster within-host multiplication. Our theoretical framework provides a basis for understanding how transmission investment strategies alter the timing of infectiousness over the lifespan of malaria infections, with implications for parasite evolution in response to control efforts.

evolutionary biology↗

bioRxiv2023

AnophelesModel: An R package to interface mosquito bionomics, human exposure and intervention effects with models of malaria intervention impact

In recent decades, field and semi-field studies of malaria transmission have gathered geographic-specific information about mosquito ecology, behaviour and their sensitivity to interventions. Mathematical models of malaria transmission can incorporate such data to infer the likely impact of vector control interventions and hence guide malaria control strategies in various geographies. To facilitate this process and make model predictions of intervention impact available for different geographical regions, we developed AnophelesModel. AnophelesModel is an online, open-access, R package that directly allows incorporating generated entomological data for adjustment of models to assess intervention scenarios according to species and location-specific characteristics. In addition, it includes a previously published, comprehensive, curated database of field entomological data from over 50 Anopheles species, field data on mosquito and human behaviour, and on estimates of vector control effectiveness. Using the input data, the package parameterizes a discrete-time, state transition model of the mosquito oviposition cycle and infers species-specific impacts of various interventions on vectorial capacity. In addition, it offers formatted outputs ready to use in downstream analyses and by other models of malaria transmission for accurate representation of the vector-specific components. Using AnophelesModel, we show how the key implications for intervention impact change for various vectors and locations. The package facilitates quantitative comparisons of likely intervention impacts in different geographical settings varying in vector compositions, and can thus guide towards more robust and efficient malaria control recommendations. The AnophelesModel R package is available under a GPL-3.0 license at https://github.com/SwissTPH/AnophelesModel.

ecology↗

bioRxiv2023

Inference for entomological semi-field experiments: Fitting a mathematical model assessing personal and community protection of vector-control interventions

The effectiveness of vector-control tools is often assessed by experiments as a reduction in mosquito landings using human landing catches (HLCs). However, HLCs alone only quantify a single characteristic and therefore do not provide information on the overall impacts of the intervention product. Using data from a recent semi-field study which used time-stratified HLCs, aspiration of non-landing mosquitoes, and blood feeding, we suggest a Bayesian inference approach for fitting such data to a stochastic model. This model considers both personal protection, through a reduction in biting, and community protection, from mosquito mortality and disarming (prolonged inhibition of blood feeding). Parameter estimates are then used to predict the reduction of vectorial capacity induced by etofenpox-treated clothing, picaridin topical repellents, transfluthrin spatial repellents and metofluthrin spatial repellents, as well as combined interventions for Plasmodium falciparum malaria in Anopleles minimus. Overall, all interventions had both personal and community effects, preventing biting and killing or disarming mosquitoes. This led to large estimated reductions in the vectorial capacity, with substantial impact even at low coverage. As the interventions aged, fewer mosquitoes were killed; however the impact of some interventions changed from killing to disarming mosquitoes. Overall, this inference method allows for additional modes of action, rather than just reduction in biting, to be parameterised and highlights the tools assessed as promising malaria interventions.

systems biology↗