A patchy model for tick population dynamics with patch-specific developmental delays.

Tick infestation and tick-borne disease spread in a region of multiple adjacent patches with different environmental conditions depend heavily on the host mobility and patch-specific suitability for tick growth. Here we introduce a two-patch model where environmental conditions differ in patches and yield different tick developmental delays, and where feeding adult ticks can be dispersed by the movement of larger mammal hosts. We obtain a coupled system of four delay differential equations with two delays, and we examine how the dynamical behaviours depend on patch-specific basic reproduction numbers and host mobility by using singular perturbation analyses and monotone dynamical systems theory. Our theoretical results and numerical simulations provide useful insights for tick population control strategies.

Variant-specific interventions to slow down replacement and prevent outbreaks.

Emergency and establishment of variants of concern (VOC) impose significant challenges for the COVID-19 pandemic control specially when a large portion of the population has not been fully vaccinated. Here we develop a mathematical model and utilize this model to examine the impact of non pharmaceutical interventions, including the COVID-test (PCR, antigen and antibody test) and whole genome sequencing (WGS) test capacity and contact tracing and quarantine strength, on the VOC-induced epidemic wave. We point out the undesirable and unexpected effect of lukewarm tracing and quarantine that can potentially increase the VOC-cases at the outbreak peak time, and we demonstrate the significance of strain-specific interventions to either prevent a VOC-induced outbreak, or to mitigate the epidemic wave when this outbreak is unavoidable.

Are host control strategies effective to eradicate tick-borne diseases (TBD)?

Ticks are responsible for spreading harmful diseases including Lyme disease and tick-borne encephalitis. Understanding tick population dynamics and predicting risk of tick-borne disease insurgence helps to design preventive actions against the disease spread. Using a compartmental model describing the pathogen transmission among ticks and hosts, we study the influence of host-targeted tick control strategies with chemical insecticides on tick population and disease transmission dynamics. Our analysis shows that in areas with rapid-growing population of ticks, host-targeted controls using chemical insecticides may enhance disease persistence and even turn a disease-free area to a disease endemic area. Therefore, the complex dynamics of pathogen spread among ticks and hosts should be carefully examined when designing tick control strategies.

Complexity dynamics and simulations in a discrete switching ecosystem induced by an intermittent threshold control strategy.

Pest control is a worldwide challenge. An approach that has been developed to meet this challenge is the integrated pest management (IPM) strategy, which aims to offer environmentally sensitive solutions to pest problems, and takes into account the complex dynamics involved in the design of controlling pests. In this paper, we propose a discrete switching host-parasitoid model with a threshold control strategy, meanwhile, provide some qualitative analyses of the complexity of dynamic behaviors of the model that includes single and multi-parameter bifurcations and chaos. Furthermore, we do some numerical bifurcations and parameter sensibility analysis, revealing how the key control parameters and initial interaction state between the two populations affect pest control, as well as the dynamical balance between of the hosts and parasitoids. The model and analytical techniques developed in this work could be applied in other settings relevant to threshold control strategies.

Ordinary surface ECG electrodes accurately reflect cardiac electric activity at hypothermia.

BACKGROUND: It has been claimed that needle electrodes can be a useful means to detect weak ECG signals in cases of accidental hypothermia. METHODS: Four pigs were cooled by immersion in ice water, followed by direct cooling of the blood through an extracorporeal circulation system until the core temperature was lowered to 12 degrees C and surface-measured ECG indicated asystole. Following cooling, the pigs were rewarmed and weaned from extracorporeal circulation if possible. ECG and interelectrode impedance were measured between surface electrodes, needle electrodes and electrodes sewn to the epicardium during the cooling and rewarming procedure. RESULTS: Needle and surface electrodes showed exactly the same ECG whatever the temperature of the skin or the core was. The impedance varied only slightly with temperature and could not explain the disappearance of surface ECG. The QRS wave amplitude showed the greatest sensitivity to temperature, disappearing completely before the P-wave disappeared. The P-wave showed the least sensitivity, and was the last wave to disappear, indicating that the sinus node is the most resistant part of the heart to cooling. Between 19 and 17 degrees C, a commercial monitor indicated asystole although P-waves could be seen in the ECG and atrial contractions could be visually observed on the heart. CONCLUSION: Surface electrodes had a similar high accuracy to indicate electric activity as needle electrodes. Higher amplification and reduction of the timebase made it possible to detect ECG in a situation where asystole was indicated by commercial monitors.

A comparative study of three techniques for diameter selective fiber activation in the vagal nerve: anodal block, depolarizing prepulses and slowly rising pulses.

The paper shows selective smaller fiber activation in the left and right vagal nerve in in vivo experiments in pigs using three different techniques: anodal block, depolarizing prepulses and slowly rising pulses. All stimulation techniques were performed with the same experimental setup. The techniques have been compared in relation to maximum achievable suppression of nerve activity, maximum required current, maximum achievable stimulation frequency and the required charge per phase. Suppression of the largest fiber activity (expressed as a percentage of the maximum response) was 0-40% for anodal block, 10-25% for depolarizing prepulses and 40-50% for slowly rising pulses (duration up to 5 ms). Incomplete suppression of activation was mainly attributed to the large size of the vagal nerve (3.0-3.5 mA) which resulted in a large difference of the excitation thresholds of nerve fibers at different distances from the electrode, as well as a relatively short duration of slowly rising pulses. The technique of anodal block required the highest currents. The techniques of slowly rising pulses and anodal block required comparable charge per phase that was larger than for the technique of depolarizing prepulses. Depolarizing prepulses were an optimal choice regarding maximum required current and charge per phase but were very sensitive to small changes of the current amplitude. The other two techniques were more robust regarding small changes of stimulation parameters. The maximum stimulation frequency, using typical values of stimulation parameters, was 105 Hz for depolarizing prepulses, 30 Hz for anodal block and 28 Hz for slowly rising pulses. Only a technique of depolarizing prepulses had a charge per phase within the safe limits. For the other two techniques it would be necessary to optimize the shape of a stimulation pulse in order to reduce the charge per phase.

Closed-loop control of the heart rate by electrical stimulation of the vagus nerve.

Stimulation of the vagus nerve potentially decreases the risk of sudden cardiac death. An improvement of the technique would be its regulation using the heart rate (HR) as a feedback variable. We address the possibility of closed-loop control of the HR, focusing on the stimulation parameters, nerve fibre populations and the reproducibility of the cardiovascular response. The response to electrical stimulation of the vagus nerve was studied in seven acute experiments on pigs. Feedback regulation of the HR over periods of 5 min was carried out. Three main populations of myelinated fibres were found. The performance of the controller was significantly better at amplitudes higher than those needed for stimulation of the myelinated components only. A 18% change in the duration of the RR interval could be controlled in all experiments. The possibility of closed-loop control of the HR seems to be promising.