From resistance to persistence: Insights of a mathematical model on the indiscriminate use of insecticide.

The development of insecticide resistance is becoming a threat to many arboviruses control programs worldwide. While this has been attributed to the indiscriminate use of insecticide, a more theoretical study is apparently not available. Using in-silico experiments, we investigated the effects of two different policies: one used by the Brazilian Ministry of Health (which follows the World Health Organization protocol) and a more permissive one, akin to those employed by various gated communities and private companies. The results show that the public policy does not lead to resistance fixation. On the other hand, permissive application of adulticide, such as intensive domestic use mainly during epidemic periods, might lead to the fixation of a resistant population, even when resistance is associated with moderate fitness costs.

Costly Inheritance and the Persistence of Insecticide Resistance in Aedes aegypti Populations.

Global emergence of arboviruses is a growing public health concern, since most of these diseases have no vaccine or prevention treatment available. In this scenario, vector control through the use of chemical insecticides is one of the most important prevention tools. Nevertheless, their effectiveness has been increasingly compromised by the development of strong resistance observed in field populations, even in spite of fitness costs usually associated to resistance. Using a stage-structured deterministic model parametrised for the Aedes aegypti--the main vector for dengue--we investigated the persistence of resistance by studying the time for a population which displays resistance to insecticide to revert to a susceptible population. By means of a comprehensive series of in-silico experiments, we studied this reversal time as a function of fitness costs and the initial presence of the resistance allele in the population. The resulting map provides both a guiding and a surveillance tool for public health officers to address the resistance situation of field populations. Application to field data from Brazil indicates that reversal can take, in some cases, decades even if fitness costs are not small. As by-products of this investigation, we were able to fit very simple formulas to the reversal times as a function of either cost or initial presence of the resistance allele. In addition, the in-silico experiments also showed that density dependent regulation plays an important role in the dynamics, slowing down the reversal process.

Quasi-static and cyclic compressive loading studies of the intervertebral disc with combined flexion and torsion / Estudo da compressão monotônica e cíclica associada à flexão e torção do disco intervertebral

Bovine caudal motion segments were used to investigate the loss of load-bearing ability of the intervertebral disc (IVD) under both quasi-static and cyclic compressive loading combined with torsion and flexion. While the response of the disc to both compressive hyper-flexion and hyper-torsion has been previously investigated much less is known about their individual and combined influence on compressive failure. Eighty motion segments dissected from 41 bovine tails were subjected to quasi-static and cyclic compression with added components of flexion and torsion. The four different combinations of flexion and torsion were 0º torsion/0º flexion, 10º torsion/15º flexion, 10º torsion/0º flexion and 0º torsion/15º flexion. Quasi-static compression failed to show any significant difference among the different combinations of torsion and flexion for failure stress, failure strain and compressive tangent modulus. Cyclic compression indicated a significant influence of torsion in reducing the disc's load-bearing ability. Cyclic loading provides a more sensitive tool for the assessment of potentially damaging mechanical parameters for the IVD.

Segmentos de cauda bovina foram utilizados para investigar a perda de capacidade de suporte de carga do disco intervertebral (IVD) sob compressão monotônica e cíclica combinada com torção e flexão. Embora a resposta do disco a hiper-flexão e hiper-torção compressiva já fora previamente investigada, pouco se conhece sobre suas influências individuais e combinada para a falha compressiva. Oitenta segmentos dissecados a partir de 41 caudas bovina foram submetidos a compressão monotônica e cíclica com componentes adicionais de flexão e de torção. As quatro combinações diferentes de flexão e torção foram 0º torção/0º flexão, 10º torção/15º flexão, 10º torção/0º flexão e 0º torção/15º flexão. A compressão monotônica não evidenciou qualquer diferença significativa entre as diferentes combinações de torção e flexão para tensão de ruptura, deformação em ruptura e módulo tangente. A compressão cíclica indicou influência significativa da torção na redução da capacidade de carga do disco intervertebral. A carga cíclica proporciona uma ferramenta sensível para a avaliação de parâmetros mecânicos potencialmente deletérios ao IVD.

Mechanisms of anular failure resulting from excessive intradiscal pressure: a microstructural-micromechanical investigation.

STUDY DESIGN: Microstructural/micromechanical investigation of pathways of anular wall disruption. OBJECTIVE: To investigate the fundamental mechanisms by which both intralamellar and interlamellar relationships are disrupted by nuclear pressurization. SUMMARY OF BACKGROUND DATA: Understanding how anular failure might occur following increased nuclear pressurization requires an experimental approach that avoids artifactual injury to the anulus but reveals structural disruption resulting directly from the pressurization event. METHODS: Bovine motion segments were subjected to internal pressurization using a novel "through vertebra" gel injection method. Intralamellar and interlamellar sections were deliberately chosen so as to expose systematic patterns of structural disruption resulting from the pressurization event. This microdisruption was investigated using a novel method that combined microtensile manipulation and simultaneous differential contrast imaging of the fully hydrated unstained sections. RESULTS: The inner anulus was most severely disrupted, the middle regions developed a series of regular clefts along axes of weakness within the in-plane arrays, with only mild array disruption occurring in the outer regions. CONCLUSIONS: A mechanism is proposed whereby an anular failure pathway, driven by hydrostatic nuclear pressure, could track through the complex anular structures via a set of disruptive events causing weakening of both the in-plane and interlamellar junction interconnections.

Failure strength of the bovine caudal disc under internal hydrostatic pressure.

The structure of the disc is both complex and inhomogeneous, and it functions as a successful load-bearing organ by virtue of the integration of its various structural regions. These same features also render it impossible to assess the failure strength of the disc from isolated tissue samples, which at best can only yield material properties. This study investigated the intrinsic failure strength of the intact bovine caudal disc under a simple mode of internal hydrostatic pressure. Using a hydraulic actuator, coloured hydrogel was injected under monitored pressure into the nucleus through a hollow screw insert which passed longitudinally through one of the attached vertebrae. Failure did not involve vertebra/endplate structures. Rather, failure of the disc annulus was indicated by the simultaneous manifestation of a sudden loss of gel pressure, a flood of gel colouration appearing in the outer annulus and audible fibrous tearing. A mean hydrostatic failure pressure of 18+/-3 MPa was observed which was approximated as a thick-wall hoop stress of 45+/-7 MPa. The experiment provides a measurement of the intrinsic strength of the disc using a method of internal hydrostatic loading which avoids any disruption of the complex architecture of the annular wall. Although the disc in vivo is subjected to a much more complex pattern of loading than is achieved using simple hydrostatic pressurization, this latter mode provides a useful tool for investigating alterations in intrinsic disc strength associated with prior loading history or degeneration.

Histoarchitecture of schistosomal granuloma development and involution: morphogenetic and biomechanical approaches

The authors present morphogenetic and biomechanical approaches on the concept of the Schistosoma mansoni granulomas, considering them as organoid structures that depend on cellular adhesion and sorting, forming rearrangement into hierarchical concentric layers, creating tension-dependent structures, aiming to acquire round form, since this is the minimal energy form, in which opposing forces pull in equally from all directions and are in balance. From the morphogenetic point of view, the granulomas function as little organs, presenting maturative and involutional stages in their development with final disappearance (pre-granulomatous stages, subdivided in: weaky and/or initial reactive and exudative; granulomatous stages: exudative-productive, productive and involutional). A model for the development of granulomas was suggested according to the following stages: encapsulating, focal hystolysis, fiber production, orientation and compacting and involution and desintegration. The autors concluded that schistosomal granuloma is not a tangled web of individual cells and fibers, but an organized structure composed by host and parasite components, which is not formed to attack the miracidia, but functions as an hybrid interface between two different phylogenetic beings.

Efeitos de danos por fadiga nos parâmetros mecânicos de tendöes humanos / Effects of damages to fatigue in mechanical parameters of human tendon

Ensaios de tração, caracterização dinâmica e testes de fadiga de tendões humanos foram realizados com o uso de garras especialmente desenhadas e medição local da área de secção. Caracterização dinâmica de espécimes do tendão Extensor digitorum longus (EDL) do membro inferior foi efetuada anteriormente e posteriormente a teste de fadiga mecânica parcial. Estes espécimes também foram submetidos a ensaio de tração. Os efeitos de dano fadiga nos parâmetros mecânicos foram investigados através de um índice de dano.

Abstract - Quasi-static tensile test. dynamic characterisation and fatigue testing of human tendons were accomplished with the use of specially designed grips and the local measurement of the cross-sectional area. Specimens of Extensor digitorum longus (EDL) tendons of the foot were subjected to dynamic characterisation prior and after partia! mechanical fatigue. Specimens were also subjected to quasi-static tensile testing. The effect of fatigue damage on mechanical parameters was investigated by means of a damage ratio