scholarly journals Detection, not mortality, constrains the evolution of virulence

2021 ◽  
Author(s):  
David A Kennedy
Keyword(s):  
Mathematical Model ◽  
Disease Severity ◽  
Behavioral Change ◽  
Scientific Literature ◽  
Empirical Support ◽  
Infectious Period ◽  
Trade Off ◽  
Evolution Of Virulence ◽  
Host Mortality

Why would a pathogen evolve to kill its hosts when killing a host ends a pathogen's own opportunity for transmission? A vast body of scientific literature has attempted to answer this question using "trade-off theory," which posits that host mortality persists due to its cost being balanced by benefits of other traits that correlate with host mortality. The most commonly invoked trade-off is the mortality-transmission trade-off, where increasingly harmful pathogens are assumed to transmit at higher rates from hosts while the hosts are alive, but the pathogens truncate their infectious period by killing their hosts. Here I show that costs of mortality are too small to plausibly constrain the evolution of disease severity except in systems where survival is rare. I alternatively propose that disease severity can be much more readily constrained by a cost of behavioral change due to the detection of infection, whereby increasingly harmful pathogens have increasing likelihood of detection and behavioral change following detection, thereby limiting opportunities for transmission. Using a mathematical model, I show the conditions under which detection can limit disease severity. Ultimately, this argument may explain why empirical support for trade-off theory has been limited and mixed.

scholarly journals Updated overview on the interplay between obesity and COVID-19

Diagnosis ◽  
2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Diletta Onorato ◽  
Giovanni Carpenè ◽  
Giuseppe Lippi ◽  
Mairi Pucci
Keyword(s):  
Disease Severity ◽  
Clinical Characteristics ◽  
Literature Search ◽  
Scientific Literature ◽  
Population Sample ◽  
Obese Patients ◽  
Health Crisis ◽  
Keywords Obesity ◽  
Negative Prognostic Factor ◽  
The Impact

AbstractThe worldwide spread of coronavirus disease 2019 (COVID-19) has generated a global health crisis and more than a million deaths so far. Epidemiological and clinical characteristics of COVID-19 are increasingly reported, along with its potential relationship with overweight and/or obesity. Therefore, we aim here to review the current scientific literature on the impact of overweight and/or obesity among hospitalized patients who have developed severe or critical forms of COVID-19. Following PRISMA guidelines, our literature search identified over 300 scientific articles using the keywords “obesity” and “COVID-19”, 22 of which were finally selected for reporting useful information on the association between overweight/obesity and disease severity. In particular, in 11 out of the 14 studies (79%) which evaluated the association between obesity and disease severity providing also a risk estimate (i.e., the odd ratio; OR), the OR value was constantly >2. Although the studies were found to be heterogeneous in terms of design, population, sample size and endpoints, in most cases a significant association was found between obesity and the risk of progressing to severe COVID-19 illness, intensive care unit admission and/or death. We can hence conclude that an increased body mass index shall be considered a negative prognostic factor in patients with COVID-19, and more aggressive prevention or treatment shall hence be reserved to overweight and/or obese patients.

scholarly journals Parasite variation and the evolution of virulence in a Daphnia-microparasite system

Parasitology ◽  
2007 ◽  
Vol 135 (3) ◽  
pp. 303-308 ◽  
Author(s):  
T. J. LITTLE ◽  
W. CHADWICK ◽  
K. WATT
Keyword(s):  
Genetic Variation ◽  
Rank Order ◽  
Genetic Relationships ◽  
Natural Populations ◽  
Host Genotype ◽  
Relative Growth ◽  
Trade Off ◽  
Relative Growth Rates ◽  
Pasteuria Ramosa ◽  
Evolution Of Virulence

SUMMARYUnderstanding genetic relationships amongst the life-history traits of parasites is crucial for testing hypotheses on the evolution of virulence. This study therefore examined variation between parasite isolates (the bacterium Pasteuria ramosa) from the crustacean Daphnia magna. From a single wild-caught infected host we obtained 2 P. ramosa isolates that differed substantially in the mortality they caused. Surprisingly, the isolate causing higher early mortality was, on average, less successful at establishing infections and had a slower growth rate within hosts. The observation that within-host replication rate was negatively correlated with mortality could violate a central assumption of the trade-off hypothesis for the evolution of virulence, but we discuss a number of caveats which caution against premature rejection of the trade-off hypothesis. We sought to test if the characteristics of these parasite isolates were constant across host genotypes in a second experiment that included 2 Daphnia host clones. The relative growth rates of the two parasite isolates did indeed depend on the host genotype (although the rank order did not change). We suggest that testing evolutionary hypotheses for virulence may require substantial sampling of both host and parasite genetic variation, and discuss how selection for virulence may change with the epidemiological state of natural populations and how this can promote genetic variation for virulence.

Design of Control of DC Motor

2014 ◽  
Vol 611 ◽  
pp. 325-331
Author(s):  
Ľubica Miková ◽  
Michal Kelemen ◽  
Vladislav Maxim ◽  
Jaromír Jezný
Keyword(s):  
Mathematical Model ◽  
Virtual Environment ◽  
Computer Technology ◽  
Current Practice ◽  
Scientific Literature ◽  
Model Simulation ◽  
Graphical Interface ◽  
Dc Motors ◽  
Matlab Program ◽  
Simulation Results

In current practice the use of mathematical models is substantially widespread, reason being the recent increase in development of programs for this purpose, with the option of model simulation in a virtual environment, proportional to the evolving computer technology. The article contains a mathematical model created using Matlab program. The simulation results are compared with scientific literature that addresses DC motors and evaluated. For simplicity, a graphical interface was created.

scholarly journals Optimization of Stochastic Lossy Transport Networks and Applications to Power Grids

2021 ◽  
Author(s):  
Alessandro Zocca ◽  
Bert Zwart
Keyword(s):  
Mathematical Model ◽  
Renewable Energy ◽  
Smart Grids ◽  
Transport Network ◽  
Power Grids ◽  
Performance Gain ◽  
Power Losses ◽  
Transport Networks ◽  
Trade Off ◽  
Stochastic Load

Motivated by developments in renewable energy and smart grids, we formulate a stylized mathematical model of a transport network with stochastic load fluctuations. Using an affine control rule, we explore the trade-off between the number of controllable resources in a lossy transport network and the performance gain they yield in terms of expected power losses. Our results are explicit and reveal the interaction between the level of flexibility, the intrinsic load uncertainty, and the network structure.

scholarly journals Empirical support for the mathematical model of water deaeration in the centrifugal-vortex deaerators

Vestnik IGEU ◽  
2015 ◽  
pp. 5-10
Author(s):  
G.V. Leduhovsky ◽  
◽  
A.N. Roslyakov ◽  
V.N. Vinogradov ◽  
V.P. Zhukov ◽  
...  
Keyword(s):  
Mathematical Model ◽  
Empirical Support ◽  
The Mathematical Model ◽  
Water Deaeration

scholarly journals The evolution of constitutive and induced defences to infectious disease

2018 ◽  
Vol 285 (1883) ◽  
pp. 20180658 ◽  
Author(s):  
Mike Boots ◽  
Alex Best
Keyword(s):  
Infectious Disease ◽  
Infectious Period ◽  
Induced Defence ◽  
Trade Off ◽  
Disease Mortality ◽  
Induced Defences ◽  
High Virulence ◽  
Constitutive Defence ◽  
Very High

In response to infectious disease, hosts typically mount both constitutive and induced defences. Constitutive defence prevents infection in the first place, while induced defence typically shortens the infectious period. The two routes to defence, therefore, have very different implications not only to individuals but also to the epidemiology of the disease. Moreover, the costs of constitutive defences are likely to be paid even in the absence of disease, while induced defences are likely to incur the most substantial costs when they are used in response to infection. We examine theoretically the evolutionary implications of these fundamental differences. A key result is that high virulence in the parasite typically selects for higher induced defences even if they result in immunopathology leading to very high disease mortality. Disease impacts on fecundity are critical to the relative investment in constitutive and induced defence with important differences found when parasites castrate their hosts. The trade-off between constitutive and induced defence has been cited as a cause of the diversity in defence, but we show that the trade-off alone is unlikely to lead to diversity. Our models provide a framework to examine relative investment in different defence components both experimentally and in the field.

scholarly journals Modeling behavioral change and COVID-19 containment in Mexico: A trade-off between lockdown and compliance

2020 ◽  
Vol 325 ◽  
pp. 108370 ◽  
Author(s):  
Manuel Adrian Acuña-Zegarra ◽  
Mario Santana-Cibrian ◽  
Jorge X. Velasco-Hernandez
Keyword(s):  
Behavioral Change ◽  
Trade Off

WITHIN-HOST PARASITE DYNAMICS, EMERGING TRADE-OFF, AND EVOLUTION OF VIRULENCE WITH IMMUNE SYSTEM

Evolution ◽  
2003 ◽  
Vol 57 (7) ◽  
pp. 1489 ◽  
Author(s):  
Jean-Baptiste André ◽  
Jean-Baptiste Ferdy ◽  
Bernard Godelle
Keyword(s):  
Immune System ◽  
Trade Off ◽  
Evolution Of Virulence ◽  
Host Parasite ◽  
Parasite Dynamics
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