scholarly journals If we cannot eliminate them, should we tame them? Mathematics underpinning the dose effect of virus infection and its application on covid-19 virulence evolution

2021 ◽  
Author(s):  
Zhaobin Xu ◽  
Hongmei Zhang
Keyword(s):  
Virus Infection ◽  
Population Density ◽  
Turning Point ◽  
Host Population ◽  
Infection Process ◽  
Dose Effect ◽  
Sigmoid Function ◽  
Protection Measures ◽  
Inoculum Dose ◽  
Function Relationship

There is a dose effect in the infection process, that is, different initial virus invasion loads will lead to nonlinear changes in infection probability. Experiments already proved that there was a sigmoid functional relationship between virus infection probability and inoculum dose. By means of mathematical simulation of stochastic process, we theoretically demonstrate that there is a sigmoid function relationship between them. At the same time, our model found three factors that influence the severity of infection symptoms, those are virus toxicity, virus invasion dose and host immunity respectively. Therefore, the mortality rate cannot directly reflect the change of virus toxicity, but is the result of the comprehensive action of these three factors. Protective measures such as masks can effectively reduce the severity of infection while reducing the probability of infection. Based on the sigmoid function relationship between virus infection probability and initial virus invasion dose, we deduce that for highly infectious viruses, such as SARS-COV-2, the evolution of its toxicity is closely related to the host population density, and its toxicity will first increase and then decrease with the increase of host population density. That is to say, on the basis of extremely low host population density, increasing population density is beneficial to the development of virus towards strong toxicity. However, this trend is not sustainable, and there is a turning point of population density. Beyond this turning point, increasing population density will be beneficial to the development of virus towards weak toxicity. This theory can well explain the differences of mortality in Covid-19 in different countries. Countries with high population density and extremely low population density often correspond to lower mortality, while countries with population density in the range of 20-100/km2 often have higher mortality. At the same time, we propose that social distance and masks can effectively accelerate the evolution of virus towards low toxicity, so we should not give up simple and effective protection measures while emphasizing vaccination.

scholarly journals Effects of heterogeneity in infection-exposure history and immunity on the dynamics of a protozoan parasite

2007 ◽  
Vol 4 (16) ◽  
pp. 841-849 ◽  
Author(s):  
Maite Severins ◽  
Don Klinkenberg ◽  
Hans Heesterbeek
Keyword(s):  
Dynamic Behaviour ◽  
Protozoan Parasite ◽  
Host Population ◽  
Infection Process ◽  
Control Measures ◽  
Complex Dynamic ◽  
Systems Models ◽  
Exposure History ◽  
The Relationship ◽  
Initial Contamination

Infection systems where traits of the host, such as acquired immunity, interact with the infection process can show complex dynamic behaviour with counter-intuitive results. In this study, we consider the traits ‘immune status’ and ‘exposure history’, and our aim is to assess the influence of acquired individual heterogeneity in these traits. We have built an individual-based model of Eimeria acervulina infections, a protozoan parasite with an environmental stage that causes coccidiosis in chickens. With the model, we simulate outbreaks of the disease under varying initial contaminations. Heterogeneity in the traits arises stochastically through differences in the dose and frequency of parasites that individuals pick up from the environment. We find that the relationship between the initial contamination and the severity of an outbreak has a non-monotonous ‘wave-like’ pattern. This pattern can be explained by an increased heterogeneity in the host population caused by the infection process at the most severe outbreaks. We conclude that when dealing with these types of infection systems, models that are used to develop or evaluate control measures cannot neglect acquired heterogeneity in the host population traits that interact with the infection process.

Parasite infection and host dynamics in a naturally fluctuating rodent population

2012 ◽  
Vol 90 (9) ◽  
pp. 1149-1160 ◽  
Author(s):  
J.C. Winternitz ◽  
M.J. Yabsley ◽  
S.M. Altizer
Keyword(s):  
Population Density ◽  
Experimental Studies ◽  
Host Density ◽  
Positive Association ◽  
Population Cycles ◽  
Host Population ◽  
Reproductive Status ◽  
Vole Cycles ◽  
Host Infection ◽  
The Impact

Parasites can both influence and be affected by host population dynamics, and a growing number of case studies support a role for parasites in causing or amplifying host population cycles. In this study, we examined individual and population predictors of gastrointestinal parasitism on wild cyclic montane voles ( Microtus montanus (Peale, 1848)) to determine if evidence was consistent with theory implicating parasites in population cycles. We sampled three sites in central Colorado for the duration of a multiannual cycle and recorded the prevalence and intensity of directly transmitted Eimeria Schneider, 1875 and indirectly transmitted cestodes from a total of 267 voles. We found significant associations between host infection status, individual traits (sex, age, and reproductive status) and population variables (site, trapping period, and population density), including a positive association between host density and cestode prevalence, and a negative association between host density and Eimeria prevalence. Both cestode and Eimeria intensity correlated positively with host age, reproductive status, and population density, but neither parasite was associated with poorer host condition. Our findings suggest that parasites are common in this natural host, but determining their potential to influence montane vole cycles requires future experimental studies and long-term monitoring to determine the fitness consequences of infection and the impact of parasite removal on host dynamics.

Heterogeneous population dynamics of active particles: Progression, mutations, and selection dynamics

2017 ◽  
Vol 27 (04) ◽  
pp. 617-640 ◽  
Author(s):  
L. Gibelli ◽  
A. Ełaiw ◽  
M. A. Alghamdi ◽  
A. M. Althiabi
Keyword(s):  
Population Dynamics ◽  
Immune System ◽  
Virus Infection ◽  
Mathematical Structure ◽  
Infection Process ◽  
Heterogeneous Population ◽  
Cellular Aging ◽  
Active Particles ◽  
Selection Dynamics ◽  
Classical Models

This paper proposes a conceptual revisiting of population dynamics to include heterogeneous behaviors of individuals, mutations, and selection. The first part of the paper focuses on the derivation of a general mathematical structure which permits to describe systems composed of individuals whose interactions are stochastic. Hybrid models where some of the populations follow a deterministic dynamics are also discussed. The second part deals with two specific applications, namely the effect of the cellular aging in the virus infection process and the dynamics of virus mutation and competition with the immune system. Sample simulations are presented and classical models of population dynamics are critically analyzed in light of the proposed approach.

Apoptosis and autophagy as a turning point in viral–host interactions: the case of human norovirus and its surrogates

2020 ◽  
Author(s):  
Sean Kennedy ◽  
Mélanie M Leroux ◽  
Alexis Simons ◽  
Brice Malve ◽  
Marc Devocelle ◽  
...  
Keyword(s):  
Viral Entry ◽  
Turning Point ◽  
Infection Process ◽  
Host Interactions ◽  
Antiviral Therapies ◽  
Leading Role ◽  
Host Interaction ◽  
Major Response ◽  
Causes Of Disease ◽  
Viral Host Interactions

Human gastroenteritis viruses are amid the major causes of disease worldwide, responsible for more than 2 million deaths per year. Human noroviruses play a leading role in the gastroenteritis outbreaks and the continuous emergence of new strains contributes to the significant morbidity and mortality. Many aspects of the viral entry and infection process remain unclear, including the major response of the host cell to the virus, which is the trigger of several programmed cell death related mechanisms. In this review, we assessed apoptosis and autophagy at various stages in the infection process to provide better understanding of the viral–host interaction. This brings us closer to fully understanding how noroviruses work, thus allowing the development of specific antiviral therapies.

Fish population size, and not density, as the determining factor of parasite infection: a case study

Parasitology ◽  
2004 ◽  
Vol 128 (3) ◽  
pp. 305-313 ◽  
Author(s):  
A. M. BAGGE ◽  
R. POULIN ◽  
E. T. VALTONEN
Keyword(s):  
Species Richness ◽  
Population Density ◽  
Population Size ◽  
Fish Population ◽  
Host Population ◽  
Fish Length ◽  
Total Fish ◽  
Infection Parameters ◽  
The Mean

The diversity and abundance of parasites vary widely among populations of the same host species. These infection parameters are, to some extent, determined by characteristics of the host population or of its habitat. Recent studies have supported predictions derived from epidemiological models regarding the influence of host population density: parasite abundance and parasite species richness are expected to increase with increasing host population density, at least for directly transmitted parasites. Here, we test this prediction using a natural system in which populations of the crucian carp, Carassius carassius (L.), occur alone, with no other fish species, in a series of 9 isolated ponds in Finland. The ectoparasite communities in these fish populations consist of only 4 species of monogeneans (Dactylogyrus formosus, D. wegeneri, D. intermedius and Gyrodactylus carassii); the total and relative abundance of these 4 species varies among ponds, with one or two of the species missing from certain ponds. Across ponds, only one factor, total fish population size, explained a significant portion of the variance in both the mean number of monogenean species per fish and the mean total abundance of monogenean individual per fish. In contrast, fish population density did not influence either monogenean abundance or species richness, and neither did any of the other variables investigated (mean fish length per pond, number of fish examined per pond, distance to the nearest lake, and several water quality measures). In our system, proximity among fish individuals (i.e. host population density) may not be relevant to the proliferation of monogeneans; instead, the overall availability of host individuals in the host population appeared to be the main constraint limiting parasite population growth.

Spatial and temporal variation in the infracommunity structure of helminths of Apodemus sylvaticus(Rodentia: Muridae)

Parasitology ◽  
1989 ◽  
Vol 98 (1) ◽  
pp. 145-150 ◽  
Author(s):  
S. S. J. Montgomery ◽  
W. I. Montgomery
Keyword(s):  
Species Richness ◽  
Northern Ireland ◽  
Population Density ◽  
Resource Utilization ◽  
Species Interactions ◽  
Apodemus Sylvaticus ◽  
Host Population ◽  
Spatial And Temporal Variation ◽  
Time And Space ◽  
Animal Material

SummaryMean species richness and diversity of the helminth infracommunity of Apodemus sylvaticus in woodland areas of Co. Down, Northern Ireland, varied in time and space. Variation in infracommunity structure among individual hosts, however, always accounted for more than 60% of the variation in the data from different places or different times. Helminth species richness increased with increasing population density, the percentage of the host population 16 weeks old or older, and the proportion of the host population with animal material in their stomachs, at two sites monitored over 33 months. The basis for spatial variation in infracommunity structure is less certain but host dynamics and differences in diet are likely to play some role. It is concluded that analysis at the infracommunity level focuses closely on the potential for species interactions and overlap in resource utilization. Infracommunity structure, at least in the case of A. sylvaticus, varies markedly in time and space and between individual hosts. Such variation should not be ignored in comparative studies.

Epidemiology of nematode infections of Soay sheep (Ovis aries L.) on St Kilda

Parasitology ◽  
1992 ◽  
Vol 105 (3) ◽  
pp. 481-492 ◽  
Author(s):  
F. M. D. Gulland ◽  
M. Fox
Keyword(s):  
Population Density ◽  
Infection Intensity ◽  
Host Population ◽  
Ovis Aries ◽  
Sheep Population ◽  
Soay Sheep ◽  
Infective Larvae ◽  
Population Crash ◽  
Faecal Egg Counts ◽  
Bad Weather

SUMMARYThe epidemiology of nematode infections of Soay sheep on the island of St Kilda over a period of 2 years (August 1988–August 1990) spanning a host population crash is described. Infective larvae (L3) levels on pasture were high (2422±365 L3/kg D.M. grass in midsummer 1988) when host population density was high, decreasing after the sheep population declined by 70% in early 1989 (601 ±14 L3/kg D.M. in midsummer 1989). The availability of infective larvae to sheep increased during the winter of 1988–1989, probably as a result of concentration of existing larvae on grass as vegetation was destroyed by bad weather and overgrazing. Increased availability of pre-parasitic stages was accompanied by a marked increased in faecal egg counts from sheep of all ages and both sexes. Prevalence and intensity of infection (faecal egg counts) were higher in males than females throughout the 2-year study (χ2 = 208.3, P < 0.005 and F1.2000 = 304, P < 0.001 respectively), except during the lambing periods, and decreased with age in both sexes. Changes in prevalence and intensity of strongyle infections were associated with changes in host population density. Prevalence and intensity of Dictyocaulus filaria larvae in faeces increased during the host population crash. Infection intensity decreased with age (F1.203 = 44.02, P < 0.001) and was higher in males than females (F1.203 = 13.45, P < 0.001).

scholarly journals Disentangling bacterial invasiveness from lethality in an experimental host-pathogen system

2018 ◽  
Author(s):  
Tommaso Biancalani ◽  
Jeff Gore
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Mortality Rate ◽  
Serratia Marcescens ◽  
Salmonella Enterica ◽  
Disease Ecology ◽  
Evolutionary Biology ◽  
Host Population ◽  
Infection Process ◽  
Laboratory Population ◽  
Treatment And Prevention

ABSTRACTQuantifying virulence remains a central problem in human health, pest control, disease ecology, and evolutionary biology. Bacterial virulence is typically quantified by theLT50(i.e.the time taken to kill 50% of infected hosts), however, such an indicator cannot account for the full complexity of the infection process, such as distinguishing between the pathogen’s ability to colonize vs. kill the hosts. Indeed, the pathogen needs to breach the primary defenses in order to colonize, find a suitable environment to replicate, and finally express the virulence factors that cause disease. Here, we show that two virulence attributes, namely pathogen lethality and invasiveness, can be disentangled from the survival curves of a laboratory population ofCaenorhabditis elegansnematodes exposed to three bacterial pathogens:Pseudomonas aeruginosa,Serratia marcescensandSalmonella enterica. We first show that the host population eventually experiences a constant mortality rate, which quantifies the lethality of the pathogen. We then show that the time necessary to reach this constant-mortality rate regime depends on the pathogen growth rate and colonization rate, and thus determines the pathogen invasiveness. Our framework reveals thatSerratia marcescensis particularly good at the initial colonization of the host, whereasSalmonella entericais a poor colonizer yet just as lethal once established.Pseudomonas aeruginosa, on the other hand, is both a good colonizer and highly lethal after becoming established. The ability to quantitatively characterize the ability of different pathogens to perform each of these steps has implications for treatment and prevention of disease and for the evolution and ecology of pathogens.

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