Computer model of the maintenance and selection of genetic heterogeneity in polygamous helminths

Parasitology ◽  
1995 ◽  
Vol 111 (4) ◽  
pp. 531-536 ◽  
Author(s):  
A. Saul
Keyword(s):  
Genetic Drift ◽  
Computer Model ◽  
Genetic Heterogeneity ◽  
Host Selection ◽  
Selection Pressure ◽  
Intestinal Helminths ◽  
Infection Rates ◽  
Stochastic Fluctuations ◽  
Stochastic Simulation Model ◽  
Selection Of

SUMMARYA stochastic simulation model of the transmission and maintenance of genetic heterogeneity in the absence and presence of external selection pressures is presented for polygamous intestinal helminths such as Ascaris. The model assumes that the density distribution of the adult parasites is highly aggregated and that density-dependent effects on fecundity are important. The model gives rise to stable infection rates in the host. Where the parasite population contains genetic heterogeneity, with the exception of stochastic fluctuations which models genetic drift, the ratio of the different alleles remained constant over extended periods of time. This result contrasts with that of an earlier analytical model (Anderson, R. M., May, M. R. & Gutpa S. (1989) Parasitology 99, S59–S79), in which uneven mating probabilities for the different combinations of worm possible in a host was postulated to inevitably lead to fixation of the most abundant allele. New results suggest that in spite of the restricted choice of mating available to a worm in the confines of a host, selection pressure always leads to enrichment of the parasites carrying resistant alleles.

Genetic heterogeneity in helminths — a reply

Parasitology ◽  
1995 ◽  
Vol 111 (4) ◽  
pp. 537-538 ◽  
Author(s):  
R. M. Anderson ◽  
R. M. May ◽  
S. Gupta
Keyword(s):  
Computer Simulation ◽  
Computer Model ◽  
Genetic Heterogeneity ◽  
Rare Allele ◽  
Intestinal Helminths ◽  
Selection Pressures ◽  
Probability Functions ◽  
Selective Pressures ◽  
Selective Effects ◽  
Selection Of

The previous paper in this issue Computer model of the maintenance and selection of genetic heterogeneity in polygamous helminths by Saul uses an individual-based computer simulation to explore aspects of the transmission and maintenance of genetic heterogeneity among polygamous intestinal helminths, both in the absence and in the presence of external selection pressures resulting from chemotherapy. Saul finds that, in the absence of any selective effects, genetic heterogeneity persists, contradicting the results presented by Anderson, May & Gupta (1989) that mating probability functions create density-dependent and frequency-dependent selective pressures against a rare allele, which eventually leads to its elimination.

scholarly journals Stochastic extinction and the selection of the transmission mode in microparasites

2008 ◽  
Vol 5 (26) ◽  
pp. 1031-1039 ◽  
Author(s):  
Narges Bahi-Jaber ◽  
David Fouchet ◽  
Dominique Pontier
Keyword(s):  
Selection Pressure ◽  
Transmission Mode ◽  
Deterministic Models ◽  
Selection Pressures ◽  
Sexually Transmitted ◽  
Stochastic Fluctuations ◽  
Immunodeficiency Virus ◽  
Parasite Evolution ◽  
Stochastic Selection ◽  
Selection Of

Stochastic fluctuations in the transmission process of microparasites generate a risk of parasite extinction that cannot be assessed by deterministic models, especially in host populations of small size. While this risk of extinction represents a strong selection pressure for microparasites, it is usually not clearly separated from the deterministic ones. We suggest here that this stochastic selection pressure can affect the selection of the transmission mode of microparasites. To avoid extinction, parasites should maximize their inter-population transmission to ensure frequent reintroductions. Since the types of contacts may differ if congeners belong to the same or distinct populations, strains that are mainly transmitted through inter-population contacts might be selected. To examine this assumption, we analyse the issue of the competition between two strains differing in their transmission mode using a stochastic metapopulation model in which hosts may display different behaviours inside and outside their populations. We show that stochastic selection pressures may drive parasite evolution towards a transmission mode that maximizes the persistence of the parasite. We study the conditions under which stochastic selection pressures may surpass the deterministic ones. Our results are illustrated by the cases of feline immunodeficiency virus in cats and of sexually transmitted diseases in mammals.

scholarly journals Random-Walk, Agent-Level Pandemic Simulation (RAW-ALPS) for Analyzing Effects of Different Lockdown Measures

2021 ◽  
Vol 7 ◽  
Author(s):  
Anuj Srivastava
Keyword(s):  
Random Walk ◽  
Simulation Model ◽  
Random Walks ◽  
Stochastic Simulation ◽  
Preventive Measures ◽  
Infection Rates ◽  
Physical Proximity ◽  
Stochastic Simulation Model ◽  
Restrictive Measures ◽  
Effective Use

This article develops an agent-level stochastic simulation model, termed RAW-ALPS, for simulating the spread of an epidemic in a community. The mechanism of transmission is agent-to-agent contact, using parameters reported for the COVID-19 pandemic. When unconstrained, the agents follow independent random walks and catch infections due to physical proximity with infected agents. Under lockdown, an infected agent can only infect a coinhabitant, leading to a reduction in the spread. The main goal of the RAW-ALPS simulation is to help quantify the effects of preventive measures—timing and durations of lockdowns—on infections, fatalities, and recoveries. The model helps measure changes in infection rates and casualties due to the imposition and maintenance of restrictive measures. It considers three types of lockdowns: 1) whole population (except the essential workers), 2) only the infected agents, and 3) only the symptomatic agents. The results show that the most effective use of lockdown measures is when all infected agents, including both symptomatic and asymptomatic, are quarantined, while the uninfected agents are allowed to move freely. This result calls for regular and extensive testing of a population to isolate and restrict all infected agents.

Notes on parasites of Pentatomidae and Scutelleridae (Hemiptera-Heteroptera) in Middle East countries, with observations on biological control

1962 ◽  
Vol 53 (2) ◽  
pp. 241-256 ◽  
Author(s):  
E. S. Brown
Keyword(s):  
Biological Control ◽  
Middle East ◽  
Host Selection ◽  
Biological Control Agent ◽  
Control Agent ◽  
Sunn Pest ◽  
Eurygaster Integriceps ◽  
Middle East Countries ◽  
Central Turkey ◽  
Selection Of

A number of observations were made on parasites of certain Pentatomoids (sunn pest) attacking wheat in Middle East countries, during the course of other work on these pests. The principal host species studied were Eurygaster integriceps Put., E. maura (L.) and Aelia rostrata Boh. The data concern both Dipterous (Tachinid) endoparasites of the adult bugs, and also Hymenopterous (Scelionid) egg-parasites; the observations were made principally in central Turkey, and in the Varamine district of Iran. A few observations on predators were made also.The data concerning Tachinids consist of host records for six species of parasites. In no case observed by the author did these parasites appear to be of great importance in reducing the numbers of sunn pest; the same is true of the few instances of predators recorded.Observations were made on six species of Scelionid egg-parasites (five species of Asolcus and one of Hadronotus), five of which were bred from eggs of four species of Pentatomoid hosts collected in the field. The species concerning which the most comprehensive data were obtained were Asolcus rufiventris (Mayr), A. semistriatus (Nees) and A. vassilievi (Mayr). Egg-parasites are well known to be more efficacious in reducing sunn-pest populations, and A. semistriatus has been extensively used in Iran as a biological control agent. The data obtained enabled some ideas which are of importance for the use of egg-parasites in biological control to be formed and discussed. These concern principally (a) the susceptibilities of different hosts to parasitisation; (b) host selection by parasites; (c) the selection of a species of parasite most suitable for biological control in a particular area.

scholarly journals The Carnivore Connection Hypothesis: Revisited

2012 ◽  
Vol 2012 ◽  
pp. 1-9 ◽  
Author(s):  
Jennie C. Brand-Miller ◽  
Hayley J. Griffin ◽  
Stephen Colagiuri
Keyword(s):  
Insulin Resistance ◽  
Type 2 Diabetes ◽  
Selection Pressure ◽  
Glycemic Load ◽  
Dietary Carbohydrate ◽  
Recent Exposure ◽  
Agricultural Revolution ◽  
High Prevalence ◽  
Selection Of

The “Carnivore Connection” hypothesizes that, during human evolution, a scarcity of dietary carbohydrate in diets with low plant : animal subsistence ratios led to insulin resistance providing a survival and reproductive advantage with selection of genes for insulin resistance. The selection pressure was relaxed at the beginning of the Agricultural Revolution when large quantities of cereals first entered human diets. The “Carnivore Connection” explains the high prevalence of intrinsic insulin resistance and type 2 diabetes in populations that transition rapidly from traditional diets with a low-glycemic load, to high-carbohydrate, high-glycemic index diets that characterize modern diets. Selection pressure has been relaxed longest in European populations, explaining a lower prevalence of insulin resistance and type 2 diabetes, despite recent exposure to famine and food scarcity. Increasing obesity and habitual consumption of high-glycemic-load diets worsens insulin resistance and increases the risk of type 2 diabetes in all populations.

scholarly journals Exploring Plasmodium falciparum Var Gene Expression to Assess Host Selection Pressure on Parasites During Infancy

2019 ◽  
Vol 10 ◽  
Author(s):  
Cheryl A. Kivisi ◽  
Michelle Muthui ◽  
Martin Hunt ◽  
Greg Fegan ◽  
Thomas Dan Otto ◽  
...  
Keyword(s):  
Gene Expression ◽  
Plasmodium Falciparum ◽  
Host Selection ◽  
Selection Pressure ◽  
Var Gene
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