Population dynamics of snail infection by miracidia

Parasitology ◽  
1978 ◽  
Vol 77 (2) ◽  
pp. 201-224 ◽  
Author(s):  
R. M. Anderson
Keyword(s):  
Empirical Evidence ◽  
Rate Of Change ◽  
Infection Rates ◽  
Snail Infection ◽  
Demographic Stochasticity ◽  
Susceptibility To Infection ◽  
Biological Features ◽  
Age Dependent ◽  
Theoretical Predictions ◽  
Over Dispersion

SummaryThe essential biological features of snail infection by miracidia are incorporated into a simple model which describes the rate of change with respect to time of the number of miracidial infections/host. The model is based on the assumption that the net rate of infection is directly proportional to the density of both miracidia and hosts. Empirical evidence is provided to support this assumption. The basic framework of the model is expanded to take into account demographic stochasticity in infection and is used to predict the percentage of snails that become infected after exposure to a known number of miracidia for a set period of time. The influence of miracidial mortalities and age-dependent infectivity are examined and theoretical predictions are compared with a range of experimental results.Underlying heterogeneity in the distribution of the number of infections/snail is shown to generate an artifactual decrease in infection rates as exposure density rises, if rate estimation procedures are based on an assumption of randomness. Empirical evidence is presented to illustrate the generation of over-dispersion in the number of miracidial infections/snail under tightly controlled laboratory conditions, using supposedly homogeneous snail populations.Biological causes for underlying patterns of heterogeneity are discussed in relation to snail susceptibility to infection and ‘attractiveness’ to infective stages.

Transmission ofSchistosoma mansonifrom man to snail: experimental studies of miracidial survival and infectivity in relation to larval age, water temperature, host size and host age

Parasitology ◽  
1982 ◽  
Vol 85 (2) ◽  
pp. 339-360 ◽  
Author(s):  
R. M. Anderson ◽  
J. G. Mercer ◽  
R. A. Wilson ◽  
N. P. Carter
Keyword(s):  
Experimental Studies ◽  
Larval Survival ◽  
Host Size ◽  
Host Age ◽  
Infection Rates ◽  
Susceptibility To Infection ◽  
Size Dependent ◽  
Age Dependent ◽  
Influence Of Temperature On ◽  
The Relationship

SUMMARYWe report the results of experimental work on (a) the influence of temperature on the age-dependent survival and infectivity of the mira-cidia ofSchistosoma mansoniand (b) the relationship between snail age, snail size and susceptibility to infection. The death rate of miracidia declined exponentially with age where life-expectancy was maximal (approximately 16 h) at 15 °C. Infectivity also declined rapidly with larval age but, in contrast to larval survival, the rate of infection was at a maximum at 25 °C. Snail susceptibility was shown to be more closely correlated with host size rather than host age. Susceptibility declined exponentially with increased host size. Size-dependent susceptibility was shown to generate concave age-prevalence curves for infection within snail populations, where the maximum prevalence is generated in snails of intermediary age. Simple mathematical models are developed to aid estimation of larval survival and infection rates and experimental results are discussed in relation to the overall transmission success of the parasite from man to snail.

scholarly journals Behaviour of albino and melanic variants of Biomphalaria glabrata Say, 1818 (Mollusca: Planorbidae) following infection by Schistosoma mansoni Sambon, 1907

2009 ◽  
Vol 69 (1) ◽  
pp. 217-222 ◽  
Author(s):  
SM. Allegretti ◽  
JF. Carvalho ◽  
LA. Magalhães ◽  
EM. Zanotti-Magalhães
Keyword(s):  
Mortality Rate ◽  
Schistosoma Mansoni ◽  
Cross Sections ◽  
Biomphalaria Glabrata ◽  
Infection Rates ◽  
Susceptibility To Infection ◽  
Belo Horizonte

The behaviour of the albino and melanic variants of Biomphalaria glabrata of Belo Horizonte (MG. Brazil) was studied comparatively, in terms of their respective susceptibilities to infection by Schistosoma mansoni of the same origin, through observation of the elimination of cercariae for a three-month period and the calculation of mortality and infection rates, in control and in infected snails. The number of amoebocytes, granulocytes and hyalinocytes in the circulating hemolymph during different periods of infection was analyzed. The evolution of the infection in the tissues was observed by means of histological cross-sections. The melanic variant showed greater susceptibility to infection and a higher mortality rate. The albino variant showed a higher number of circulating amoebocytes, both granulocytes and hyalinocytes. A higher number of degenerated sporocysts were seen in the histological cross-sections of the albino variant. The results suggest that the melanic variant of B. glabrata was more susceptible to infection by S. mansoni than was the albino variant.

scholarly journals Diversity–disturbance relationships: frequency and intensity interact

2012 ◽  
Vol 8 (5) ◽  
pp. 768-771 ◽  
Author(s):  
Alex R. Hall ◽  
Adam D. Miller ◽  
Helen C. Leggett ◽  
Stephen H. Roxburgh ◽  
Angus Buckling ◽  
...  
Keyword(s):  
Species Diversity ◽  
Empirical Evidence ◽  
Empirical Studies ◽  
Ecological Theory ◽  
Intermediate Disturbance Hypothesis ◽  
Intermediate Disturbance ◽  
Disturbance Frequency ◽  
Theoretical Predictions ◽  
Experimental Populations ◽  
Disturbance Hypothesis

An influential ecological theory, the intermediate disturbance hypothesis (IDH), predicts that intermediate levels of disturbance will maximize species diversity. Empirical studies, however, have described a wide variety of diversity–disturbance relationships (DDRs). Using experimental populations of microbes, we show that the form of the DDR depends on an interaction between disturbance frequency and intensity. We find that diversity shows a monotonically increasing, unimodal or flat relationship with disturbance, depending on the values of the disturbance aspects considered. These results confirm recent theoretical predictions, and potentially reconcile the conflicting body of empirical evidence on DDRs.

Investigating over-dispersion; Moniliformis (Acanthocephala) and rats

Parasitology ◽  
1984 ◽  
Vol 88 (2) ◽  
pp. 317-331 ◽  
Author(s):  
D. W. T. Cromptom ◽  
A. E. Keymer ◽  
S. E. Arnold
Keyword(s):  
Experimental Investigation ◽  
Male And Female ◽  
Parasite Survival ◽  
Tentative Hypothesis ◽  
Age Dependent ◽  
Outbred Strain ◽  
Ad Libitum ◽  
Over Dispersion ◽  
Age And Sex ◽  
Host Heterogeneity

SUMMARYAn analysis of the frequency distribution of numbers of Moniliformis dubius in rats of an outbred strain of Wistar origin (CFHB) and feeding ad libitum on Oxoid 41B diet, showed that over-dispersion occurred regardless of the age and sex of the rats and the infective dose given (12, 20 or 40 cystacanths/rat). Over-dispersion was also shown to be independent of variability in the age and sex of the cystacanths given. The analysis demonstrated that the over-dispersion declined as the course of the infection proceeded. As expected, parasite survival was found to be age-dependent with female worms living longer, on average, than males, and both male and female worms living longer in rats given 12 as opposed to 20 cystacanths. Possible mechanisms for generating the over-dispersion observed during this work are discussed and a tentative hypothesis, invoking host heterogeneity with regard to carbohydrate availability in the small intestine, is proposed for further experimental investigation.

The role of spore morphology in horizontal transmission of a microsporidium of Daphnia

Parasitology ◽  
2018 ◽  
Vol 145 (11) ◽  
pp. 1452-1457 ◽  
Author(s):  
Hadas Urca ◽  
Frida Ben-Ami
Keyword(s):  
Daphnia Magna ◽  
Horizontal Transmission ◽  
Spore Morphology ◽  
Infection Rates ◽  
Microsporidian Parasite ◽  
Parasite Isolate ◽  
Theoretical Predictions ◽  
Host Mortality ◽  
Host Clone

AbstractThe microsporidian parasite Hamiltosporidium tvaerminnensis can infect Daphnia magna both horizontally (through environmental spores) and vertically (through parthenogenetic and sexually produced eggs). The spores of H. tvaerminnensis come in three distinguishable morphologies, which are thought to have different roles in the transmission of the parasite. In this study, we examined the role of the two most common spore morphologies (i.e. oval-shaped spores and pear-shaped spores) in horizontal transmission of H. tvaerminnensis. To this end, we infected hosts with solutions consisting of either mostly oval- or mostly pear-shaped spores, and quantified infection rates, parasite-induced host mortality and mean number of parasite spores produced per host. We found that spore morphology by itself did not influence infection rates and parasite-induced host mortality. Instead, host clone and parasite isolate interacted with spore morphology in shaping infection outcome and mortality. Thus, there appear to be strong genotype-by-genotype (G × G) interactions in this system. While there is no dispute that H. tvaerminnensis can transmit both vertically and horizontally, our findings do not support theoretical predictions that different spore morphologies hold different roles in horizontal transmission of H. tvaerminnensis.

Age-related effects of digoxin on myocardial contractility and Na-K pump in sheep

1982 ◽  
Vol 243 (4) ◽  
pp. H517-H522
Author(s):  
T. J. Hougen ◽  
W. F. Friedman
Keyword(s):  
Active Transport ◽  
Monovalent Cation ◽  
Left Ventricular ◽  
Rate Of Change ◽  
Control Group ◽  
Base Line ◽  
Experimental Conditions ◽  
Adult Sheep ◽  
Age Related ◽  
Age Dependent

The age-dependent effects of an acute nontoxic, positively inotropic dose of digoxin on myocardial monovalent cation active transport were determined in fetal, newborn, and adult sheep. Thirty-five lightly sedated, closed-chest animals were instrumented to record electrocardiogram, left ventricular (LV) pressure, and rate of change of LV pressure (LV dP/dt). Ouabain-inhibitable uptake of Rb+ (86Rb+) was measured in both right ventricular (RV) and LV slices from control animals and in animals infused with [3H]digoxin (0.04 mg/kg) sufficient to cause an increase in LV dP/dt without toxicity. Sixty minutes after digoxin, LV dP/dt increased 123% over base-line values in fetuses, 131% in newborns, and 165% in adult animals. RV and LV myocardial digoxin concentrations were similar in all groups. Rb+ active transport was significantly reduced in both RV and LV tissue from all animals 60 min after digoxin. Control animals showed no significant changes in contractility or Rb+ active transport among the control group of fetal, newborn, or adult sheep. Acute infusions of digoxin increased LV contractility in each age group and was accompanied by digoxin-induced inhibition of myocardial Rb+ active transport. No age-related differences in the extent of Rb+ active transport among control or among digoxin-treated animals were observed under these experimental conditions. These studies suggest that the differential response to the therapeutic and toxic effects of digoxin in sheep of various ages does not reside in an age-dependent response of the myocardial sodium pump to digoxin.

The Engine or the Caboose? Resource Industries and Twentieth-Century Canadian Economic Performance

2007 ◽  
Vol 67 (1) ◽  
pp. 1-32 ◽  
Author(s):  
Ian Keay
Keyword(s):  
Twentieth Century ◽  
Empirical Evidence ◽  
Natural Resource ◽  
Economic Performance ◽  
Positive Impact ◽  
Rate Of Change ◽  
Domestic Economy ◽  
Intensive Production ◽  
Resource Endowment ◽  
Per Capita

The Canadian economy, already wealthy, diverse, and relatively industrial at the dawn of the twentieth century, had not yet outgrown its reliance on resource-intensive production. Empirical evidence indicates that the exploitation of Canada's natural resource endowment made direct and indirect contributions to the size and efficiency of the twentieth-century domestic economy. I conclude that the concentration of capital and labor in resource industries did not constrain the rate of change of Canadian real GNP per capita between 1900 and 1999, and it appears to have had a substantial positive impact on the level of real GNP per capita.

On the interpretation of age—prevalence curves for schistosome infections of host snails

Parasitology ◽  
1989 ◽  
Vol 99 (1) ◽  
pp. 47-56 ◽  
Author(s):  
M. E. J. Woolhouse
Keyword(s):  
Survival Rate ◽  
Field Studies ◽  
Significant Loss ◽  
High Rate ◽  
Snail Population ◽  
Infection Rates ◽  
Force Of Infection ◽  
Age Dependent ◽  
The Relationship ◽  
Patent Infection

SUMMARYThe prevalence of schistosome infections in intermediate host snails varies with snail age. The relationship between age and prevalence, the age—prevalence curve, is complex and may vary in space and time, and among parasite—host species. Field studies show that the shape of the age—prevalence curve may be seasonally variable, and that at some times there may be a decline in prevalence among older snails. This paper attempts to explain these observations in terms of the underlying epidemiological processes. A discrete-time version of Muench's catalytic model for age-dependent infection is developed. Model simulations were carried out using life-history and epidemiological parameters derived from studies ofSchistosoma haematobium—Bulinus globususin Zimbabwe. Analysis of model behaviour identifies aspects of the schistosome— snail interaction that affect the shape of the age—prevalence curve. The following features can result in a decline in prevalence among older snails. (1) A decrease in the survival rate of patent infected snails with age. (2) A decrease in the force of infection with age. (3) A high rate of loss of infection. (4) A heterogeneity in the snail population such that the probability of infection is correlated with snail fecundity. (This would occur if there existed a spatial correlation between force of infection and fecundity, or if there were a correlation between fecundity and susceptibility.) The evidence for the occurrence of these features in the field is assessed. Survival rate is related more closely to the duration of patent infection than to ageper se. The evidence for age-dependent force of infection is equivocal. Significant loss-of-infection rates have yet to be demonstrated. Heterogeneities in force of infection and fecundity have been reported and, for the Zimbabwe data, this mechanism can explain seasonally in the age—prevalence curve as a function of known seasonal variation in the force of infection and snail fecundity.

Distribution of schistosome genetic diversity within naturally infected Rattus rattus detected by RAPD markers

Parasitology ◽  
1996 ◽  
Vol 113 (6) ◽  
pp. 511-517 ◽  
Author(s):  
V. Barral ◽  
S. Morand ◽  
J. P. Pointier ◽  
A. Théron
Keyword(s):  
Genetic Diversity ◽  
Rapd Markers ◽  
Random Amplified Polymorphic Dna ◽  
Rattus Rattus ◽  
High Mobility ◽  
Genotypic Diversity ◽  
Vertebrate Host ◽  
Infection Rates ◽  
Snail Infection ◽  
Vertebrate Hosts

SUMMARYRandom amplified polymorphic DNA markers (RAPD) were used to visualize the genetic diversity within and between infrapopulations of Schistosoma mansoni recovered from the natural vertebrate host, Rattus rattus, trapped at an insular Guadeloupean focus. Phenotypes were characterized by the sex of the parasites and by 8 polymorphic markers generated by 3 primers. Among the 212 parasite individuals recovered from 10 infected rats, 78 genotypes were characterized. All the hosts naturally infected harboured multiple parasite genotypes with a maximum diversity of 28 genotypes/host. Phenotypic and genotypic diversity calculated by Shannon-Wiener's indices and Lynch and Milligan's estimators respectively is, on average, greater within than between hosts. Considering the very low snail infection rates observed in this focus and the rapid turnover of the vertebrate hosts, our results suggest that the high mobility of the vertebrate host and/or plurimiracidial snail infections could be factors responsible for parasite genetic diversity within hosts.

Dynamics of gastropod infection by first-stage larvae of protostrongylid nematodes — a model

Parasitology ◽  
1993 ◽  
Vol 107 (5) ◽  
pp. 537-544 ◽  
Author(s):  
P. Řezáč ◽  
P. Kindlmann ◽  
I. Dostálková ◽  
E. Holasová
Keyword(s):  
Experimental Design ◽  
Infective Larva ◽  
Snail Infection ◽  
Instantaneous Rate ◽  
Rate Of Penetration ◽  
Susceptibility To Infection ◽  
Species Specific ◽  
Design Factors ◽  
Best Fit ◽  
Penetration Probability

SUMMARYFor the description of the dynamics of snail infection by the 1st-stage larvae of protostrongylid nematodes, Skorping (1988) used the miracidia-snail model (Anderson, 1978). Here it is shown that, in contrast to miracidia, in protostrongylids the instantaneous rate of infection, α, is strongly dependent on the experimental design (factors like host size and size of the experimental arena). With respect to this, Anderson's model is modified by incorporation of the experimental design. The parameter α in its new sense as the rate of penetration (probability that the infective larva will penetrate into the host during a time unit) is shown to remain dependent, although much less so, on the experimental design. Only the inclusion of the assumed effect of mucus, which decreases the rate of penetration, yields a parameter α0 (the initial rate of penetration), which is completely independent of the design of the experiment, is species-specific, and also gives the best fit to the empirical data. As the above-mentioned factors can strongly influence the value of the instantaneous rate of infection in the laboratory experiments, α0 is more suitable as a measure of either the larval infectivity for the snail or snail susceptibility to infection by the protostrongylid larvae.

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