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.

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.

Larval survival characteristics and behaviour of the gill monogenean Discocotyle sagittata

Parasitology ◽  
1998 ◽  
Vol 117 (5) ◽  
pp. 491-498 ◽  
Author(s):  
A. M. GANNICOTT ◽  
R. C. TINSLEY
Keyword(s):  
Survival Time ◽  
Seasonal Changes ◽  
Larval Survival ◽  
Parasite Transmission ◽  
Laboratory Studies ◽  
Temperature Dependent ◽  
Maximum Life Span ◽  
Age Dependent ◽  
Increasing Temperature ◽  
The Relationship

The survival characteristics of Discocotyle sagittata larvae are both age- and temperature-dependent. In laboratory studies at constant temperatures of 6, 10, 13, 18 and 22°C, oncomiracidia had a maximum life-span of 96 h at 6°C, declining with increasing temperature to 26 h at 22°C. Larval swimming activity was also age dependent, and continued for a large proportion of survival time. The relationship between time at which larvae stop swimming as a proportion of total survival time was statistically significant between temperatures. Proportionally, oncomiracidia swam for longer periods at lower temperatures. As oncomiracidia age, they become progressively less active, spending less time in the water column. In contrast to observations recorded in the literature, D. sagittata larvae are infective soon after emergence (within the minimum of 2 h studied), and feed on blood from the gill capillaries within 2 h post-exposure. The temperature-dependent characteristics of the larval stage are likely to have important implications for seasonal changes in parasite transmission.

Experimental studies on the transmission dynamics of the cercariae of Echinoparyphium recurvatum (Digenea: Echinostomatidae)

Parasitology ◽  
1983 ◽  
Vol 87 (1) ◽  
pp. 167-174 ◽  
Author(s):  
N. A. Evans ◽  
D. M. Gordon
Keyword(s):  
Life Span ◽  
Intermediate Host ◽  
Experimental Studies ◽  
Intermediate Hosts ◽  
Maximum Life Span ◽  
Age Dependent ◽  
Second Intermediate Host ◽  
The Mean ◽  
The Relationship ◽  
First Intermediate Host

SUMMARYAge-dependent survival and infectivity characteristics are described for the cercariae of Echinoparyphium recurvatum. At 18 °C the maximum life-span of the cercariae was 48 h and 50% survival occurred at 30·5 h. Infectivity of cercariae to the second intermediate host, Lymnaea peregra was maximal approximately 2 h after emission from the first intermediate host and it subsequently declined to zero at 19 h. It is suggested that the period of sub-maximal infectivity at the beginning of the cercarial life-span may represent a phase during which dispersal is an important function of the larvae. The relationship between infective stage density and establishment success was linear up to densities equivalent to 5000 cercariae/1. At higher cercarial densities the proportion of parasites establishing in second intermediate hosts declined progressively with increasing cercarial density. The mean number of parasites establishing/host increased linearly with increasing host size.

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.

Potential Role of Inflammation in Associations between Particulate Matter and Heart Failure

2018 ◽  
Vol 24 (3) ◽  
pp. 341-358 ◽  
Author(s):  
Xiaotong Ji ◽  
Yingying Zhang ◽  
Guangke Li ◽  
Nan Sang
Keyword(s):  
Heart Failure ◽  
Particulate Matter ◽  
Inflammatory Response ◽  
Heart Diseases ◽  
Experimental Studies ◽  
Epidemiological Studies ◽  
Inflammatory Mechanism ◽  
High Concentrations ◽  
Future Work ◽  
The Relationship

Recently, numerous studies have found that particulate matter (PM) exposure is correlated with increased hospitalization and mortality from heart failure (HF). In addition to problems with circulation, HF patients often display high expression of cytokines in the failing heart. Thus, as a recurring heart problem, HF is thought to be a disorder characterized in part by the inflammatory response. In this review, we intend to discuss the relationship between PM exposure and HF that is based on inflammatory mechanism and to provide a comprehensive, updated evaluation of the related studies. Epidemiological studies on PM-induced heart diseases are focused on high concentrations of PM, high pollutant load exposure in winter, or susceptible groups with heart diseases, etc. Furthermore, it appears that the relationship between fine or ultrafine PM and HF is stronger than that between HF and coarse PM. However, fewer studies paid attention to PM components. As for experimental studies, it is worth noting that coarse PM may indirectly promote the inflammatory response in the heart through systematic circulation of cytokines produced primarily in the lungs, while ultrafine PM and its components can enter circulation and further induce inflammation directly in the heart. In terms of PM exposure and enhanced inflammation during the pathogenesis of HF, this article reviews the following mechanisms: hemodynamics, oxidative stress, Toll-like receptors (TLRs) and epigenetic regulation. However, many problems are still unsolved, and future work will be needed to clarify the complex biologic mechanisms and to identify the specific components of PM responsible for adverse effects on heart health.

scholarly journals Experimental studies on the transformation from firn to ice in the wet-snow zone of temperate glaciers

1997 ◽  
Vol 24 ◽  
pp. 181-185 ◽  
Author(s):  
Katsuhisa Kawashima ◽  
Tomomi Yamada
Keyword(s):  
Experimental Studies ◽  
Ice Formation ◽  
Compression Tests ◽  
Densification Rate ◽  
Overburden Pressure ◽  
Proportionality Constant ◽  
Wet Snow ◽  
Water Saturated ◽  
The Relationship ◽  
Good Agreement

The densification of water-saturated firn, which had formed just above the firn-ice transition in the wet-snow zone of temperate glaciers, was investigated by compression tests under pressures ranging from 0.036 to 0.173 MPa, with special reference to the relationship between densification rate, time and pressure. At each test, the logarithm of the densification rate was proportional to the logarithm of the time, and its proportionality constant increased exponentially with increasing pressure. The time necessary for ice formation in the firn aquifer was calculated using the empirical formula obtained from the tests. Consequently, the necessary time decreased exponentially as the pressure increased, which shows that the transformation from firn in ice can be completed within the period when the firn aquifer exists, if the overburden pressure acting on the water-saturated firn is above 0.12–0.14 MPa. This critical value of pressure was in good agreement with the overburden pressure obtained from depth–density curves of temperate glaciers. It was concluded that the depth of firn–ice transition was self-balanced by the overburden pressure to result in the concentration between 20 and 30 m.

scholarly journals Application of intelligent orienteering based on Internet of things

2020 ◽  
Vol 2020 (1) ◽  
Author(s):  
Donghui Zhang ◽  
Ruijie Liu
Keyword(s):  
Internet Of Things ◽  
Network Architecture ◽  
Emergency Services ◽  
Simulation Experiment ◽  
Experimental Studies ◽  
Signal Stability ◽  
Anchor Nodes ◽  
Set Up ◽  
The Relationship ◽  
The Internet Of Things

Abstract Orienteering has gradually changed from a professional sport to a civilian sport. Especially in recent years, orienteering has been widely popularized. Many colleges and universities in China have also set up this course. With the improvement of people’s living conditions, orienteering has really become a leisure sport in modern people’s life. The reduced difficulty of sports enables more people to participate, but it also exposes a series of problems. As the existing positioning technology is relatively backward, the progress in personnel tracking, emergency services, and other aspects is slow. To solve these problems, a new intelligent orienteering application system is developed based on the Internet of things. ZigBee network architecture is adopted in the system. ZigBee is the mainstream scheme in the current wireless sensor network technology, which has many advantages such as convenient carrying, low power consumption, and signal stability. Due to the complex communication environment in mobile signal, the collected information is processed by signal amplification and signal anti-interference technology. By adding anti-interference devices, video isolators and other devices, the signal is guaranteed to the maximum extent. In order to verify the actual effect of this system, through a number of experimental studies including the relationship between error and traffic radius and the relationship between coverage and the number of anchor nodes, the data shows that the scheme studied in this paper has a greater improvement in comprehensive performance than the traditional scheme, significantly improving the accuracy and coverage. Especially the coverage is close to 100% in the simulation experiment. This research has achieved good results and can be widely used in orienteering training and competition.

External Ventricular Drain Infection

2007 ◽  
Vol 107 (1) ◽  
pp. 248 ◽  
Author(s):  
George K. C. Wong ◽  
Wayne W. S. Poon
Keyword(s):  
Major Trauma ◽  
Independent Predictor ◽  
External Ventricular Drain ◽  
Significant Risk ◽  
Significant Risk Factor ◽  
External Ventricular Drainage ◽  
Infection Rates ◽  
The Mean ◽  
The Relationship ◽  
Shed Light

Object The authors explored the relationship among the duration of external ventricular drainage, revision of external ventricular drains (EVDs), and cerebrospinal fluid (CSF) infection to shed light on the practice of electively revising these drains. Methods In a retrospective study of 199 patients with 269 EVDs in the intensive care unit at a major trauma center in Australasia, the authors found 21 CSF infections. Acinetobacter accounted for 10 (48%) of these infections. Whereas the duration of drainage was not an independent predictor of infection, multiple insertions of EVDs was a significant risk factor. Second and third EVDs in previously uninfected patients were more likely to become infected than first EVDs. An EVD infection was initially identified a mean of 5.5 ±0.7 days postinsertion (standard error of the mean); these data—that is, the number of days—were normally distributed. Conclusions This pattern of infection is best explained by EVD-associated CSF infections being acquired by the introduction of bacteria on insertion of the drain rather than by subsequent retrograde colonization. Elective EVD revision would be expected to increase infection rates in light of these results, and thus the practice has been abandoned by the authors' institution.

Relation between understanding and agreeing in response to one-sentence assertion*

2014 ◽  
Vol 7 (1) ◽  
pp. 36-67 ◽  
Author(s):  
YASUHIRO OZURU ◽  
DAVID BOWIE ◽  
GIULIA KAUFMAN
Keyword(s):  
Cognitive Processes ◽  
Experimental Studies ◽  
Cognitive Response ◽  
Response Options ◽  
Evaluative Response ◽  
Quasi Experimental ◽  
The Relationship

abstractThree quasi-experimental studies were conducted to investigate the relationship between the evaluative (i.e., agree/true) and the meta-cognitive (i.e., understand) response, and to determine which type of response people are more likely to provide when responding to one-sentence assertive statements. In Studies 1 and 2, participants performed two separate tasks in which they were asked to indicate the levels of: (i) understanding and (ii) agreement / perceived truthfulness of 126 one-sentence statements. The results indicated that participants were likely to provide a negative evaluative response (i.e., disagree/false) to a statement that they did not understand. In Study 3, participants were asked to evaluate the same 126 statements and choose between four response options: agree, disagree, understand, do not understand. The results indicated that people are more likely provide an evaluative response regardless of the understandability of a statement. The results of these studies are discussed in relation to (i) pragmatic perspective of how people infer speakers’ meaning, and (ii) cognitive processes underlying evaluative and meta-cognitive response.

scholarly journals 694 Insufficient sleep linked with higher COVID-19 infection cases and deaths in the United States

SLEEP ◽  
2021 ◽  
Vol 44 (Supplement_2) ◽  
pp. A271-A271
Author(s):  
Azizi Seixas ◽  
Nicholas Pantaleo ◽  
Samrachana Adhikari ◽  
Michael Grandner ◽  
Giardin Jean-Louis
Keyword(s):  
Regression Models ◽  
Negative Binomial ◽  
The United States ◽  
Poor Sleep ◽  
County Level ◽  
Infection Rates ◽  
Insufficient Sleep ◽  
Death Rates ◽  
Rural Counties ◽  
The Relationship

Abstract Introduction Causes of COVID-19 burden in urban, suburban, and rural counties are unclear, as early studies provide mixed results implicating high prevalence of pre-existing health risks and chronic diseases. However, poor sleep health that has been linked to infection-based pandemics may provide additional insight for place-based burden. To address this gap, we investigated the relationship between habitual insufficient sleep (sleep <7 hrs./24 hr. period) and COVID-19 cases and deaths across urban, suburban, and rural counties in the US. Methods County-level variables were obtained from the 2014–2018 American community survey five-year estimates and the Center for Disease Control and Prevention. These included percent with insufficient sleep, percent uninsured, percent obese, and social vulnerability index. County level COVID-19 infection and death data through September 12, 2020 were obtained from USA Facts. Cumulative COVID-19 infections and deaths for urban (n=68), suburban (n=740), and rural (n=2331) counties were modeled using separate negative binomial mixed effects regression models with logarithmic link and random state-level intercepts. Zero-inflated models were considered for deaths among suburban and rural counties to account for excess zeros. Results Multivariate regression models indicated positive associations between cumulative COVID-19 infection rates and insufficient sleep in urban, suburban and rural counties. The incidence rate ratio (IRR) for urban counties was 1.03 (95% CI: 1.01 – 1.05), 1.04 (95% CI: 1.02 – 1.05) for suburban, and 1.02 (95% CI: 1.00 – 1.03) rural counties.. Similar positive associations were observed with county-level COVID-19 death rates, IRR = 1.11 (95% CI: 1.07 – 1.16) for urban counties, IRR = 1.04 (95% CI: 1.01 – 1.06) for suburban counties, and IRR = 1.03 (95% CI: 1.01 – 1.05) for rural counties. Level of urbanicity moderated the association between insufficient sleep and COVID deaths, but not for the association between insufficient sleep and COVID infection rates. Conclusion Insufficient sleep was associated with COVID-19 infection cases and mortality rates in urban, suburban and rural counties. Level of urbanicity only moderated the relationship between insufficient sleep and COVID death rates. Future studies should investigate individual-level analysis to understand the role of sleep mitigating COVID-19 infection and death rates. Support (if any) NIH (K07AG052685, R01MD007716, R01HL142066, K01HL135452, R01HL152453

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