bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of measurements of stopping powers of formvar, polyimide, polysulfone, and vyns for 3.6 to 10.5 MeV 7Li ions
Authors: Porter L. E. , Räisänen J. , Munnik F.
Published: November 2002

The stopping powers of formvar, polysulfone, polyimide, and vyns for 7Li projectiles have been measured with the transmission technique and thin foil targets. The experimental data have been analyzed in terms of modified Bethe–Bloch theory to extract characteristic values of the mean excitation energy and Barkas effect parameter, as well as to study the effects of including a single effective charge parameter. Results of this investigation are in general supportive of the outcomes of earlier similar studies with protons and α‐particles traversing the same target materials in the sense that previously reported trends in projectile‐dependent behavior of values of mean excitation energy and Barkas effect parameter are followed in most cases. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Quantum random walks on the set of contingency tables
Authors: Sawae Ryuichi , Sakata Toshio , Takarabe Kenichi , Tei Minaru , Mizuno Youichi , Mori Yoshiyuki , Manmoto Yoshinori
Published: November 2002

In this article, we define the quantum version of this classic Metropolis walks on the set of contingency tables and get several theoretical conclusions with computer simulation for two‐way contingency tables with fixed‐row sums and column sums. Also, quantum random walks for three‐way contingency tables will be defined. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
Comparing proportional hazards and accelerated failure time models for survival analysis
Authors: Orbe Jesus , Ferreira Eva , Núñez‐Antón Vicente
Published: October 2002

This paper describes a method proposed for a censored linear regression model that can be used in the context of survival analysis. The method has the important characteristic of allowing estimation and inference without knowing the distribution of the duration variable. Moreover, it does not need the assumption of proportional hazards. Therefore, it can be an interesting alternative to the Cox proportional hazards models when this assumption does not hold. In addition, implementation and interpretation of the results is simple. In order to analyse the performance of this methodology, we apply it to two real examples and we carry out a simulation study. We present its results together with those obtained with the traditional Cox model and AFT parametric models. The new proposal seems to lead to more precise results. Copyright © 2002 John Wiley & Sons, Ltd.
Assessing intrarater, interrater and test–retest reliability of continuous measurements
Authors: Rousson Valentin , Gasser Theo , Seifert Burkhardt
Published: October 2002

In this paper we review the problem of defining and estimating intrarater, interrater and test–retest reliability of continuous measurements. We argue that the usual notion of product‐moment correlation is well adapted in a test–retest situation, whereas the concept of intraclass correlation should be used for intrarater and interrater reliability. The key difference between these two approaches is the treatment of systematic error, which is often due to a learning effect for test–retest data. We also consider the reliability of a sum and a difference of variables and illustrate the effects on components. Further, we compare these approaches of reliability with the concept of limits of agreement proposed by Bland and Altman (for evaluating the agreement between two methods of clinical measurements) and show how product‐moment correlation is related to it. We then propose new kinds of limits of agreement which are related to intraclass correlation. A test battery to study the development of neuro‐motor functions in children and adolescents illustrates our purpose throughout the paper. Copyright 2002 John Wiley & Sons, Ltd.
Block principal component analysis with application to gene microarray data classification
Authors: Liu Aiyi , Zhang Ying , Gehan Edmund , Clarke Robert
Published: October 2002

We propose a block principal component analysis method for extracting information from a database with a large number of variables and a relatively small number of subjects, such as a microarray gene expression database. This new procedure has the advantage of computational simplicity, and theory and numerical results demonstrate it to be as efficient as the ordinary principal component analysis when used for dimension reduction, variable selection and data visualization and classification. The method is illustrated with the well‐known National Cancer Institute database of 60 human cancer cell lines data (NCI60) of gene microarray expressions, in the context of classification of cancer cell lines. Copyright © 2002 John Wiley & Sons, Ltd.
Binary partitioning for continuous longitudinal data: categorizing a prognostic variable
Authors: Abdolell M. , LeBlanc M. , Stephens D. , Harrison R. V.
Published: October 2002

We investigate a binary partitioning algorithm in the case of a continuous repeated measures outcome. The procedure is based on the use of the likelihood ratio statistic to evaluate the performance of individual splits. The procedure partitions a set of longitudinal data into two mutually exclusive groups based on an optimal split of a continuous prognostic variable. A permutation test is used to assess the level of significance associated with the optimal split, and a bootstrap confidence interval is obtained for the optimal split. Copyright © 2002 John Wiley & Sons, Ltd.
Use of statistical models for evaluating antibody response as a correlate of protection against varicella
Authors: Chan Ivan S. F. , Li Shu , Matthews Holly , Chan Christina , Vessey Rupert , Sadoff Jerald , Heyse Joseph
Published: October 2002

In vaccine clinical trials, humoral antibody responses are often used to measure the effect of a vaccine because they correlate with a vaccine's protective efficacy against the target disease. While the concept of a correlate of protection usually refers to establishing a protective level of antibody titre, identifying a clear‐cut value is often impossible because vaccine efficacy is not related solely to the antibody titre. We propose examining the relationship between disease protection and the whole distribution of antibody responses rather than a single cut‐off level. In particular, we use failure‐time models to estimate the relationship between long‐term disease breakthroughs and primary antibody responses after vaccination. We apply these models to show that the varicella antibody response measured by glycoprotein enzyme‐linked immunosorbent assay 6 weeks after vaccination strongly correlate with protection against varicella (chickenpox); we used 7‐year follow‐up data from children who received one dose of a live attenuated varicella (Oka/Merck) vaccine. In addition, we explore the potential use of these models to predict long‐term disease breakthrough rates and to estimate the predicted vaccine efficacy of a similar varicella vaccine made with a modified manufacturing process. Copyright © 2002 John Wiley & Sons, Ltd.
Two approaches to mutation detection based on functional data
Authors: Pfeiffer Ruth M. , Bura Efstathia , Smith Amelia , Rutter Joni L.
Published: October 2002

A new technique, denaturing high‐performance liquid chromatography (dHPLC), allows for detection of any heterozygous sequence variation in a gene without prior knowledge of the precise location of the sequence change. The results of a dHPLC analysis are recorded in real‐time in the form of a chromatogram that is sequence‐specific. In this paper we present methods to classify an individual, based on the observed chromatogram, as a homozygous wild‐type or a carrier of a specific variant for the given DNA segment by comparison to representative chromatograms that are obtained from the training set of individuals with known variant status. The first approach consists of finding a parsimonious parametric model and then classifying each newly observed curve based on comparing the most discriminating characteristic, the main mode, to the main mode of the training curves. The second approach consists of finding empirical estimates of the modes of each chromatogram and using a bootstrap test for equality with the corresponding estimates of the training curves. We apply both methods to data on the breast cancer susceptibility geneBRCA1and test the performance of the methods on independent samples. Published in 2002 by John Wiley & Sons, Ltd.
Dealing with competing risks: testing covariates and calculating sample size
Authors: Pintilie Melania
Published: October 2002

It is universally agreed that Kaplan–Meier estimates overestimate the probability of the event of interest in the presence of competing risks. Kalbfleisch and Prentice recommend using the cumulative incidence as an estimate of the probability of an event of interest. However, there is no consensus on how to test the effect of a covariate in the presence of competing risks. Using simulations, this paper illustrates that the Cox proportional hazards model gives valid results when employed in testing the effect of a covariate on the hazard rate and when estimating the hazard ratio. A method to calculate the sample size for testing the effect of a covariate on outcome in the presence of competing risks is also provided. Copyright © 2002 John Wiley & Sons, Ltd.
Regression analysis based on pairwise ordering of patients' clinical histories
Authors: Follmann Dean A.
Published: October 2002

When a medical treatment influences a variety of outcomes, describing the global effect of treatment can be difficult. Traditional approaches specify how treatment affects each separate outcome. This can be done with separate models for each outcome, or by using a combined multivariate model. Describing the overall effect of a treatment thus requires combining these separate effects in some fashion and can be difficult to explain. In this paper, I specify a regression model for use with multiple outcomes where the outcome histories for each pair of patients are ranked. Pairs of patients with different lengths of follow‐up are evaluated solely over the common follow‐up interval. The logit of the probability that the outcome for patient i is better than that of patient j is assumed to depend on a linear function of the difference of the covariate vectors (for example, treatment indicators) for persons i and j. Thus covariates directly affect the entire clinical history, rather than directly affecting specific outcomes that comprise the history. The idea is that ranking outcomes is more relevant and interpretable than statistically combining separate effects. An estimating equations approach for estimation is described and an example of a clinical trial involving patients with heart failure is provided. Published in 2002 by John Wiley & Sons, Ltd.
Local likelihood analysis of the latency distribution with interval censored intermediate events
Authors: Bebchuk Judith D. , Betensky Rebecca A.
Published: October 2002

The distribution of time between an intermediate event and a terminal event is frequently of interest both in studying the behaviour of populations and in predicting outcomes for individuals. Current methods for estimating this latency distribution have either imposed assumptions on the hazard for the terminal event following the occurrence of the intermediate event or on the parametric form of the hazards. Here, local likelihood estimation is applied to the underlying hazard functions of a three‐state process in which the time of the intermediate event may be interval censored and the time of the terminal event is either observed or right censored. Smooth non‐parametric estimates of the latency distribution, along with bootstrap confidence intervals, are calculated, and tests for the comparison of two latency distributions are presented. The method is applied to two studies: a cohort of haemophiliacs who were infected with HIV by contaminated blood factor and followed for AIDS onset, and an AIDS clinical trial in which the intermediate event is the time to 50 per cent drop in CD4 count and the terminal event is AIDS or death. Simulations are presented to assess the performance of the estimation procedure. Copyright © 2002 John Wiley & Sons, Ltd.
Assessing chronic disease progression using non‐homogeneous exponential regression Markov models: an illustration using a selective breast cancer screening in Taiwan
Authors: Hsieh Hsin‐Ju , Chen Tony Hsiu‐Hsi , Chang Shu‐Hui
Published: October 2002

Previous research on estimation of the progression of chronic disease, from the normal preclinical screen‐detectable phase (PCDP) to the final clinical phase, has usually assumed constant transition rates and has rarely addressed how relevant covariates affect multi‐state transitions. The present study proposes two non‐homogeneous models using the Weibull distribution and piecewise exponential model, together with covariate functions of the proportional hazard form, to tackle these problems. We illustrate the models by application to a selective breast cancer screening programme. The results of the Weibull model yield estimates of scale and shape parameters for annual preclinical incidence rate as 0.0000058 (SE=0.0000019) and 2.4755 (SE=0.1153), the latter being significantly higher than 1. Annual transition rate was estimated as 0.3153 (SE=0.1385). Relative risks for the effects of late age at first pregnancy (AP) and high body mass index (BMI) on preclinical incidence rate were 1.98 and 2.59, respectively. The corresponding figures on the transition from the PCDP to clinical phase were 1.56 and 1.99, respectively. Non‐homogeneous Markov models proposed in this study can be easily applied to rates of progression of chronic disease with increasing or decreasing rates with time and to model the effect of relevant covariates on multi‐state transition rates. Copyright © 2002 John Wiley & Sons, Ltd.
An adaptive test of significance for a subset of regression coefficients
Authors: O'Gorman Thomas W.
Published: October 2002

An F‐test for a subset of regression coefficients is often used in order to compare two nested linear models. An adaptive test is proposed that has higher power than this F‐test for many non‐normal distributions of error terms. The adaptive test uses a weighted least squares procedure with weights determined from the Studentized deleted residuals from a linear model. A permutation method is then used so that the resulting test maintains its size near the nominal value. Results from several simulation studies are used to compare the power of the adaptive test to the F‐test. The adaptive test is recommended as a way of increasing the power of many common tests when used with models that have few parameters whenever the distribution of errors is non‐normal and the number of observations exceeds 20. Copyright © 2002 John Wiley & Sons, Ltd.
Choice of stratification in Poisson process analysis of recurrent event data with environmental covariates
Authors: Dewanji Anup , Moolgavkar Suresh H.
Published: October 2002

The Poisson process approach for studying the association between environmental covariates and recurrent events depends on the stratification of study period into intervals within which the baseline intensities are assumed constant. In this work we investigate the problem of bias and variance due to misspecification of this stratification. We suggest a cross‐validation approach to choosing a stratification model to balance the trade‐off between bias and variance. We also establish a connection between the Poisson process approach and case cross‐over studies. Copyright © 2002 John Wiley & Sons, Ltd.
Aggregate data meta‐analysis with time‐to‐event outcomes
Authors: Williamson Paula R. , Smith Catrin Tudur , Hutton Jane L. , Marson Anthony G.
Published: October 2002

In a meta‐analysis of randomized controlled trials with time‐to‐event outcomes, an aggregate data approach may be required for some or all included studies. Variation in the reporting of survival analyses in journals suggests that no single method for extracting the log(hazard ratio) estimate will suffice. Methods are described which improve upon a previously proposed method for estimating the log(HR) from survival curves. These methods extend to life‐tables. In the situation where the treatment effect varies over time and the trials in the meta‐analysis have different lengths of follow‐up, heterogeneity may be evident. In order to assess whether the hazard ratio changes with time, several tests are proposed and compared. A cohort study comparing life expectancy of males and females with cerebral palsy and a systematic review of five trials comparing two anti‐epileptic drugs, carbamazepine and sodium valproate, are used for illustration. Copyright © 2002 John Wiley & Sons, Ltd.
Estimation and projections of cancer prevalence from cancer registry data
Authors: Verdecchia Arduino , Angelis Giovanni De , Capocaccia Riccardo
Published: October 2002

A method, PIAMOD (Prevalence, Incidence, Analysis MODel), which allows the estimation and projection of cancer prevalence patterns by using cancer registry incidence and survival data is presented. As a first step the method involves the fit of incidence data by an age, period and cohort model to derive incidence projections. Prevalence is then estimated from modelled incidence and survival estimates. Cancer mortality is derived as a third step from modelled incidence, prevalence and survival. An application to female breast cancer is given for the Connecticut State by using data from the Connecticut Tumor Registry (CTR), 1973–1993. The age, period and cohort model fitted incidence quite well and allowed us to derive long‐term projections up to 2030. Patients' survival was also projected to future years according to a scenario approach based on two extreme hypotheses: steady, that is, no more improvements after 1993 (conservative), and continuously improving at the same rate as during the observation period. Age‐standardized estimated incidence shows a changing trend around the year 2005, when it starts decreasing. Age‐standardized prevalence is expected to increase and change trend at a later date. Breast cancer mortality is projected as decreasing, as the combined result of no further increase in incidence and improving cancer patients' survival. An easy‐to‐use PIAMOD software package, on which work is in progress, will be made available to individual cancer registries and/or health planning institutions or authorities once it is developed. The use of the PIAMOD method for cancer registries will allow them to provide results of paramount importance for the whole community involved in the assessment of future disease burden scenarios in an evolving society. Copyright © 2002 John Wiley & Sons, Ltd.
Detecting dose–response using contrasts: asymptotic power and sample size determination for binomial data
Authors: Bretz Frank , Hothorn Ludwig A.
Published: October 2002

Recently, Stewart and Ruberg proposed the use of contrast tests for detecting dose–response relationships. They considered in particular bivariate contrasts for healing rates and gave several possibilities of defining adequate sets of coefficients. This paper extends their work in several directions. First, asymptotic power expressions for both single and multiple contrast tests are derived. Secondly, well known trend tests are rewritten as multiple contrast tests, thus alleviating the inherent problem of choosing adequate contrast coefficients. Thirdly, recent results on the efficient calculation of multivariate normal probabilities overcome the traditional simulation‐based methods for the numerical computations. Modifications of the power formulae allow the calculation of sample sizes for given type I and II errors, the spontaneous rate, and the dose–response shape. Some numerical results of a power study for small to moderate sample sizes show that the nominal power is a reasonably good approximation to the actual power. An example from a clinical trial illustrates the practical use of the results. Copyright © 2002 John Wiley & Sons, Ltd.
‘I WAS AFRAID OF SAMUEL, THEREFORE I CAME TO SEKGOMA’: HERERO REFUGEES AND PATRONAGE POLITICS IN NGAMILAND, BECHUANALAND PROTECTORATE, 1890–1914
Authors: GEWALD JAN-BART
Published: October 2002

Writers dealing with the Herero of Botswana have tended mostly to deal with them as a single homogeneous whole. Concentrating on Ngamiland, this article outlines and discusses the arrival, at different times and for different reasons, of various groups of Herero into the territory. The article indicates that prior to the Herero–German war of 1904, the majority of Herero moved into Ngamiland on account of the activities of German colonizers and the Herero chief, Samuel Maharero. In Ngamiland, the Herero immigrants came to form a substantial source of support for the Batawana usurper, Sekgoma Letsholathebe. With the outbreak of the Herero–German war, Herero who had fled Namibia on earlier occasions now opposed the move of Samuel Maharero into Ngamiland, and found themselves supported by Sekgoma Letsholathebe. Following the deposition of Sekgoma in a coup, the position of Herero who had supported Sekgoma became increasingly tenuous and led to their move out of Ngamiland. Overall, the article presents a case study of the manner in which, in seeking to strengthen their positions within host communities, refugees of necessity come to be bound up in the internal politics of such communities.
CHARACTERISTICS OF CAPTIVES LEAVING THE CAMEROONS FOR THE AMERICAS, 1822–37
Authors: UGO NWOKEJI G. , ELTIS DAVID
Published: October 2002

On the basis of identifying the likely geographic origins of African names extracted from the Sierra Leone Liberated African registers, this essay estimates the provenance of the transatlantic slave trade that drew on the Cameroons estuary between 1822 and 1837. The sample, drawn from six separate vessels, is broken down by age and sex category and constitutes about 7 per cent of all Africans who left from the region in these years. It makes possible analysis of changes over time, comparisons of age and sex with distance between embarkation point and likely provenance zone, as well as interaction between Old Calabar and the Cameroons regions in the supply of slaves. The great majority of the captives originated within 200 miles of the coast and within 120 miles of the modern border with Nigeria.
OUT OF AFRICA
Authors: FEINBERG HARVEY M. , SOLODOW JOSEPH B.
Published: October 2002

This article traces the origins of the familiar quotation, ‘there is always something new coming out of Africa’. It demonstrates that the phrase was a proverb that originated in Greece no later than the fourth century BC. It charts the transmission of the phrase from Aristotle to the twentieth century, noting that Erasmus is the most important link in the Renaissance and that he may be responsible for the current form in which the phrase is used.

The article also shows that the meaning of the phrase was very different in ancient times from what it is today. Whereas ‘something new’ to Aristotle meant strange hybrid animals, current writers use the phrase with a sense of admiration.
THE SETTLERS' CATTLE COMPLEX: THE ETIQUETTE OF CULLING CATTLE IN COLONIAL ZIMBABWE, 1938
Authors: SHUTT ALLISON K.
Published: October 2002

This paper examines the 1938 cattle culling and sales in Gutu and Victoria reserves, colonial Zimbabwe. What began as a routine culling very quickly became a crisis of authority for the Native Affairs Department since critics of the Department forced an inquiry into the sales. The criticism and defence of the culling facilitated a debate on state and personal justice, as well as a dialogue about the proper behaviour towards Africans, settlers and animals. The critics of the cullings as well as the colonial officers all believed themselves to be experts in African affairs. Thus what began as a criticism of cattle culling revealed tensions within white society, and in particular the need to refashion boundaries of expertise and authority within the Native Affairs Department. A close examination of the scope and development of the ensuing commission of inquiry reveals the importance of etiquette to the colonial enterprise in colonial Zimbabwe.
A HISTORY OF GENOCIDE IN RWANDA
Authors: LEMARCHAND RENÉ
Published: October 2002

When Victims Become Killers: Colonialism,
Nativism and Genocide in Rwanda.
By MAHMOOD MAMDANI. Princeton NJ: Princeton
University Press, 2000. Pp. xvi+364. $29.95/£19.95 (ISBN 0-691-05821-0).
Bancroftian filariasis: a 13-year follow-up study of asymptomatic microfilariae carriers and endemic normals in Orissa, India
Authors: SAHOO P. K. , BABU GEDDAM J. J. , SATAPATHY A. K. , MOHANTY M. C. , DAS B. K. , ACHARYA A. S. , MISHRA N. , RAVINDRAN B.
Published: October 2002

The natural history of human filarial infections leading to development of disease has been a subject of intense debate. The models proposed so far have largely been based on cross-sectional data on microfilariae (Mf) and disease prevalence in filariasis endemic areas. In an attempt to study the parasitological and clinical consequences of filarial infection in Beldal (Orissa, India), an area endemic for Bancroftian filariasis, cohorts of 59 asymptomatic Mf carriers (AS) and 187 asymptomatic and amicrofilaraemic subjects or ‘endemic normals’ (‘EN’), were followed-up and a fraction (73% and 46% respectively) re-examined after 13 years to monitor (a) Mf prevalence, (b) Mf density, (c) circulating filarial antigen (CFA) and (d) chronic disease manifestations. The Mf prevalence and density were also monitored in Mf carriers after 1 and 4 years. Both Mf prevalence and density decreased progressively in the cohort of Mf carriers over a period of 13 years in Beldal. Only 37% of them continued to be microfilaraemic and the Mf density in these subjects was only 10% of the original level. However, loss of circulating Mf in this cohort did not result in loss of CFA and 95% remained CFA positive regardless of Mf status. About 23% of males in the ‘EN’ cohort developed hydrocoele while only 5·7% of male Mf carriers, who were not treated with DEC, had developed hydrocoele after 13 years. A cohort of Mf carriers in another area, Jatni, was also examined after 10 years to study the parasitological and clinical outcome. In this area, about 59% of the Mf carriers continued to be microfilaraemic after 10 years. These results reveal that in Mf carriers adult filarial worms persist for several years and that loss of circulating Mf with or without chemotherapy with DEC (single 12-day course) does not influence adult worm survival. The findings have been discussed in the context of ‘static’ and ‘dynamic’ models describing the relationship between infection and disease in human filariasis.
Host specificity of Trypanosoma (Herpetosoma) species: evidence that bank voles (Clethrionomys glareolus) carry only one T. (H.) evotomys 18S rRNA genotype but wood mice (Apodemus sylvaticus) carry at least two polyphyletic parasites
Authors: NOYES H. A. , AMBROSE P. , BARKER F. , BEGON M. , BENNET M. , BOWN K. J. , KEMP S. J.
Published: October 2002

The strongest evidence for host specificity of mammalian trypanosomes comes from parasites of the subgenus Trypanosoma (Herpetosoma). Laboratory studies have shown that T. (Herpetosoma) species will not infect an alternative host. However, this has not been demonstrated in wild populations. We screened 560 bank voles (Clethrionomys glareolus) and 148 wood mice (Apodemus sylvaticus) for trypanosomes by PCR amplification of the 18S rRNA gene. In total, 109 (19%) bank voles and 12 (8%) wood mice were infected. A HaeIII restriction site was discovered that could be used to discriminate between T. (H.) evotomys of the bank vole and T. (H.) grosi of the wood mouse. All the parasites in the bank voles were identified as T. (Herpetosoma) evotomys by RFLP-PCR. Out of the 12 wood mouse infections 10 were due to T. grosi. Two of the wood mice were infected with parasites with a novel genotype that was most similar to those of T. evotomys and T. microti of voles. Fifty-six fleas collected from the rodents were also screened for trypanosomes; 9 were infected with T. evotomys and 1 with T. grosi. One of the fleas infected with T. evotomys was collected from a wood mouse.
PCR detection of Tetramicra brevifilum (Microspora) infection in turbot (Scophthalmus maximus L.) musculature
Authors: LEIRO J. , IGLESIAS R. , PARAMÁ A. , ARAGORT W. , SANMARTÍN M. L.
Published: October 2002

This study investigated the spatial distribution of Tetramicra brevifilum spores in the musculature of infected turbot Scophthalmus maximus, with the aim of identifying the most appropriate body locations for diagnostic assays. A PCR protocol optimized for the detection of T. brevifilum spores in turbot muscle is also described. In fish showing low- and moderate-intensity infection, the spatial distribution of spores was best fitted by a negative binomial distribution, indicating a clumped spatial pattern; the negative binomial coefficient k was lower for fish with low-intensity infection, indicating a more markedly clumped pattern in these fish. In fish with high-intensity infection, the spatial distribution of spores was best fitted by the Poisson distribution, indicating a random pattern. In both low- and moderate-intensity infection, spores were present at highest density in the musculature adjoining the dorsal fins. Samples for PCR were therefore obtained from this location. PCR amplification was of the small subunit ribosomal DNA (SSUrDNA), using a pair of species-specific primers that amplify the 1250 bp product. The PCR protocol developed showed better sensitivity than microscopical techniques (detection rate by microscopy 25%, versus 42% by PCR), suggesting that it may be useful for routine screening for Tetramicra brevifilum infection in cultured turbot.
Recognition and invasion of human skin by Schistosoma mansoni cercariae: the key-role of L-arginine
Authors: HAAS W. , GRABE K. , GEIS C. , PÄCH T. , STOLL K. , FUCHS M. , HABERL B. , LOY C.
Published: October 2002

The attachment of Schistosoma mansoni cercariae to mammalian skin is specifically stimulated by L-arginine. As L-arginine is an unsuitable signal for a specific identification of mammalian skin we examined the following 5 hypotheses to explain the advantage of the cercarial sensitivity to L-arginine. (1) A Schistosoma infection lowered the arginine concentration in the serum of mice, and this could enable the cercariae to avoid attachments to already infected mice. However, the infection did not reduce the arginine concentration in the skin and the cercarial attachment responses to it. (2) Creeping cercariae showed chemotactic orientation specifically along increasing L-arginine gradients. L-arginine could act as a pheromone which could guide cercariae towards common penetration sites. However, the cercarial acetabular gland contents were not attractive and they did not (in contrast to previous reports) contain much arginine. (3) Schistosomula (transformed cercariae) could use L-arginine to produce nitric oxide (NO) for blood vessel dilation during their migration in the host. However, in vitro the transformed cercariae did not convert L-arginine into citrulline and NO. (4) Schistosomula could bind L-arginine from the surrounding tissues and so escape the cellular immune attack (which needs L-arginine as the precursor of NO). However, transformed cercariae bound no more L-arginine than L-serine and L-lysine. (5) Schistosomula, migrating parallel to the surface in the mammalian epidermis, are dependent on information on their position between the inner and the surface layers of the skin. In the mouse skin, they adjusted their body axis with the ventral side toward the deeper (arginine-residue rich) epidermis layers. When migrating in agar, they showed chemo-orientation toward serum, and D-glucose and L-arginine were the stimulating compounds therein. The burrowing schistosomula adjusted their body axis (as in the epidermis) with the ventral side toward the higher concentration of L-arginine and not of glucose. We argue that the sensitivity for L-arginine has its primary function in orientation within mammalian skin and in location of blood vessels.
The use of host specificity, pathogenicity, and molecular markers to differentiate between Gyrodactylus salaris Malmberg, 1957 and G. thymalli Zitnan, 1960 (Monogenea: Gyrodactylidae)
Authors: STERUD E. , MO T. A. , COLLINS C. M. , CUNNINGHAM C. O.
Published: October 2002

The validity of Gyrodactylus thymalli has been questioned, based on its morphological and genetic resemblance to G. salaris. This taxonomic problem has practical implications regarding correct diagnosis of G. salaris, which has proved to be highly pathogenic to stocks of wild Norwegian Atlantic salmon. The host specificity and pathogenicity of G. salaris and G. thymalli were experimentally tested on salmon and grayling. Both parasite species were able to infect, live and reproduce on both fish species. G. salaris was highly pathogenic for the experimental stock of salmon, while grayling mounted an effective response against this parasite. Both fish species responded to an infection with G. thymalli. The results did not support the hypothesis of conspecificity between G. thymalli and G. salaris. The ribosomal RNA gene intergenic spacer of both species was sequenced. Variation in sequence was lower than expected for different species. Variation in the sequences of tandemly repeated elements was found and may prove useful in distinguishing G. salaris and G. thymalli.
Characterization and cytochemical localization of an ATP diphosphohydrolase from Leishmania amazonensis promastigotes
Authors: COIMBRA E. S. , GONÇALVES-DA-COSTA S. C. , CORTE-REAL S. , DE FREITAS F. G. R. , DURÃO A. C. , SOUZA C. S. F. , SILVA-SANTOS M. I. , VASCONCELOS E. G.
Published: October 2002

An ATP diphosphohydrolase was identified in the plasma membranes isolated from promastigote forms of Leishmania amazonensis. Both ATP and ADP were hydrolysed at similar rates by the enzyme. Other nucleotides such as UTP, GTP and CTP were also degraded, revealing a broad substrate specificity. Adding ATP and ADP simultaneously, the amount of hydrolysis achieved was compatible with the presence of a single enzyme. ATPase activity was not affected by addition of vanadate, ouabain, thapsigargin, dicyclohexylcarbodiimide, oligomycin and bafilomycin A, thus excluding involvement of P-, F- and V-type ATPases. The effects of pH in the range 6·5–8·5 were examined using ATP or p-NPP as substrate. At pH 7·4, the phosphatase activity decreased, and did not show a significant contribution to ATP hydrolysis. In addition, the enzyme was not inhibited by levamisole and ammonium molybdate, excluding alkaline phosphatase and nucleotidase activities, respectively. Sodium azide (5–10 mM) caused inhibition of the ATP and ADP hydrolysis in a dose-dependent manner. Calcium was the best activating metal ion for both ATPase and ADPase activities. Ultrastructural cytochemical microscopy showed ATP diphosphohydrolase on the surface and flagellar pocket of the parasite. We have proposed that L. amazonensis ATP diphosphohydrolase may participate in the salvage pathway of nucleosides.
Experimental evidence of hybrid breakdown between the two geographical strains of Schistosoma intercalatum
Authors: PAGÈS J. R. , SOUTHGATE V. R. , TCHUEM TCHUENTÉ L. A. , JOURDANE J.
Published: October 2002

Reciprocal crosses (Schistosoma intercalatum male Zaire×S. intercalatum female Cameroon: S. intercalatum female Zaire×S. intercalatum male Cameroon) were produced in 10 mice by exposing each mouse to 60 male cercariae of one isolate and 60 female cercariae of the other isolate, and vice versa. Hybrid generations originating from the two crosses were established. The infectivity of the F1, F2, F3 and F4 hybrid generations were evaluated after exposing snails individually to 5 miracidia. A comparative histological study of snails infected with F2 and F4 hybrid sporocysts from both crosses was made to assess abnormalities in the intramolluscan development of the hybrids. The worm recovery rate and fecundity were measured by comparing the fitness of the mid-parents with that of the hybrids. S. intercalatum Cameroon was compatible with Bulinus forskalii and incompatible with B. globosus whereas S. intercalatum Zaire was compatible with B. globosus and incompatible with B. forskalii. In the case of S. intercalatum male Cameroon×S. intercalatum female Zaire, hybrid miracidia develops in both B. forskalii and B. globosus in F1, F2 and F3 generations. The infection rate was much lower for B. globosus and F2 and F3 generations produced few cercariae (less than 30 cercariae in overall per snail) and F4 miracidia were only infective to B. forskalii again producing few cercariae. At 40 days post-infection the sporocyst contains masses of acidophilic granules originating from the breakup of pycnotic nuclei. Similarly the F1, F2 and F3 miracidia of the reciprocal cross (S. intercalatum male Zaire×S. intercalatum female Cameroon) exhibited a dual infectivity for B. forskalii and B. globosus, but cercarial productivity was low (less than 30 cercariae overall per snail for F2 and F3 generations). Histological studies demonstrated sporocyst degeneration in snails infected with F4 generation. In the definitive host, the F1 generation (both crosses) exhibited hybrid vigour in that the worm return was greater than that of the mid-parent, F2 and F3 generations. No significant difference in fecundity was demonstrated between the parental strains and the F1 and F2 generations, yet egg production of the F3 generation was significantly lower. It is apparent that there is a post-zygotic barrier in the crosses of S. intercalatum Zaire and S. intercalatum Cameroon from the F2 generations onwards, and sterility of the F4 hybrid sporocyst supports the concept of the existence of 2 distinct taxa.
Field evidence for density-dependent facilitation amongst Ixodes ricinus ticks feeding on sheep
Authors: OGDEN N. H. , CASEY A. N. J. , FRENCH N. P. , ADAMS J. D. W. , WOLDEHIWET Z.
Published: October 2002

Engorged Ixodes ricinus nymphs collected from sheep resident in an upland UK field site were significantly lighter than nymphs that engorged on previously tick-naïve sheep, indicating that site-resident sheep continually exposed to ticks acquired anti-tick resistance. The weights of engorged nymphs that fed on naturally tick-resistant sheep increased significantly, however, when increasingly high numbers of adult female ticks fed on the sheep during seasonal peaks of tick activity. This relationship was unaffected by variations in nymph weight amongst individual sheep, between seasons and years, and potential effects of sheep infection with Ehrlichia phagocytophila; this suggests that high adult tick infestations may directly inhibit the expression of acquired anti-tick resistance by sheep. The length, width and weight of adult ticks and the scutum length of adult females were linearly related to their weight as an engorged nymph. The mean scutum length of adult female ticks feeding on sheep in the field site was greater than that of adult females obtained from engorged nymphs collected from sheep of the same site. This suggests that larger ticks have a survival advantage and that I. ricinus ticks exhibit density-dependent intraspecific facilitation at high infestation levels with potential consequences for the transmission of tick-borne diseases.
Chromosomal size variation in Trypanosoma cruzi is mainly progressive and is evolutionarily informative
Authors: HENRIKSSON J. , DUJARDIN J. C. , BARNABÉ C. , BRISSE S. , TIMPERMAN G. , VENEGAS J. , PETTERSSON U. , TIBAYRENC M. , SOLARI A.
Published: October 2002

The evolutionary significance of chromosome size polymorphism was explored in a representative panel of 26 Trypanosoma cruzi stocks. We tested a progressive model (aCSDI) assuming that the larger the size difference between homologous chromosomes, the more divergent the parasites are. This was contrasted with a non-progressive model (Jaccard's distance), in which any chromosome size difference has the same weight. ACSDI-based dendrograms were very similar to those built-up from multilocus enzyme electrophoresis (MLEE) and random amplified polymorphic DNA (RAPD) data: structuring in 2 major lineages (T. cruzi I and T. cruzi II) and 5 small subdivisions within T. cruzi II was identical, and branching was very similar. Furthermore, a significant correlation (P<0·001) was observed between aCSDI and phenetic distances calculated from MLEE and RAPD data. In contrast, analysis of chromosome size polymorphism with Jaccard's distance generated dendrograms with relatively long branches, causing most branching points to cluster close together, which generates statistically uncertain branching points. Our results thus support a model of progressive chromosome size-variation and show that despite an extensive polymorphism, chromosomal sizes constitute valuable characters for evolutionary analyses. Furthermore, our data are consistent with the clonal evolution model previously proposed for T. cruzi.
Needle in a haystack: involvement of the copepod Paracartia grani in the life-cycle of the oyster pathogen Marteilia refringens
Authors: AUDEMARD C. , LE ROUX F. , BARNAUD A. , COLLINS C. , SAUTOUR B. , SAURIAU P-G. , DE MONTAUDOUIN X. , COUSTAU C. , COMBES C. , BERTHE F.
Published: October 2002

Marteilia refringens is a major pathogen of the European flat oyster, Ostrea edulis Linnaeus. Since its description, the life-cycle of this protozoan parasite has eluded discovery. Attempts to infect oysters experimentally have been unsuccessful and led to the hypothesis of a complex life-cycle involving several hosts. Knowledge of this life-cycle is of central importance in order to manage oyster disease. However, the exploration of M. refringens life-cycle has been previously limited by the detection tools available and the tremendous number of species to be screened in enzootic areas. In this study, these two restrictions were circumvented by the use of both molecular detection tools and a mesocosm with low biodiversity. Screening of the entire fauna of the pond for M. refringens DNA was systematically undertaken using PCR. Here, we show that the copepod Paracartia(Acartia) grani is a host of M. refringens. Not only was DNA of M. refringens consistently detected in P. grani but also the presence of the parasite in the ovarian tissues was demonstrated using in situ hybridization. Finally, successful experimental transmissions provided evidence that P. grani can be infected from infected flat oysters.
The Plasmodium falciparum var gene switching rate, switching mechanism and patterns of parasite recrudescence described by mathematical modelling
Authors: PAGET-MCNICOL S. , GATTON M. , HASTINGS I. , SAUL A.
Published: October 2002

Recrudescing Plasmodium falciparum parasitaemia is attributed to the switching of PfEMP1, a variant antigen family encoded by the var gene repertoire, and the host's immune response. We have developed a mathematical model which incorporates var gene switching, and variant specific, non-variant specific and non-specific immunity. By conducting a sensitivity analysis of the model we have defined the parameter limits which produce chronic and recrudescing infections. We explore 3 switching mechanisms: ordered, random and uncoupled switching. We show that if var genes switch on and off independently at variable rates through the repertoire a chronic clinical infection is predicted. The fastest switching-on rate that produces a chronic infection is 0·03% per generation. The model predicts that non-variant specific immunity plays an important role in reducing disease severity. This work illustrates the complex relationship between the malaria parasite and its host and shows that var gene switching at rates substantially slower than 2% are essential for parasite survival.
Two main clusters within Trypanosoma cruzi zymodeme 3 are defined by distinct regions of the ribosomal RNA cistron
Authors: MENDONÇA M. B. A. , NEHME N. S. , SANTOS S. S. , CUPOLILLO E. , VARGAS N. , JUNQUEIRA A. , NAIFF R. D. , BARRETT T. V. , COURA J. R. , ZINGALES B. , FERNANDES O.
Published: October 2002

Trypanosoma cruzi is currently classified into 2 major phylogenetic lineages, T. cruzi I and II, that correlate with the formerly described zymodeme 1 and 2, respectively. Another isoenzymic group (zymodeme 3–Z3) was also described. In this study, we analysed the genetic diversity among Z3 isolates of the Brazilian Amazon by restriction fragment length polymorphism of the intergenic transcribed spacers (ITSs) of the ribosomal RNA cistron and the size of the divergent domain D7 of the 24Sα rRNA gene. DNAs from 12 T. cruzi Z3 isolates obtained from humans (2), Panstrongylus geniculatus (1), and Rhodnius brethesi (9) were submitted to PCR amplification of the ITSs plus the 5·8S rDNA. The PCR products were digested with 4 distinct endonucleases and the profiles analysed by a numerical methodology. The phenetic dendrogram revealed a clear dichotomy in the Z3 group, defining 2 groups that were named Z3-A and Z3-B. Dimorphism was also found in the band sizes of the amplified D7 divergent domain of the 24Sα rDNA, which showed a perfect correlation with the ITSs clustering. The organization of the ribosomal cistron was investigated by Southern blotting and shown to be conserved in the genome of the 2 Z3 groups. This study shows that the rDNA cistron allows the definition of 2 distinct subclusters in Z3 isolates.
Ultrastructure of Buddenbrockia identifies it as a myxozoan and verifies the bilaterian origin of the Myxozoa
Authors: OKAMURA B. , CURRY A. , WOOD T. S. , CANNING E. U.
Published: October 2002

The phylogenetic affinities of Buddenbrockia, a nematode-like parasite of freshwater bryozoans, have remained unknown since it was first reported in the nineteenth century. The discovery of Buddenbrockia parasitic in Hyalinella punctata in Ohio and Plumatella repens in France has provided material for the first ultrastructural study of this animal. This has revealed the presence of polar capsules, diagnostic myxozoan features, in the body wall. Other features, which place Buddenbrockia firmly among tetracapsulid myxozoans in the Class Malacosporea, are the unusual morphology of the polar capsules, the absence of the external tube in capsulogenesis, the body wall with its unusual cell junctions and utilization of freshwater bryozoans as hosts. The ultrastructural study has established the triploblastic organization of Buddenbrockia by confirmation of the presence of an inner layer of cells and 4 sets of longitudinal muscles. Our studies have, thus, simultaneously revealed that Buddenbrockia is a myxozoan and that the myxozoans are derived from bilaterians. The latter conclusion resolves the ongoing controversy over the triploblastic versus diploblastic nature of the Myxozoa. Our studies also provide evidence that bryozoans are ancestral hosts for the myxozoans and that loss of triploblast features has characterized the major radiation of the better known endoparasites of fish and worms in the Class Myxosporea.