Group Mean Analysis Research Articles

Genetic diversity and differentiation of Leptosphaeria biglobosa on oilseed rape in China

Phoma stem canker (blackleg), caused by the fungi Leptosphaeria maculans and L. biglobosa, is the most devastating disease in oilseed rape (canola) production worldwide. In this study, 84 Leptosphaeria isolates were collected in China from rapeseed (Brassica napus) plants with blackleg symptoms and identified using multiplex PCR and rDNA-ITS sequence analysis. Results showed that all these isolates are L. biglobosa and no L. maculans was detected. A total of 99 isolates was analyzed, including 15 other L. biglobosa isolates from the UK, Canada and Poland using rDNA-ITS sequences, and all isolates were found to belong to the L. biglobosa 'brassicae' subclade. The genetic variation of these 99 isolates was tested using ISSR (inter simple sequence repeats) markers using 24 polymorphic primers pairs that generated 241 bands by ISSR-PCR amplification. A dendrogram based on weighted pair group mean analysis of these bands revealed that L. biglobosa isolates from China clustered into different groups from those obtained from Canada and Europe. Furthermore, Chinese isolates from seven provinces, except those from Jiangsu, could be placed within the same cluster, based on geographical location. Nei’s gene diversity ranged from 0.25 in Jiangsu to 0.11 in Sichuan, and Shannon’s information index from 0.16 to 0.37. Genetic identity ranged from 0.784 to 0.834 when isolates from China were compared with those from Canada and the UK, respectively. Analysis of gene flow among populations (Nm) indicated that almost no gene exchange has occurred between L. biglobosa in China and the populations of the fungus from the UK or Canada.

Atmospheric moisture effects on the testing rate and cementation seating load following resin-strengthening of a soda lime glass analogue for dental porcelain

ObjectivesTo investigate if resin-cementation of a soda lime glass dental analogue could elucidate information regarding the pattern of resin-reinforcement when coated in an environment actively scavenged of moisture. Methods192 soda lime disc-shaped specimens (alumina particle air abraded, hydrofluoric acid-etched and silane coated) were randomly assigned to eight groups (n=24 per group) prior to resin-coating at seating loads of 5N (Groups A–D) and 30N (Groups E–H) in an environment where moisture was actively scavenged and maintained below 15ppm. Following one week storage the discs were tested in biaxial flexure at crosshead rates of 0.01, 0.1, 1 and 10mm/min. Analysis of group means was performed utilising a general linear model univariate analysis and post hoc all paired Tukey tests (P<0.05). ResultsThe general linear model univariate analysis identified the mean biaxial flexure strength (BFS) was significantly influenced by the factors resin-cementation seating load (P<0.001) and crosshead speed of the applied load (P<0.001) with a significant interaction (P=0.008) between both factors. The linear logarithmic regression curves fitted to the group mean BFS data plotted against the crosshead speed highlighted significant differences between the pattern of resin-strengthening for the cementation loads and testing conditions. ConclusionsThe decrease in resin-penetration expected within the ‘resin-ceramic hybrid layer’ following removal of the 30N seating load was proposed as the modifying resin-strengthening parameter. These observations are supported by the viscoelastic and creep behaviour of resins at slow testing rates which becomes the dominant or determining phenomenon.

Gender differences in both tails of the distribution of numerical competencies in preschool children

Gender differences in mathematical achievement have been examined in a wide range of age groups but only a few studies addressed this issue in preschool children. We compared preschool girls (n = 570) and boys (n = 524) from Germany with regard to numerical competencies. Differences in overall group means and the frequency of representation at low, middle, or high levels of performance were explored for girls and boys. Analysis of overall group means revealed that boys showed a better performance than girls (d = .32). The analysis of frequencies showed differences in both tails but not in the middle of the distribution of numerical competencies. While boys were more often found at higher levels of performance, girls were found to be overrepresented in the low-ability end of the distribution. These findings demonstrate that gender differences in mathematical achievement can emerge before school entry and stress the importance of further research looking for gender divides in mathematical achievement in preschool children from different countries as well as possible underlying factors.

Genetic diversity and structure of the Fusarium oxysporum f.sp. lini populations on linseed (Linum usitatissimum) in China

The genetic diversity of specific Fusarium oxysporum f.sp. lini from six provinces in China was investigated using molecular markers, inter-simple sequence repeats (ISSR). Based on the morphological features and the internal transcribed spacer (ITS) sequences, 96 isolates were identified as Fusarium oxysporum. The 96 isolates were amplified by PCR with 12 ISSR primers. The number of bands amplified by each primer ranged from 43 to 142, with sizes ranging from 250 to 4,500 bp. A total of 800 bands were observed, out of which 797 were polymorphic (99.62%). The percentage of polymorphic loci varied from 17.25% in Gansu and Inner Mongolia to 33.75% in Sinkiang. Nei’s gene diversity index (h) ranged from 0.0428 in Gansu to 0.0666 in Sinkiang, and Shannon’s information index (I) ranged from 0.0675 in Gansu to 0.1117 in Sinkiang. The genetic identity using the Nei’s genetic identity varied from 0.9643 between the populations from Hebei and Gansu to 0.9844 between the populations from Sinkiang and Shanxi. Unweighted pair group mean analysis (UPGMA) cluster analysis, as indicated by the Nei’s genetic distance, showed the distances ranging from 0.0158 between the populations from Sinkiang and Shanxi to 0.0364 between the populations from Hebei and Gansu. The six populations were clustered into three subgroups. The Gansu population was clustered into one subgroup, the same as the Inner Mongolia population. The four other populations were clustered into the third subgroup. The Nei’s GST (0.2972) and gene flow among populations (Nm =1.1825) revealed large gene exchanges among populations.

Testing rate and cementation seating load effects on resin-strengthening of a dental porcelain analogue

ObjectivesTo determine the resin-strengthening dependence of a soda-lime-glass analogue for dental porcelain as a function of biaxial flexure strength (BFS), test crosshead rate and cementation seating load. MethodsDisc-shaped soda-lime glass specimens were divided into twelve groups (n=24), alumina particle air abraded and hydrofluoric acid-etched. Specimens (Groups A–D) were stored in a desiccator prior to testing at crosshead rates of 0.01, 0.1, 1 and 10mm/min, respectively. The remaining specimens were silane treated, Rely-X Veneer resin-coated with a seating load of 5N (Groups E–H) and 30N (Groups I–L) prior to light irradiation at 480±20mW/cm2, 24h dry storage and BFS testing at 0.01, 0.1, 1 and 10mm/min, respectively. A linear logarithmic regression curve was fit to the raw data to elucidate static fatigue effects of the soda-lime-glass. Analysis of group means was performed utilising a general linear model univariate analysis and post hoc all paired Tukey tests (P<0.05). ResultsThe linear logarithmic regression curve demonstrated the static fatigue effects of the soda-lime-glass analogue. Rely-X Veneer resin-coating (Groups E–L) resulted in significant increases in the mean BFS data for all crosshead rates examined (all P<0.001). However, the pattern of rate dependence effects on resin-cementation deviated from the log relationship observed with the uncoated controls. ConclusionThis study further highlights that when slow crack growth is simulated during testing, valuable insights into the significant modification of a hereto well described phenomenon such as resin-strengthening mediated by the resin–ceramic hybrid layer is provided.

Can Electroacupuncture Affect the Sympathetic Activity, Estimated by Skin Temperature Measurement? A Functional MRI Study on the Effect of Needling at GB 34 and GB 39 on Patients with Pain in the Lower Extremity

The Purpose of this study was to investigate the possible needling effect on sympathetic activity by using functional MRI (fMRI). Twelve patients with left lower extremity pain were enrolled in our study. Each was given deep needling at left GB34 (yanglingquan) and GB39 (xuanzhong) points simultaneously. All patients got the strong DeQi sensation by manipulating the needles, and then electroacupucture (EA) was given and lasted for thirty minutes before fMRI scan. Then the fMRI scan was performed by scanning the whole brain with five blocks lasting 2 minutes each. The patients' palm skin temperatures were tested every five minutes as indication of the sympathetic activity from the beginning of EA to the end of our fMRI scan. Functional images were processed by using FEAT software at different levels including the simple single subject analysis, multi-subjects group mean analysis, and multi-subjects unpaired two difference analysis. Finally, 9 of 12 patients' palm temperatures increased gradually but the other three decreased. In comparison of two different palm skin temperature change groups, more significant activation over bilateral caudate head, right lentiform and periaqueductal gray (PAG) were found in the temperature-increased group, but palm temperature-decreased patients revealed more significant activation over bilateral anterior cingulated cortex (ACC), insula, primary somatosensory gyrus (SI), orbitofrontal cortex, occipital cortex, hippocampus and amygdala formation. Our study suggested that needling at analgesic points may modulate the sympathetic activity and such evident difference on brain responses may correlate with the clinical analgesia effects.

Genetic diversity and population differentiation of chestnut blight fungus, Cryphonectria parasitica, in China as revealed by RAPD

Seventeen Cryphonectria parasitica populations sampled from six regions in China were investigated using RAPD. Across all 169 isolates from the 17 populations evaluated, 52 of the 71 markers (73%) were polymorphic, total genetic diversity (h) was 0.1463, and Shannon's index was 0.2312. Diversity within populations accounted for 74% of total genetic diversity, and genetic differentiation among populations was 0.26 (G (ST) = 0.26). Gene flow was 1.4 among the populations; higher gene flow was found among populations within regions and among regions [N (m) (G (SR)) = 2.8 and N (m) (G (RT)) = 3.5]. The unweighted pair group mean analysis (UPGMA) dendrogram revealed two distinct clusters: the northern China group and the southern China group. The spatial autocorrelation analysis revealed that the variation at most loci was randomly distributed and lacked spatial structure, but several loci and closer distances were spatially structured. Human activity and habitat could also be important factors affecting genetic structure among C. parasitica populations in China. Genetic diversity was highest in Southwest China, descending in an orderly fashion to Northeast China. This pattern indicated that Southwest China might be the center of origin of C. parasitica in China. The present study provides useful information for understanding the origin and spread of chestnut blight fungus in China and valuable data for formulating relevant strategies for controlling the disease in China.

Motivational Interviewing to Increase Physical Activity in Long-Term Cancer Survivors

Physical activity can confer many benefits on cancer survivors, including relief of persistent symptoms related to cancer treatment. To evaluate the effect of a motivational interviewing (MI) intervention on increasing physical activity (Community Healthy Activities Model Program for Seniors questionnaire) and improving aerobic fitness (6-minute walk), health (Medical Outcomes Study Short-Form 36), and fatigue (Schwartz Cancer Fatigue Scale) in cancer survivors. A secondary purpose was to evaluate whether the effect of MI on physical activities depended on self-efficacy. Fifty-six physically inactive adult cancer survivors (mean=42 months since completion of treatment) were assigned randomly to intervention and control groups. The MI intervention consisted of one in-person counseling session followed by two MI telephone calls over 6 months. Control group participants received two telephone calls without MI content. Outcomes were measured at baseline, 3 months, and 6 months, and were analyzed using multilevel modeling. The results of the MI intervention explained significant group differences in regular physical activities (measured in caloric expenditure per week), controlling for time since completion of cancer treatment (p<.05). Aerobic fitness, physical and mental health, and fatigue were not different between groups. In the intervention group, individuals with high self-efficacy for exercise at baseline increased their physical activity more than those with low self-efficacy (p<.05). In the control group, increases in physical activity did not depend on self-efficacy. Use of MI may increase physical activity in long-term cancer survivors, especially in persons with high self-efficacy for exercise. Multilevel modeling analysis revealed individual changes that would not have been shown by analysis of group means. Future studies with larger samples or more intense MI interventions may show changes in aerobic fitness, physical and mental health, and fatigue.

A comparison of peak expiratory flow measured from forced vital capacity and peak flow meter manoeuvres in healthy volunteers

BACKGROUND:Spirometry measures the mechanical function of lungs, chest wall and respiratory muscles by assessing the total volume of air exhaled from total lung capacity to residual volume. Spirometry and peak flow measurements have usually been carried out on separate equipments using different expiratory maneuvers.AIMS:The present study was carried out to determine whether there is a significant difference between peak expiratory flow (PEF) derived from a short sharp exhalation (PEF maneuver) and that derived from a full forced vital capacity (FVC) maneuver in healthy volunteers.SETTINGS:A medical college and tertiary level hospital.MATERIALS AND METHODS:The present study was carried out during the period from January 2006 to July 2006. The study included 80 healthy volunteers with no coexisting illnesses, who were in the 15-45 years age group and belonging to either sex. They were asked to perform two sets of PEF and FVC maneuvers using the same turbine spirometer; the order was randomly assigned.STATISTICAL ANALYSIS:The difference between PEF obtained from a peak flow maneuver (PEFPF) and that obtained from a forced vital capacity maneuver (PEFVC) in healthy volunteers was analyzed separately for males and females, as well as for both groups combined, and statistical significance of its correlations with study data parameters was analyzed.RESULTS:The difference between PEF obtained from a peak flow maneuver (PEFPF) and that obtained from a forced vital capacity maneuver (PEFVC) was statistically significant (P < 0.001) in males and in females separately and also for both groups combined. PEFPF (517.25 ± 83.22 liters/min) was significantly greater than PEFVC (511.09 ± 83.54 liters/min), as found on combined group mean analysis. However, the difference was small (6.16 + 7.09 liters/min).CONCLUSIONS:FVC maneuver can be used over spirometers to detect the PEF; and on follow-up subsequently, the same maneuver should be used to derive PEF. If we are using a peak flow maneuver subsequently, corrections are required to compensate for the difference due to the different maneuver.

Neuronal Specificity of Needling Acupoints at Same Meridian: A Control Functional Magnetic Resonance Imaging Study with Electroacupuncture

The purpose of this study was to investigate the neuronal specificity of needling acupoints at same meridian by functional Magnetic Resonance Imaging (fMRI). The selected acupoints GB34 (Yanglinquan) and GB39 (Xuanzhong) were at the same gallbladder meridian based on traditional Chinese medicine. In our study we devise three distinct EA (electroacupuncture) manipulations: real EA (deep needling at acupoints), sham EA (deep needling at no-meridian points) and shallow EA (subcutaneous needling at acupoints). Twelve healthy volunteers with right-handiness were enrolled and received three different EA manipulations in counter-balanced orders. DeQi scores were used to evaluate the degree of needling sensation. We found real EA can induce significant stronger needling sensation than sham EA and shallow EA. Multisubjects group mean analysis showed that pain-related cortex including primary and secondary somatosensory cortex (SI and S II), anterior cingulated cortex (ACC), insula were involved in three EA stimulation. Bilateral activation of prefrontal gyrus and occipital cortex were exclusively found in real EA. Deactivation over the rostral segment of ACC was also shown in real and shallow EA. Further paired two difference analysis indicated that real EA induced higher activation than sham EA over bilateral prefrontal gyrus, right-side occipital gyrus and deactivation over the rostral segment of ACC. In the comparing with real EA versus shallow EA, there was right-side activation over the SI, S II, motor cortex, ACC, insula, thalamus, hippocampus, occipital cortex, and cerebellum; also activation over bilateral prefrontal gyrus, caudate and pons. Although no significant activation was found over periaqueductal gray (PAG), further analysis showed the mean and maximal signal changes were different under three EA manipulations. We concluded that EA at analgesic acupoints of same meridian maybe involved the pain-related neuromatrix especially the hypothalamus-limbic system; deep EA at meridian points could elicit stronger needling sensation and modulate the pain-related neuromatrix more effectively than EA at nonmeridian points or shallow EA at meridian points.

Tracking the Development of Professional Values in Undergraduate Nursing Students

In the current nursing shortage, nurses are frequently making significant patient care decisions concerning value-laden clinical issues. A program evaluation study was conducted to track professional values over time from entry into a baccalaureate program to graduation. Nursing students completed a survey measuring professional values upon entry into and exit from the program. Comparative analysis of pretest and posttest group means demonstrated statistically significant increases in total scores. The highest pretest value items were also the highest on the posttest, with the addition of patient advocacy. Patient advocacy jumped 16 places from pretest to posttest to become the highest-ranked statement upon exit from the program. All of the values rated as least valued at pretest remained least valued at posttest; however, the means of all but two (participating in nursing research and providing consumer education about products/services) increased significantly. The value statements with mean scores that increased significantly centered on aspects of nursing practice less visible to the lay public and involving interaction with other health care providers.

“My father knows the minister”

PurposeThe purpose of this paper is to fill a gap in the literature on Arab women's conceptions of leadership. By comparing women's leadership authority values in three Arab countries, the paper aims to refine existing gender‐neutral research on leadership in the “Arab world”.Design/methodology/approachThe study involved administering a survey, which had been developed based on Weber's work on authority (1978) and contemporary discussions of implicit leadership theories (ILT). The data (n=320) were drawn from female subjects who were enrolled in upper‐division business major classes in three countries, Oman, Lebanon and the UAE The women thus constituted educated entrants to their respective labor markets. The data were subjected to an analysis of group means on each of the questions, using the Scheffe option available in ANOVA.FindingsThe analysis found evidence of common leadership authority values in the Gulf countries (Oman and the UAE). Lebanon, meanwhile, was distinguished by relatively low levels of “traditional” authority, and very high levels of “charismatic” authority. The findings demonstrate important regional similarities and difference in leadership authority values in the “Arab world.”Research limitations/implicationsThe study is limited by the number of countries studied. It is thus anticipated that future comparative research will be extended to include other countries (both Arab and non‐Arab), and men.Practical implicationsLeadership training in the Arab region must be sensitized and tailored to address regional and gender‐specific conceptions of leadership.Originality/valueThe paper challenges and refines widespread meta‐notions and analyses of the “Arab world” and “Arab leadership.”

PREVENTIVE EFFECTS OF GARLIC EXTRACT ON LIPID PEROXIDATION AND ANTIOXIDANT DEFENCE SYSTEM IN N-NITROSODIETHYLAMINE INDUCED HEPATOCARCINOGENESIS IN RATS

ISHS III WOCMAP Congress on Medicinal and Aromatic Plants - Volume 6: Traditional Medicine and Nutraceuticals PREVENTIVE EFFECTS OF GARLIC EXTRACT ON LIPID PEROXIDATION AND ANTIOXIDANT DEFENCE SYSTEM IN N-NITROSODIETHYLAMINE INDUCED HEPATOCARCINOGENESIS IN RATS

NITROGEN CHANGES AND DOMAIN BACTERIA RIBOTYPE DIVERSITY IN SOILS OVERLYING THE CENTRALIA, PENNSYLVANIA UNDERGROUND COAL MINE FIRE

In this study, changes to soil chemistry and domain bacteria diversity were analyzed in a near-surface environment recently impacted by the Centralia, Pennsylvania anthracite coal mine fire. As this underground fire expands into new areas, land collapses are common as hot gases vent to the surface, causing rapid changes in surface soil temperatures and chemistry. To determine how these environmental changes are affecting the resident microbial populations, surface soil samples (at a depth of 0-20 cm) were taken from boreholes at eight locations that spanned both newly affected and unaffected areas. Soil temperature, pH, and chemical composition were analyzed at each borehole. Terminal restriction fragment length polymorphism analysis of domain bacteria 16S rRNA genes was utilized to monitor the associated changes in soil microbial diversity. Over a 1-year period, the maximum surface soil temperatures in this site increased from 47.0 °C to 75.7 °C. Whereas ribotype diversity did decrease significantly within individual boreholes as temperatures increased, no significant correlation was observed between overall temperature increases and either soil chemistry or domain bacteria ribotype diversity. Unweighted pair group means analysis of Jaccard ribotype similarity coefficients indicated that soil bacterial community diversity clustered well with trends in temperature, ammonium, and nitrate levels. Since significantly elevated ammonium and nitrate levels were seen in several of the affected boreholes, polymerase chain reaction with primers specific for ammonia-oxidizing bacteria and Tap-terminal restriction fragment length polymorphism analysis of the ribotype profiles were performed. These analyses provided evidence that nitrifying bacteria were present throughout the site.

Genetic Relationship and Clustering of Some Sugarcane Genotypes Based on Esterase, Peroxidase and Amylase Isozyme Polymorphism

Three isozyme systems viz. esterase, peroxidase and amylase were assayed electrophoretically from extracts of leaf tissues of some elite genotypes of India to unravel their genetic relationship. Twenty five isozyme phenotypes were resolved in the 9 genotypes; 8 in esterase (EST), 12 in peroxidase (POX) and 5 in amylase (AMY). The genotypes could be distinguished on the basis of polymorphic isozyme spectra and multimeric isozyme profiles. The most polymorphic isoenzyme system was peroxidase (POX), which provided a discriminatory tool for evaluating and characterizing genotypes. The banding similarly index based on the number of polymorphic bands common between each genotype pair, ranged from 0.38 to 0.89. The genotypes were clustered in 2 distinct groups having 3 and 6 genotypes each by subjecting the genetic dissimilarity between them to UPGMA (Unweighted Pair Group Mean Analysis) statistical treatment and bootstrap analysis. The consistency Index of 8 different nodes present in phenogram representing percentage useable isozyme loci per node showed the node 8 to be the most important and consistent node followed by the node 6. Some esterase and peroxidase isozyme phenotypes were specific to the genotypes and were found to be suitable for cultivar identification.

Burkholderia pseudomallei strain type, based on pulsed-field gel electrophoresis, does not determine disease presentation in melioidosis

Melioidosis, the infection due to Burkholderia pseudomallei, may present with a spectrum of severity and may affect any site in the body. Differential strain virulence and tropism suggested by previous studies would have implications for virulence and vaccine work. We explored clinical correlations using pulsed-field gel electrophoresis (PFGE) typing in a well-characterised clinical collection. Two methods of analysis were used based on band-based similarity values: first, a conventional cluster analysis formed by the unweighted paired group mean analysis, and second, an analysis of the distribution of the “within-group” and “between-group” Dice coefficient. Clinical isolates from 114 cases of melioidosis occurring in the Northern Territory, Australia were studied; 71 strain types were defined with a Simpson’s index of 0.91. No correlation was found between strain type and disease severity or site of melioidosis on presentation, with no differences in similarity values found when comparing within and between-groups. In particular, isolates from patients with neurological melioidosis were not clustered. There was evidence of geographical localisation. This study suggests that the variation in strain type may not be as important as host and environmental factors in determining the pattern of disease.

Day/night pattern of arterial blood gases in the cow.

Both metabolic rate and pulmonary ventilation change throughout 24h with a circadian pattern. Because their changes occur almost in synchrony and by a similar amount, blood gases may remain steady within a narrow range. We tested this possibility in five cows (Bos taurus, Bruna Italiana breed), maintained in a stable at 29 degrees C, under natural light-dark (LD) regime, by measuring arterial blood gases every 3h for 2 days. All cows presented a clear day/night pattern of body temperature (T(b)), with an average peak-trough difference (PTD) of 0.5 degrees C. Breathing rate oscillated significantly in three out of five animals, with a group-mean PTD of 2 breaths per minute, and it was time-advanced with respect to the oscillation of T(b). Significant oscillations in arterial pH, bicarbonate, partial pressure of oxygen and partial pressure of carbon dioxide (Pa(CO2) ) were observed in, respectively, 1 cow out of 5, 1/5, 3/5 and 5/5. Of all these variables, group-mean analysis revealed a significant day/night pattern only for Pa(CO2), and even in this case the average PTD was less than 1 mmHg. We conclude that, in the cow, blood gases remain remarkably stable throughout the 24 h. Hence, the daily oscillations of body temperature, breathing rate, and probably of many other factors affecting metabolic rate and pulmonary ventilation do not preclude an excellent homeostasis of blood gases.

Metal-insulator transition, spin gap generation, and charge ordering in geometrically frustrated electron systems

We investigate a (semi-)metal to insulator transition (MIT) realized in geometrically frustrated electron systems on the basis of the Hubbard model on a three-dimensional pyrochlore lattice and a two-dimensional checkerboard lattice. Using the renormalization group method and mean field analysis, we show that in the half-filling case, MIT occurs as a result of the interplay between geometrical frustration and electron correlation. In the insulating phase, which has a spin gap, the spin rotational symmetry is not broken, while charge ordering exists. The charge ordered state is stabilized so as to relax the geometrical frustration in the spin degrees of freedom. We also discuss the distortion of the lattice structure caused by the charge ordering. The results are successfully applied to the description of the MIT observed in the pyrochlore system ${\rm Tl_2Ru_2O_7}$.

Geometrical-frustration-induced (Semi)metal-to-insulator transition.

We study the low-energy properties of the geometrically frustrated Hubbard model on a three-dimensional pyrochlore lattice and a two-dimensional checkerboard lattice on the basis of the renormalization group method and mean field analysis. It is found that, in the half-filling case, a (semi)metal to insulator transition (MIT) occurs. Also, in the insulating phase, which has a spin gap, the spin rotational symmetry is not broken, while charge ordering exists. The results are applied to the description of the MIT observed in the pyrochlore system Tl2Ru2O7.

Serial passage of foot-and-mouth disease virus in sheep reveals declining levels of viraemia over time.

If an infectious agent is to maintain itself within a closed population by means of an unbroken serial chain of infections, it must maintain the level of infectiousness of individuals through time, or termination of the transmission chain is inevitable. One possible cause of diminution in infectiousness along serial chains of transmission may be that individuals are unable to amplify and transmit comparable levels of the infectious agent. Here, the results are reported of a novel experiment designed specifically to assess the effects of serial passage of foot-and-mouth disease virus (FMDV) in experimental groups of sheep. A virus isolate taken from an epidemic of foot-and-mouth disease (FMD) characterized by rapid fade-out of infection was passed serially through four groups of sheep housed in an isolation unit. Although it was not possible to measure individual infectiousness directly, blood virus load from infected individuals was quantified using a real-time PCR assay and used as an underlying indicator of the level of infection. The results of this assay concurred well with those of the traditional tissue-culture assay and were shown to be highly repeatable. The level of peak viraemia was shown to fall significantly with the time of infection and with passage group, both in terms of the group mean and regression analysis of individual values, suggesting that this isolate of FMDV may, under certain conditions, be unable to maintain itself indefinitely in susceptible sheep populations. The results of these experiments are discussed in terms of the epidemiology of FMD in sheep.