Thermal-Stress and Low-Cycle Fatigue Data on Typical Materials

This paper presents the results of low-cycle-fatigue tests wherein either thermal strain or mechanical strain was the independent variable. The materials investigated were primarily ferrous alloys for use in nuclear reactors. The analysis of results was based on plastic-strain-range measurements which could be made reproducibly in the 2 x 10 -5 range. Graphs of plastic strain range versus cycles to failure were often found to be independent of large variations in temperature and cycle time. The results from thermal-fatigue and constant-temperature-fatigue tests were usually indistinguishable on these graphs, suggesting that identical metallurgical phenomena occurred in each type of test

SNP-Based Typing: A Useful Tool to Study Bordetella pertussis Populations

To monitor changes in Bordetella pertussis populations, mainly two typing methods are used; Pulsed-Field Gel Electrophoresis (PFGE) and Multiple-Locus Variable-Number Tandem Repeat Analysis (MLVA). In this study, a single nucleotide polymorphism (SNP) typing method, based on 87 SNPs, was developed and compared with PFGE and MLVA. The discriminatory indices of SNP typing, PFGE and MLVA were found to be 0.85, 0.95 and 0.83, respectively. Phylogenetic analysis, using SNP typing as Gold Standard, revealed false homoplasies in the PFGE and MLVA trees. Further, in contrast to the SNP-based tree, the PFGE- and MLVA-based trees did not reveal a positive correlation between root-to-tip distance and the isolation year of strains. Thus PFGE and MLVA do not allow an estimation of the relative age of the selected strains. In conclusion, SNP typing was found to be phylogenetically more informative than PFGE and more discriminative than MLVA. Further, in contrast to PFGE, it is readily standardized allowing interlaboratory comparisons. We applied SNP typing to study strains with a novel allele for the pertussis toxin promoter, ptxP3, which have a worldwide distribution and which have replaced the resident ptxP1 strains in the last 20 years. Previously, we showed that ptxP3 strains showed increased pertussis toxin expression and that their emergence was associated with increased notification in the Netherlands. SNP typing showed that the ptxP3 strains isolated in the Americas, Asia, Australia and Europe formed a monophyletic branch which recently diverged from ptxP1 strains. Two predominant ptxP3 SNP types were identified which spread worldwide. The widespread use of SNP typing will enhance our understanding of the evolution and global epidemiology of B. pertussis

Increased Population Prevalence of Low Pertussis Toxin Antibody Levels in Young Children Preceding a Record Pertussis Epidemic in Australia

Background: Cross-sectional serosurveys using IgG antibody to pertussis toxin (IgG-PT) are increasingly being used to estimate trends in recent infection independent of reporting biases. Methods/Principal Findings: We compared the age-specific seroprevalence of various levels of IgG-PT in cross-sectional surveys using systematic collections of residual sera from Australian diagnostic laboratories in 1997/8, 2002 and 2007 with reference to both changes in the pertussis vaccine schedule and the epidemic cycle, as measured by disease notifications. A progressive decline in high-level ($62.5 EU/ml) IgG-PT prevalence from 19 % (95 % CI 16–22%) in 1997/98 to 12 % (95 % CI 11–14%) in 2002 and 5 % (95 % CI 4–6%) in 2007 was consistent with patterns of pertussis notifications in the year prior to each collection. Concomitantly, the overall prevalence of undetectable (,5 EU/ml) levels increased from 17 % (95 % CI 14– 20%) in 1997/98 to 38 % (95 % CI 36–40%) in 2007 but among children aged 1–4 years, from 25 % (95 % CI 17–34%) in 1997/98 to 62 % (95 % CI 56–68%) in 2007. This change followed withdrawal of the 18-month booster dose in 2003 and preceded record pertussis notifications from 2008 onwards. Conclusions/Significance: Population seroprevalence of high levels of IgG-PT is accepted as a reliable indicator of pertussis disease activity over time within and between countries with varying diagnostic practices, especially in unimmunised age groups. Our novel findings suggest that increased prevalence of undetectable IgG-PT is an indicator of waning immunit

Evidence of Bordetella pertussis infection in vaccinated 1-year-old Danish children

We measured IgA and IgG antibodies to pertussis toxin (PT) and filamentous hemagglutinin (FHA) in sera from 203 1-year-old children who had received one to three doses of a monocomponent PT toxoid vaccine. Ten children (5%) had IgA antibody to PT indicating recent infection; seven of these children had received three doses of vaccine. PT IgA responders did not have significantly longer coughing episodes than PT IgA non-responders. Since an IgA antibody response occurs in only ∼50% of infected children, the actual infection rate in our cohort is estimated to ∼10%. The apparent high Bordetella pertussis infection rate in Danish infants suggests that the monocomponent PT toxoid vaccine used in Denmark has limited efficacy against B. pertussis infection. A prospective immunization study comparing a multi-component vaccine with the present monocomponent PT toxoid vaccine should be undertaken

Clinical presentation of pertussis in fully immunized children in Lithuania

BACKGROUND: In Lithuania, the vaccination coverage against pertussis is high. Nevertheless, there is a significant increase in pertussis cases in fully immunized children. The aim of our study was to determine the frequency of classical symptoms of laboratory confirmed pertussis and describe its epidemiology in children fully vaccinated against pertussis. METHODS: From May to December 2001, 70 children aged 1 month to 15 years, suffering from prolonged cough were investigated in the Centre of Paediatrics, Vilnius University Children's Hospital. The collected information included personal data, vaccination history, clinical symptoms of the current illness, and treatment before hospitalization. At the admission to the hospital blood samples were taken from all studied children for Bordetella pertussis IgM and IgA. RESULTS: A total of 53 (75.7%) of the 70 recruited patients with prolonged cough showed laboratory evidence of pertussis. 32 of them were fully vaccinated with whole cell pertussis vaccine (DTP). The age of fully vaccinated patients varied from 4 to 15 years (average 10.9 ± 3.1; median 11). The time period between the last vaccination dose (fourth) and the clinical manifestation of pertussis was 2.6–13 years (average 8.9 ± 3.0; median 9). More than half of the children before the beginning of pertussis were in contact with persons suffering from long lasting cough illness in the family, school or day-care center. The mean duration from onset of pertussis symptoms until hospitalization was 61.4 ± 68.3 days (range, 7 to 270 days; median 30). For 11 patients who had had two episodes (waves) of coughing, the median duration of cough was 90 days, and for 21 with one episode 30 days (p < 0.0002). Most of the children (84.4%) had paroxysmal cough, 31.3% had post-tussive vomiting, 28.1% typical whoop, and 3.1% apnea. Only 15.6% children had atypical symptoms of pertussis. CONCLUSION: Fully vaccinated children fell ill with pertussis at the median of 11 years old, 9 years following pertussis vaccination. More than half of the children could catch pertussis at home, at school or day-care center. Clinical picture of pertussis in previously immunized children is usually characterized by such classical symptoms as prolonged and paroxysmal cough, rarely by whopping and post-tussive vomiting, and very rarely by apnea

Bordetella pertussis Strains with Increased Toxin Production Associated with Pertussis Resurgence

A more virulent strain of the disease is emerging

Immune Boosting Explains Regime-Shifts in Prevaccine-Era Pertussis Dynamics

Understanding the biological mechanisms underlying episodic outbreaks of infectious diseases is one of mathematical epidemiology’s major goals. Historic records are an invaluable source of information in this enterprise. Pertussis (whooping cough) is a re-emerging infection whose intermittent bouts of large multiannual epidemics interspersed between periods of smaller-amplitude cycles remain an enigma. It has been suggested that recent increases in pertussis incidence and shifts in the age-distribution of cases may be due to diminished natural immune boosting. Here we show that a model that incorporates this mechanism can account for a unique set of pre-vaccine-era data from Copenhagen. Under this model, immune boosting induces transient bursts of large amplitude outbreaks. In the face of mass vaccination, the boosting model predicts larger and more frequent outbreaks than do models with permanent or passively-waning immunity. Our results emphasize the importance of understanding the mechanisms responsible for maintaining immune memory fo

Comparative Genomics of Bordetella pertussis Reveals Progressive Gene Loss in Finnish Strains

BACKGROUND: Bordetella pertussis is a gram-negative bacterium that infects the human respiratory tract and causes pertussis or whooping cough. The disease has resurged in many countries including Finland where the whole-cell pertussis vaccine has been used for more than 50 years. Antigenic divergence has been observed between vaccine strains and clinical isolates in Finland. To better understand genome evolution in B. pertussis circulating in the immunized population, we developed an oligonucleotide-based microarray for comparative genomic analysis of Finnish strains isolated during the period of 50 years. METHODOLOGY/PRINCIPAL FINDINGS: The microarray consisted of 3,582 oligonucleotides (70-mer) and covered 94% of 3,816 ORFs of Tohama I, the strain of which the genome has been sequenced. Twenty isolates from 1953 to 2004 were studied together with two Finnish vaccine strains and two international reference strains. The isolates were selected according to their characteristics, e.g. the year and place of isolation and pulsed-field gel electrophoresis profiles. Genomic DNA of the tested strains, along with reference DNA of Tohama I strain, was labelled and hybridized. The absence of genes as established with microarrays, was confirmed by PCR. Compared with the Tohama I strain, Finnish isolates lost 7 (8.6 kb) to 49 (55.3 kb) genes, clustered in one to four distinct loci. The number of lost genes increased with time, and one third of lost genes had functions related to inorganic ion transport and metabolism, or energy production and conversion. All four loci of lost genes were flanked by the insertion sequence element IS481. CONCLUSION/SIGNIFICANCE: Our results showed that the progressive gene loss occurred in Finnish B. pertussis strains isolated during a period of 50 years and confirmed that B. pertussis is dynamic and is continuously evolving, suggesting that the bacterium may use gene loss as one strategy to adapt to highly immunized populations