Raymond S. W. Tsang

Global Population Structure and Evolution of Bordetella pertussis and Their Relationship with Vaccination

ABSTRACT Bordetella pertussis causes pertussis, a respiratory disease that is most severe for infants. Vaccination was introduced in the 1950s, and in recent years, a resurgence of disease was observed worldwide, with significant mortality in infants. Possible causes for this include the switch from whole-cell vaccines (WCVs) to less effective acellular vaccines (ACVs), waning immunity, and pathogen adaptation. Pathogen adaptation is suggested by antigenic divergence between vaccine strains and circulating strains and by the emergence of strains with increased pertussis toxin production. We applied comparative genomics to a worldwide collection of 343 B. pertussis strains isolated between 1920 and 2010. The global phylogeny showed two deep branches; the largest of these contained 98% of all strains, and its expansion correlated temporally with the first descriptions of pertussis outbreaks in Europe in the 16th century. We found little evidence of recent geographical clustering of the strains within this lineage, suggesting rapid strain flow between countries. We observed that changes in genes encoding proteins implicated in protective immunity that are included in ACVs occurred after the introduction of WCVs but before the switch to ACVs. Furthermore, our analyses consistently suggested that virulence-associated genes and genes coding for surface-exposed proteins were involved in adaptation. However, many of the putative adaptive loci identified have a physiological role, and further studies of these loci may reveal less obvious ways in which B. pertussis and the host interact. This work provides insight into ways in which pathogens may adapt to vaccination and suggests ways to improve pertussis vaccines. IMPORTANCE Whooping cough is mainly caused by Bordetella pertussis, and current vaccines are targeted against this organism. Recently, there have been increasing outbreaks of whooping cough, even where vaccine coverage is high. Analysis of the genomes of 343 B. pertussis isolates from around the world over the last 100 years suggests that the organism has emerged within the last 500 years, consistent with historical records. We show that global transmission of new strains is very rapid and that the worldwide population of B. pertussis is evolving in response to vaccine introduction, potentially enabling vaccine escape. Whooping cough is mainly caused by Bordetella pertussis, and current vaccines are targeted against this organism. Recently, there have been increasing outbreaks of whooping cough, even where vaccine coverage is high. Analysis of the genomes of 343 B. pertussis isolates from around the world over the last 100 years suggests that the organism has emerged within the last 500 years, consistent with historical records. We show that global transmission of new strains is very rapid and that the worldwide population of B. pertussis is evolving in response to vaccine introduction, potentially enabling vaccine escape.

Genomic resolution of an aggressive, widespread, diverse and expanding meningococcal serogroup B, C and W lineage.

Summary Objectives Neisseria meningitidis is a leading cause of meningitis and septicaemia. The hyperinvasive ST-11 clonal complex (cc11) caused serogroup C (MenC) outbreaks in the US military in the 1960s and UK universities in the 1990s, a global Hajj-associated serogroup W (MenW) outbreak in 2000–2001, and subsequent MenW epidemics in sub-Saharan Africa. More recently, endemic MenW disease has expanded in South Africa, South America and the UK, and MenC cases have been reported among European and North American men who have sex with men (MSM). Routine typing schemes poorly resolve cc11 so we established the population structure at genomic resolution. Methods Representatives of these episodes and other geo-temporally diverse cc11 meningococci (n = 750) were compared across 1546 core genes and visualised on phylogenetic networks. Results MenW isolates were confined to a distal portion of one of two main lineages with MenB and MenC isolates interspersed elsewhere. An expanding South American/UK MenW strain was distinct from the ‘Hajj outbreak’ strain and a closely related endemic South African strain. Recent MenC isolates from MSM in France and the UK were closely related but distinct. Conclusions High resolution ‘genomic’ multilocus sequence typing is necessary to resolve and monitor the spread of diverse cc11 lineages globally.

Characterization of Invasive Haemophilus influenzae Disease in Manitoba, Canada, 2000–2006: Invasive Disease due to Non-Type B Strains

In addition to the proportional increase in cases of non-type b Haemophilus influenzae disease in the post-H. influenzae type b vaccine era, the incidence of invasive H. influenzae disease was found to be approaching the rates of H. influenzae type b disease that were documented in the prevaccine period. Fifty-six percent of invasive disease now occurs in individuals aged >10 years.

Epidemiology of Haemophilus influenzae serotype a, North American Arctic, 2000-2005.

Serotype a is now the most common seen in the North American Arctic; highest rates occur in indigenous children.

Macrolide Resistance and Molecular Types of Treponema pallidum Causing Primary Syphilis in Shanghai, China

BACKGROUND The resurgence of syphilis in China requires laboratories to update their methods for molecular epidemiology investigation and surveillance. This study focuses on implementing polymerase chain reaction (PCR) diagnostic tests for syphilis and for detection of molecular subtypes and macrolide resistance among strains causing primary syphilis in the city of Shanghai, China. METHODS Swabs were obtained from the genital lesions of 39 patients who presented with symptoms compatible with primary syphilis. Eight of the patients also provided whole blood samples. Swabs were also obtained from 10 patients without syphilis who presented with genital ulcers. PCR tests to amplify 3 common but unlinked treponemal genes were performed on DNA samples extracted from these specimens. Molecular subtyping was based on genetic characterization of 2 treponemal repeat genes, arp and tpr. Detection of macrolide resistance was accomplished by identification of the 23S ribosomal RNA gene mutation associated with the resistance pattern. RESULTS Thirty-eight patients with primary syphilis were found to have Treponema pallidum DNA in their genital lesions by PCR assays using primers that target the bmp, tpp-47, and polA genes. None of the patients without syphilis had positive PCR results. Five molecular subtypes were identified, with 1 type (14f) causing 79% of the cases. All 38 patients were found to be infected with macrolide-resistant strains. CONCLUSIONS Three common treponemal gene targets (bmp, tpp-47, and polA) were detectable by PCR in patients with primary syphilis. A single clone characterized as 14f and showing macrolide resistance appeared to have caused most of the primary syphilis cases in this study.

Diversity of Canadian meningococcal serogroup B isolates and estimated coverage by an investigational meningococcal serogroup B vaccine (4CMenB).

BACKGROUND In collaboration with the Canadian Immunization Monitoring Program Active (IMPACT), the National Microbiology Laboratory, the UK Health Protection Agency and Novartis Vaccines, we tested the potential of an investigational 4-component meningococcal B vaccine (4CMenB) to cover Canadian strains circulating from 2006 to 2009. METHODS IMPACT meningococcal surveillance is population based and includes over 50% of Canadian adults and children. All isolates were characterized by Meningococcal Antigen Typing System (MATS) and sequencing for factor H-binding protein (fHbp), Neisseria Heparin Binding Antigen (NHBA) and Neisserial adhesin A (NadA). RESULTS In total, 157 isolates were tested. Overall, 4CMenB MATS predicted strain coverage was 66% (95% CI: 46-78%), with 26%, 29% and 11% of strains covered by one, two and three vaccine antigens, respectively. The coverage of each antigen was as follows: 13% PorA, 1% NadA, 52% fHbp and 51% NHBA. The majority of strains for clonal complex (cc) 41/44 and cc60 were covered by NHBA; the majority of strains for cc269 and cc32 were covered by fHbp and NHBA. Coverage for two prevalent strains (sequence type (ST)-269 and ST-154) was 95% and 100%, respectively. CONCLUSIONS 4CMenB has the potential to protect against a significant proportion of Canadian invasive MenB strains.

Polymorphisms of the Fimbria fim3 Gene of Bordetella pertussis Strains Isolated in Canada

ABSTRACT The fim genes which code for the fimbria protective antigens present in both the inactivated whole-cell and acellular vaccines were analyzed in 86 Canadian Bordetella pertussis isolates. At least one of the novel mutations identified was found to involve a surface epitope that has been mapped by serum antibodies from infected or vaccinated subjects.

Molecular Characterization of Syphilis in Patients in Canada: Azithromycin Resistance and Detection of Treponema pallidum DNA in Whole-Blood Samples versus Ulcerative Swabs

ABSTRACT Although detection of Treponema pallidum DNA in whole-blood specimens of syphilis patients has been reported, it is uncertain at what stage of the disease such specimens are most suitable for the molecular diagnosis of syphilis. Also, few studies have directly compared the different gene targets for routine laboratory diagnostic usage in PCR assays. We examined 87 specimens from 68 patients attending two urban sexually transmitted disease clinics in Alberta, Canada. PCR was used to amplify the T. pallidum tpp47, bmp, and polA genes as well as a specific region of the 23S rRNA gene linked to macrolide antibiotic susceptibility. In primary syphilis cases, PCR was positive exclusively (75% sensitivity rate) in ulcerative swabs but not in blood specimens, while in secondary syphilis cases, 50% of the blood specimens were positive by PCR. Four out of 14 (28.6%) of our PCR-positive syphilis cases were found to be caused by an azithromycin-resistant strain(s). Our results confirmed that swabs from primary ulcers are the specimens of choice for laboratory diagnostic purposes. However, further research is required to determine what specimen(s) would be most appropriate for molecular investigation of syphilis in secondary and latent syphilis.

The impact of childhood meningococcal serogroup C conjugate vaccine programs in Canada.

Background: Conjugate meningococcal vaccines may decrease the incidence of disease. The staggered implementation of universal childhood meningococcal C conjugate (MenC) immunization programs across Canada offers an opportunity to evaluate the influence of these programs. Methods: From 2002 to 2006, we conducted active, population-based surveillance for adult and pediatric hospital admissions related to meningococcal infections at the 12 centers of the Canadian Immunization Monitoring Program, Active (IMPACT), in collaboration with local public health officials. Results: A total of 376 cases were reported during the 5 years of surveillance. Yearly totals were as follows: 96 in 2002, 73 in 2003, 81 in 2004, 58 in 2005, and 68 in 2006. Case fatality was 9.3% and adults had a significantly higher case fatality rate than children. Average incidence per 100,000 was 0.62 (95% confidence interval [CI]: 0.50–0.76) in 2002 and 0.42 (95% CI: 0.32–0.53) in 2006. The highest rates were in children age 0 to 4 years, followed by adolescents age 15 to 19 years. Incidence of group C disease decreased significantly during the 5 years from 0.23 (95% CI: 0.16–0.32) in 2002 to 0.08 (95% CI: 0.04–0.14) in 2006, whereas incidence remained stable for groups B, Y, and W135. The decrease in group C disease was seen in provinces that first implemented MenC immunization programs. Conclusions: A substantial decrease in group C incidence occurred in provinces with early MenC immunization programs. Serogroup C incidence remained stable in provinces without MenC programs. We found no evidence of serogroup replacement.

Invasive Haemophilus influenzae disease: changing epidemiology and host-parasite interactions in the 21st century.

Introduction of Haemophilus influenzae type b (Hib) conjugate vaccines in late 1980s-early 1990s made a dramatic effect on the incidence of invasive Hib disease among children in many industrialized countries with routine Hib immunization programs. However, cases of vaccine failure and an increased susceptibility to invasive Hib as well as non-type b H. influenzae disease have been consistently reported among individuals with various congenital and acquired immunodeficiencies. Remarkably, in the 21st century, diseases due to non-type b strains of H. influenzae are becoming relatively more frequent than before. Despite the overall successful immunization against Hib, some indigenous populations, i.e. Australian Aboriginal and North American Indian children still experience increased rates of invasive H. influenzae disease. In order to monitor the evolving nature of invasive H. influenzae disease, carefully documented surveillance data is required to capture the true magnitude of the problem. Developing new vaccines against non-type b H. influenzae is a potential solution to protect some vulnerable populations against the invasive disease.