Abstract
A large pertussis epidemic occurred between 2008 and 2010 in Japan. To investigate epidemic strains, we analyzed 33 Bordetella pertussis isolates from the epidemic period by sequencing virulence-associated genes (fim3, ptxP, ptxA, and prn) and performing multilocus variable-number tandem repeat analysis (MLVA), and compared these results with those of 101 isolates from non-epidemic, earlier and later time periods. DNA sequencing of the fim3 allele revealed that the frequency of fim3B was 4.3%, 12.8%, 30.3%, and 5.1% within isolates in 2002–2004, 2005–2007, 2008–2010, and 2011–2012, respectively. The isolation rate of the fim3B strain therefore temporarily increased during the epidemic period 2008–2010. In contrast, the frequencies of the virulence-associated allelic variants, ptxP3, ptxA1, and prn2, increased with time during overall study period, indicating that these variants were not directly involved in the occurrence of the 2008–2010 epidemic. MLVA genotyping in combination with analysis of allele types showed that the prevalence of an MT27d strain temporarily increased in the epidemic period, and that this strain carried virulence-associated allelic variants (fim3B, ptxP3, ptxA1, and prn2) also identified in recent epidemic strains of Australia, Europe, and the US. Phenotypic analyses revealed that the serotype Fim3 strain was predominant (≥87%) during all the periods studied, and that the frequency of adhesion pertactin (Prn) non-expressing B. pertussis decreased by half in the epidemic period. All MT27d strains expressed Prn and Fim3 proteins, suggesting that B. pertussis MT27d strains expressing Prn and Fim3B have the potential to cause large epidemics worldwide.
Highlights
Bordetella pertussis, a highly communicable Gram-negative coccobacillus, is the cause of pertussis, a major acute respiratory infection resulting in severe childhood illness and infant death [1]
The number of pertussis patients over 15 years of age steadily increased in the 2000s, alongside increases of adolescent and adult incidence rates (40.7%, 44.2%, and 52.9% of all reported cases in 2008, 2009, and 2010, respectively), in 2011, the number of those patients decreased and the incidence rate in adolescents and adults decreased to 41%
We demonstrated that the prevalence of B. pertussis strains carrying fim3B, which were classified as MT27d, temporarily increased during the 2008–2010 pertussis epidemic in
Summary
Bordetella pertussis, a highly communicable Gram-negative coccobacillus, is the cause of pertussis (whooping cough), a major acute respiratory infection resulting in severe childhood illness and infant death [1]. In Japan, acellular pertussis vaccines (ACVs) were introduced in 1981 and are used to control pertussis with a schedule of 3 primary doses and single booster dose at ages 3, 4, 6, and 18223 months, respectively. This vaccination schedule has been followed since 1994. The waning of vaccine-acquired immunity and the decrease in opportunities of natural immune boosting owing to reduced levels of B. pertussis circulation have been proposed as explanations for the recent resurgences of pertussis [2,8,9]. Another possible underlying factor is the adaptation of the B. pertussis population to vaccine-induced immunity [2,10,11]
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