Bordetella pertussis isolates in Argentina: genetic divergence with vaccine strain

HOZBOR D.; BOTTERO D.; G. WELTMAN,; GAILLARD ME.; A. GRAIEB; FERNÁNDEZ J.; B. GATTI; REGUEIRA M; BINSZTEIN N.

Atlanta Georgia, USA.

Conferencia; International Conference on Emerging Infectious Diseases 2006; 2006

CDC

Background: In Argentina, as in other countries, the number of whooping cough cases has been increasing, even in highly vaccinated zones. Many reports suggest that the decline of vaccine efficacy due to antigenic shifts in the circulating Bordetella pertussis might be among the factors that contribute to pertussis reemergence in different parts of the world. To evaluate the incidence of this factor in Argentina, we decided to characterize the circulating Bordetella of an important demographic area of this country in comparison with a strain used for vaccine production.Methods: From 2000 to 2004 we collected nasopharyngeal samples from 569 pediatric patients with signs of Bordetella infection hospitalized mainly in the metropolitan area of Buenos Aires and La Plata, Argentina. From these samples we identified 46 B. pertussis, which were characterized by biochemical tests, PCR, PFGE typing, prn and ptx genes sequencing.Results: The relatedness for the DNA PFGE profiles obtained after XbaI restriction were calculated by UPGMA clustering of Dice coefficients, using the BioNumerics software. The analysis clearly discriminated three major PFGE profiles groups: I–II-III. The Argentinean clinical isolates were clustered in two groups, II and III (á, â). The level of relatedness was 79,5% for group II, 81,8% for group III á and 85% for group III â. The profiles corresponding to the vaccine strain Tohama I (group I á) and the WHO reference strain 18323 (group I â) had a much lower similarity with all Argentinean isolates with relatedness of 66 %. Differences between Argentinean circulating B. pertussis and the vaccine strain were also observed for the prn and ptx genes. In addition, we identified four B. bronchiseptica.Conclusions: The observed genetic differences between circulating B. pertussis strains and the one commonly used in vaccine production should be considered for the development of an improved local vaccine.