Comparative genomics of Whooping cough vaccine strains from India

-By Kranti Karande

File:Bordetella pertussis on Charcoal Agar supplemented with ...

Pertussis also known as Whooping cough is a highly contagious respiratory disease, endemic in all countries. It is caused by the bacterium Bordetella pertussis that survives in mouth, nose and throat region. Pertussis is known for uncontrollable, frequent coughing and breathing difficulties, a disease found most dangerous in infants.

The aim of pertussis vaccination is to reduce risk of severe disease in infants and young children. There are two types of pertussis vaccines: whole-cell vaccines based on killed B.pertussis organisms and acellular pertussis dependent on one or more highly purified pertussis antigens. Despite high vaccine coverage, re-emergence of pertussis is observed globally. There are different factors contributing for this disease resurgence. Genetic divergence in the circulating strains of B.pertussis has been reported as one of the important contributing factors for the same.

Our current knowledge of the genetic evolution of B.pertussis in circulating strains is largely focused on studies carried out in countries using ACVs (Acellular Vaccines) targeting only a few antigens used in the production of ACVs. In order to better understand adaptation to vaccine-induced selection pressure, it will be essential to study B.pertussis populations in developing countries where WCVs (Whole-Cell Vaccines) are used. India is a significant user and global supplier of WCVs.

This article briefly describes a study conducted by researchers to compare genomes of B.pertussis vaccine strains and clinical isolates reported from India. Genetic divergence was mostly studied in circulating strains of B. pertussis concerning vaccine antigens such as pertussis toxin, pertactin, fimbriae and filamentous hemaglutinnin. Whole genome sequences obtained from five different vaccine strains were compared with reference strain (Tohama-I) and two recently isolated clinical isolates from India. Core-genome based phylogenetic analysis was also performed using isolates reported from countries using ACV.

Whole-genome analysis of vaccines and clinical isolates reported from India revealed high genetic similarity and conserved genome among strains. Phylognetic analysis showed that clinical and vaccine strains share genetic closeness with reference strain.

This study provides detailed characterization of vaccine and clinical strains reported from India, which will further facilitate epidemiological studies on genetic shifts in countries which are using WCVs in their immunization program.


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