Whooping cough continues to lead in the group of vaccine-controlled infectious diseases, despite the mass immunization carried out all over the world. In recent decades there has been a significant increase in the incidence of whooping cough, the spread of atypical forms among adolescents and adults.
Suspectedly the formation of source of anthroponosis occurs due to B. pertussis bacteria with reduced or completely lost virulence, capable of long-term persistence in the human body and restoration of infectivity under certain conditions. The mechanisms of persistence of the causative agent of whooping cough have not yet been studied completely. We suppose that one of the mechanisms may be a change of the bvgAS operon, which regulates the expression of all virulence genes of B. pertussis bacteria because of the integration of IS-elements. Mobile IS-elements are known to have the ability to both embed into the host genome sites and be cut out of them with the restoration of impaired functions.
THE PURPOSE OF THIS STUDY
is to evaluate the duration of persistence and to analyze the composition of populations of B. pertussis bacteria in children with pertussis and contact persons in family foci.
MATERIAL AND METHODS
80 children with pertussis and 116 persons from 59 family foci of pertussis were examined in contact with these children. Patients were included in the study after they signed an informed consent. To detect B. pertussis DNA in nasopharyngeal swabs and to register IS-element integrations, the PCR-RT-IS test-system developed at the N.F. Gamalei Research Institute, nested PCR, sequencing were used.
RESULTS
The possibility of long-term detection of the causative agent of whooping cough in patients at different stages of the disease and in family members who have been in contact with patients is shown. It was found that in the period of convalescence of whooping cough in 25% of patients, the formation of insertional avirulent mutants of B. pertussis in the upper respiratory tract, capable of long-term persistence in the human body, is observed. With a lower frequency (15%) the formation of avirulent mutants was registered in contact persons in family foci.
CONCLUSION
The long-term detection of the causative agent of whooping cough and the registration of B. pertussis bvg-mutants containing the integration of IS-elements in bacterial carriers confirm the hypothesis of the possibility of the transition of bacteria to persistence because of the insertion inactivation of the bvgAS operon. Identifying persistent B. pertussis bacteria and studying the mechanisms of their formation is important for creating new vaccination strategies and improvement of pertussis vaccines.
