Evolution of Bordetella pertussis

Bordetella pertussis: An agent not to be forgotten in Qatar

BACKGROUND

Pertussis (whooping cough) is a vaccine-preventable disease caused by the bacterium Bordetella pertussis that is spread by airborne respiratory droplets. Clinical symptoms vary from infants to adults and are most contagious before the onset of symptoms. Infants are at the highest risk of infection, especially before they are old enough to receive at least two doses of pertussis-containing vaccine. There have been no indigenous cases of pertussis in Qatar since 2010 until 2018, due to free pertussis-containing vaccines under the National Immunization Schedule of Qatar, with coverage consistently above 95%. Two cases were reported in 2016 but were found to be imported. In 2019, 20 infants were reported as suspected pertussis to the Health Promotion and Communicable Disease Control (HP-CDC), Ministry of Public Health (MOPH), Qatar; of them, five were laboratory confirmed as pertussis.

OBJECTIVE

This study aimed to describe the five confirmed cases of pertussis reported to HP-CDC, MOPH, Qatar, between January 1 and December 30, 2019. Summary of Cases: All five confirmed pertussis cases were under one year old, and three were boys. All except one were immunized-for-age, and three had not received any doses of pertussis-containing vaccine and in none of the cases had the mother received tetanus, diphtheria, and acellular pertussis (Tdap) vaccine during pregnancy. All infants were born in Qatar, and two were Qatari nationals.

CONCLUSION

There may be a possibility of re-emergence of pertussis in Qatar. Active immunization and coverage maintenance are the best tools to prevent re-emergence. Undiagnosed and untreated pertussis cases are potential sources of infection. The partial or unimmunized groups may be significantly at risk, especially during infancy and before reaching the age to complete the three primary doses of diphtheria, tetanus, and pertussis vaccines. Focus on increasing awareness among those providing antenatal care, regarding the importance of Tdap vaccination during pregnancy, is necessary.

What Is Wrong with Pertussis Vaccine Immunity? The Problem of Waning Effectiveness of Pertussis Vaccines

Pertussis is resurgent in some countries, particularly those in which children receive acellular pertussis (aP) vaccines in early infancy and boosters later in life. Immunologic studies show that, whereas whole-cell pertussis (wP) vaccines orient the immune system toward Th1/Th17 responses, acellular pertussis vaccines orient toward Th1/Th2 responses. Although aP vaccines do provide protection during the first years of life, the change in T-cell priming results in waning effectiveness of aP as early as 2-3 years post-boosters. Although other factors, such as increased virulence of pertussis strains, better diagnosis, and better surveillance may play a role, the increase in pertussis appears to be the result of waning immunity. In addition, studies in baboon models, requiring confirmation in humans, show that aP is less able to prevent nasopharyngeal colonization of Bordetella pertussis than wP or natural infection.

Multi-locus variable-number tandem repeat analysis of Bordetella pertussis isolates circulating in Poland in the period 1959-2013

PURPOSE

Despite the long history of pertussis vaccination and high vaccination coverage in Poland and many other developed countries, pertussis incidence rates have increased substantially, making whooping cough one of the most prevalent vaccine-preventable diseases. Among the factors potentially involved in pertussis resurgence, the adaptation of the Bordetella pertussis population to country-specific vaccine-induced immunity through selection of non-vaccine-type strains still needs detailed studies.

METHODOLOGY

Multi-locus variable-number tandem repeat analysis (MLVA), also linked to MLST and PFGE profiling, was applied to trace the genetic changes in the B. pertussis population circulating in Poland in the period 1959-2013 versus country-specific vaccine strains.

RESULTS

Generally, among 174 B. pertussis isolates, 31 MLVA types were detected, of which 11 were not described previously. The predominant MLVA types of recent isolates in Poland were different from those of the typical isolates circulating in other European countries. The MT27 type, currently predominant in Europe, was rarely seen and detected in only five isolates among all studied. The features of the vaccine strains used for production of the pertussis component of a national whole-cell diphtheria-tetanus-pertussis (DTP) vaccine, as studied by MLVA and MLST tools, were found to not match those observed in the currently circulating B. pertussis isolates in Poland.

CONCLUSIONS

Differences traced by MLVA in relation to the MLST and PFGE profiling confirmed that the B. pertussis strain types currently observed elsewhere in Europe, even if appearing in Poland, were not able to successfully disseminate within a human population in Poland that has been vaccinated with a whole-cell pertussis vaccine not used in other countries.