Whooping cough: the mechanisms used by the bacterium to survive are described
CONICET investigators discovered the way in which this microorganism can avoid the immune system and linger in the body
María Eugenia Rodríguez and her work team. [Photo: courtesy of investigators]
Whooping cough, brought about by the bacterium named Bordetella pertussis, is a significant cause of morbidity and infant mortality. According to the information provided by Organización Mundial de la Salud (World Health Organization, WHO), there are approximately 50 million cases per year and 300 thousand deaths worldwide.
In a research published on Pathogens and Disease magazine, National Council of Scientific and Technical Research (CONICET) scientists at Centro de Investigación y Desarrollo en Fermentaciones Industriales (CINDEFI, CONICET-UNLP) demonstrated how this microorganism avoids the immune system.
In 2010, this team demonstrated that Bordetella pertussis survives within human macrophages, one of the immune system cell types which fights the bacterium. In this study, the mechanisms used by Bordetella pertussis to inhabit and even replicate in the interior of macrophages is described. This would indicate that these cells may act as niche for its preservation.
“We have discovered that this bacterium, when there are no opsonic antibodies [that is to say, those that ‘mark’ the pathogen for its destruction,] enters the macrophage and lingers in the gallbladders, early endosomes, and from that point, it may proliferate, infect the macrophage and create a persistence niche,” explained María Eugenia Rodríguez, the main investigator of CONICET at CINDEFI and one of the research authors.
This is accomplished thanks to two bacterial toxins, Ptx y CyaA, which produce the response of macrophagic genes to prevent them from acting and survive in the interior. “Through these two toxins, all that should be killed by it is inhibited, all inflammatory response and germicide reaction,” adds Rodríguez.
This finding enables us to understand how these bacteria linger in adult populations without causing any symptoms. “Thus, the bacterium lingers in a latent state inside the macrophages, and the other cells of the immune system cannot "perceive" it as being infected because Bordetella pertussis regulates all mechanisms that would make it detectable. This is called an inapparent carrier, and it explains why this bacterium has lingered for decades in populations which have been vaccinated and in adults who do not cough,” concludes Rodríguez.
Whooping cough in Argentina
Data of the Ministerio de Salud de la Nación (Ministry of Health of Argentina) reveal that in 2011 there were 1,594 confirmed cases and 70 death cases of children under 1 year old. Out of the confirmed cases, 91 percent were babies under 4 months of age. In 2012, 568 confirmed cases of whooping cough with Bordetella pertussis were reported. Nowadays, the vaccine is the only method available for prevention. The Calendario Nacional de Vacunación (National Vaccination Schedule) includes four vaccines which provide immunity against whooping cough: pentavalent, applied when the baby is 2, 4 and 6 months of age; quadruple, applied when the baby is 18 months of age; tetanus, diphtheria and cellular pertussis vaccine, applied when the child starts school, and tetanus, diphtheria and acellular pertussis vaccine, which is applied when the child is 11 years old, and also to health staff who assist children under 1 year old and to the people who live with premature infants weighing less than 1.5 Kg. Children under 6 months are protected if the pregnant mother is vaccinated as from week 20 of gestation.
Source: CONICET press