Seroprevalence of pertussis in Senegal: a prospective study
Gaayeb L, Sarr JB, Ndiath MO, Hanon JB, Debrie AS, Seck M, Schacht AM, Remoué F, Hermann E, Riveau G.
PLoS One, 2012, 7(10):e48684 (PMID : 23119090)
The purpose of this longitudinal study was to investigate seroprevalence of Pertussis (also known as whooping cough) in children from Northern Senegal, and to gain some insight on the evolution of these children’s humoral response towards pertussis antigens over 18 months. This work has confirmed the age-dependent response profile to whooping cough previously observed in industrialized countries. Moreover, our study has shed a light over the circulation of Bordetella pertussis in this sub-Saharan location. Finally, we have demonstrated that while some of the studied villages were endemic for B. pertussis, an outbreak has occurred in another village during the course of our study. We are convinced that assessing the seroprevalence of Pertussis in Northern Senegal is essential in the frame of monitoring the impact of the Expanded Program for Immunization from the World Health Organization on immunity to this vaccine-preventable respiratory disease in this particular setting.
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BACKGROUND:
Pertussis, also known as whooping cough, is a vaccine-preventable respiratory disease caused by Bordetella pertussis infection, against which Senegalese children are immunized with the diphtheria-tetanus-whole cell pertussis vaccine (DTwP). Seroepidemiology of pertussis has been widely described in industrialized countries, but rare are the studies referring to it in developing countries.
METHODS:
We conducted a longitudinal survey in Northern Senegal to investigate the epidemiology of B. pertussis by evaluating the IgG antibody (Ab) response against pertussis toxin (PT). A cohort of 410 children aged 1 to 9 from five villages in the Middle Senegal River Valley were followed-up for 18 months. During that period, five visits were made to assess the immunological status of the children.
PRINCIPAL FINDINGS:
PT-specific IgG responses were significantly different according to age. Until the age of 3, there was a decrease in the Ab response, which then increased in the older groups. Assessment of IgG antibodies to PT (IgG-PT) suggested evidence of recent exposures to the pathogen. Surprisingly, in one of the five villages the average Ab response to PT was very low at all ages during the first 6 months of the study. At the third visit, IgG-PT concentrations peaked to very high levels, to slightly decline at the end of the survey. This indicates an outbreak of B. pertussis, whereas in the other villages a pertussis endemic profile could be observed.
CONCLUSIONS:
Pertussis is endemic in Northern Senegal despite the introduction of vaccination. The circulation of the bacteria seems to differ between geographic locations and over time. A more complete understanding of the epidemiology of pertussis and its environmental determinants could provide information to adapt vaccination programs.