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Project : Long-term epidemiology of Meningococcal Meningitis in the African belt: dynamics and impact of vaccination. Spatio-temporal dynamics (spread, persistence, periodicity), Comparative approach, impact of vaccination. Hélène Broutin, PhD
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Project :Long-term epidemiology of Meningococcal Meningitis in the African belt: dynamics and impact of vaccination Spatio-temporal dynamics (spread, persistence, periodicity), Comparative approach, impact of vaccination Hélène Broutin, PhD Post-doctoral researcher (Supervisor: Dr Mark A. Miller) Division of International Epidemiology and Population Studies, Fogarty International Center, National Institutes of Health GEO Meningitis Environmental Risk Consultative Meeting, 26-27 sept 2007, WHO, Geneva
Questions and goals … Better mechanistic understanding of the epidemiology of MM during recent decades(emergence, diffusion, persistence) • Idea = studying the past (long time series) and comparing dynamics in order to: • - detect global patterns vs specialty • understand the impact of vaccination • be able to suggest adapted vaccination strategies • For which population size does the disease persist in time ? • Can we identify sources of infection (does a same locality or district constantly suffer first cases of an epidemic ?) • Do we observe similar routes of transmission of the disease in all countries ? • Do we observe synchrony of epidemics between countries ? Do we observe regular waves of cases ? GEO Meningitis Environmental Risk Consultative Meeting, 26-27 sept 2007, WHO, Geneva
Concepts when Ecology meets Epidemiology… = POPULATION of POPULATIONS CONNECTED BY MIGRATIONS Epidemiology Metapopulation => POPULATION SIZE Critical Community Size(CCS) Ecology PERSISTENCE IMPACT of VACCINATION ? => POPULATION FLUX concept cities /villages SPREAD
Concepts when Ecology meets Epidemiology… • PERSISTANCE : Critical Community Size (CCS) = • the minimal population size below which a disease cannot persist in a susceptible population without external input(s) • [Bartlett M.S., 1957; Black F.L., 1966; Anderson R.M. & May R.M., 1991; Grenfell B.T. & Harwood J., 1997] analyses of time-period of disease extinction (period with no new cases in a locality) in relation with the population size • DIFFUSION : concept cities / villages= diseases spread from big cities to villages • [Anderson R.M. & May R.M, 1991; Grenfell B.T. & Bolker B.M., 1998] Cases time series analyses between localities
Concepts when Ecology meets Epidemiology… Species maintain Population dynamics(Extinction-recolonization concept) extinction risk for the species
Concepts when Ecology meets Epidemiology… Population dynamicsand Epidemiology(Periodicities - synchronism) Best control Disease persistence These questions are also highly relevant in a global control perspective
Spatio-temporal dynamics of MM in Africa • Periodicity / synchrony GLOBAL –SCALE NATIONAL SCALE(inter-district) Mali LOCAL–SCALE (intra – district) Sikasso District Not only considered epidemics periods (e.g.1994 and 1996) but also inter-epidemics (i.e. 1993 to 1996) to make the link between epidemics) Persistence / Diffusion in relation with population size : can we detect sources of infection ? GEO Meningitis Environmental Risk Consultative Meeting, 26-27 sept 2007, WHO, Geneva
Illustrations … A) B) Figure extracted from Broutin H, Mantilla-Breniers N. and P. Rohani , Ecology of infectious disease:an example with two vaccine-preventable infectious diseases. Chapt 12 In ‘Encyclopediae of infectious diseases”, in press GEO Meningitis Environmental Risk Consultative Meeting, 26-27 sept 2007, WHO, Geneva
Different steps … Data Data analyses • - local persistence of the disease in a long-term • local to global diffusion patterns of MM • comparison between countries Detailed and long epidemiological time series : Weekly, by district • - spatial and temporal persistence of serotype in population • periodicity and route of transmission of different serotypes? • quantifying lags between serotypes dynamics Genetics data (serotype) Vaccination data - impact of vaccination on these dynamics ALL THESE analyses will allow a BETTER comprehension in order to be able to Model dynamics of the disease GEO Meningitis Environmental Risk Consultative Meeting, 26-27 sept 2007, WHO, Geneva
Integration of all components … Population size Genotype Vaccine status Climate Limits / questions Last of immunity ? Proportion of asymptomatic carrier? GEO Meningitis Environmental Risk Consultative Meeting, 26-27 sept 2007, WHO, Geneva
Collaboration with Dr MP. Préziosi from the WHO (Vaccine Program Initiative) • Dr Pejman Rohani, University of Georgia, Athens, GA, USA. • Availability of detailed data: on MM cases, vaccination and serotype, weekly data, for different countries…. Thank you for your attention GEO Meningitis Environmental Risk Consultative Meeting, 26-27 sept 2007, WHO, Geneva