Abstract
In Madagascar, among the threats to public health, the population is faced with infectious diseases that can affect the entire population and constitute permanent health risks, such as Plasmodium falciparum (P. falciparum) infection and other endemic infectious diseases such as the plague, as well as emerging diseases such as COVID-19. The epidemiological surveillance system and national infectious disease control programmes have also been tested in the context of the COVID-19 pandemic. According to the World Health Organization (WHO), during the 2020-2021 pandemic period, approximately 82% of cases and 95% of deaths due to malaria worldwide occurred in the WHO African Region, representing an increase in cases, from 211 million to 234 million, and deaths, from 542,000 to 593,000, from 2015-2020. Furthermore, between 2020 and 2021, approximately 13.4 million additional malaria cases, and an increase in deaths from 386,400 to 597,400, would have been attributable to the mitigation of control efforts due to non-pharmaceutical interventions to address the COVID-19 pandemic. Our aim in this thesis is to gain a better understanding of the spatial and temporal dynamics of two infectious diseases, malaria and COVID-19, despite the porosity (set of shortcomings) of the passive surveillance system in Madagascar. To this end, biostatistical and biomathematical modelling approaches were adopted using data from indirect measures of transmission intensity: P. falciparum antibody measurements, and all-cause excess mortality during the COVID-19 pandemic. The first study in this thesis uses data from a randomized cross-sectional study involving 6,293 children to identify factors associated with residual malaria transmission in the highlands, an area of very low transmission. Factors related to the health care services (access to health facilities, community-based case management, vector control interventions) and to the environment and climate (vector ecology) were studied. The second study consists of assessing the impact of the COVID-19 pandemic in the capital, Antananarivo, by estimating the excess deaths during the 2020–2021 waves using the death registers referring to the Bureau Municipal d’Hygiène, representing 45,959 records of hospital and community deaths from 2016–2021. Our results from these two studies have highlighted the importance of fine-scale disaggregated spatial or temporal data (antibody responses, environmental and climatic factors) and optimal surveillance systems (death registers) for evaluating, improving and adapting national infectious disease control programmes in low- and middle-income countries such as Madagascar. Keywords: epidemiology, modelling, surveillance systems, spatial and temporal analyses, malaria, Plasmodium falciparum, COVID-19, SARS-CoV-2, excess mortality, Madagascar.