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Introduction: Asymptomatic carriage of P. falciparum is frequent in areas endemic for malaria and individual diagnosis of clinical malaria attacks is still difficult. We investigated the impact of changes in malaria endemicity on the diagnostic criteria for malaria attacks in an area of seasonal malaria transmission. Methods: We analyzed the longitudinal data collected over 20 years from a daily survey of all inhabitants of Ndiop, a rural community in central Senegal, in a logistic regression model to investigate the relationship between the level of Plasmodium falciparum parasitemia and the risk of fever, with the aim of determining the best parasitemia thresholds for attributing to malaria a fever episode. Results: A total of 34,136 observations recorded from July 1993 to December 2013 from 850 individuals aged from 1 day to 87 years were included. P. falciparum asymptomatic carriage declined from 36% to 1% between 1993 and 2013. A total of 9,819 fever episodes were associated with a positive blood film for P. falciparum. Using age-dependent parasitemia thresholds for attributing to malaria a fever episode, we recorded 6,006 malaria attacks during the study period. Parasitemia thresholds seemed to be lower during the low-to-zero transmission season and tended to decrease with changes in control policies. The number of clinical malaria attacks was overestimated for all age groups throughout the study when all fever episodes associated with P. falciparum parasitemia were defined as malaria attacks. Conclusion: Pyrogenic thresholds are particularly sensitive to changes in malaria epidemiology and are therefore an interesting tool to accurately assess the burden of malaria in the context of declining transmission. [ABSTRACT FROM AUTHOR]

Background: In the progress towards malaria elimination, the accurate diagnosis of low-density asymptomatic infections is critical. Low-density asymptomatic submicroscopic malaria infections may act as silent reservoirs that maintain low-level residual malaria transmission in the community. Light microscopy, the gold standard in malaria diagnosis lacks the sensitivity to detect low-level parasitaemia. In this study, the presence and prevalence of submicroscopic Plasmodium carriage were investigated to estimate the parasites reservoir among asymptomatic individuals living in low transmission areas in Dielmo and Ndiop, Senegal during the dry season. Methods: A total of 2,037 blood samples were collected during cross-sectional surveys prior the malaria transmission season in July 2013 (N = 612), June 2014 (N = 723) and June 2015 (N = 702) from asymptomatic individuals living in Dielmo and Ndiop, Senegal. Samples were used to determine the prevalence of submicroscopic Plasmodium carriage by real time PCR (qPCR) in comparison to microscopy considered as gold standard. Results: The prevalence of submicroscopic Plasmodium carriage was 3.75% (23/612), 12.44% (90/723) and 6.41% (45/702) in 2013, 2014 and 2015, respectively. No Plasmodium carriage was detected by microscopy in 2013 while microscopy-based prevalence of Plasmodium carriage accounted for only 0.27% (2/723) and 0.14% (1/702) in 2014 and 2015, respectively. Plasmodium falciparum accounted for the majority of submicroscopic infections and represented 86.95% (20/23), 81.11% (73/90) and 95.55 (43/45) of infections in 2013, 2014 and 2015 respectively. Conclusion: Low-density submicroscopic asymptomatic Plasmodium carriage is common in the study areas during the dry season indicating that traditional measures are insufficient to assess the scale of parasite reservoir when transmission reaches very low level. Control and elimination strategies may wish to consider using molecular methods to identify parasites carriers to guide Mass screening and Treatment strategies. [ABSTRACT FROM AUTHOR]

Background: African populations are considered to be particularly vulnerable to fever illnesses, including malaria, and acute respiratory disease, owing to limited resources and overcrowding. However, the overall burden of influenza in this context is poorly defined and incidence data for African countries are scarce. We therefore studied the fever syndrome incidence and more specifically influenza incidence in a cohort of inhabitants of Dielmo and Ndiop in Sokone district, Senegal. Methods: Daily febrile-illness data were prospectively obtained from January 2012 to December 2013 from the cohort of the villages of Dielmo and Ndiop, initially dedicated to the study of malaria. Nasopharyngeal swabs were collected from, and malaria diagnosis tests (thick blood smears) carried out on, every febrile individual during clinical visits; reverse transcriptase-polymerase chain reaction was used to identify influenza viruses in the samples. Binomial negative regression analysis was used to study the relationship between the monthly incidence rate and various covariates. Results: In Dielmo and Ndiop, the incidence of malaria has decreased, but fever syndromes remain frequent. Among the 1036 inhabitants included in the cohort, a total of 1,129 episodes of fever were reported. Influenza was present all year round with peaks in October-December 2012 and August 2013. The fever, ILI and influenza incidence density rates differed significantly between age groups. At both sites, the adjusted incidence relative risks for fever syndromes and ILI were significantly higher in the [6–24 months) than other age groups: 7.3 (95%CI: [5.7–9.3]) and 16.1 (95%CI: [11.1–23.3]) respectively. The adjusted incidence relative risk for influenza was significantly higher for the [0–6 months) than other age groups: 9.9 (95%CI: [2.9–33.6]). At both sites, incidence density rates were lowest among adults > = 50 years. Conclusions: In this rural setting in Senegal, influenza was most frequent among the youngest children. Preventive strategies targeting this population should be implemented. [ABSTRACT FROM AUTHOR]

Introduction: Malaria is a leading cause of morbidity and mortality in sub-Saharan Africa. Detailed characterization of the risks for malaria, among populations living in areas where the disease is endemic, is an important priority, especially for planning and evaluating future malaria-control tools. A prospective cohort study was implemented in children under ten years living in rural areas with high Plasmodium falciparum transmission in Senegal. Methods: Malaria incidence was prospectively evaluated over three year follow-up among a cohort of children aged less than 10 years old living in eight villages of the Sokone health district. The parents of 1316 children comprising a passive case detection cohort were encouraged to seek care from the study health centers at any time their child felt sick. In the event of reported history of fever within 24 hours or measured axillary temperature ≥ 37.5°C, a Rapid Diagnostic Test (RDT) was performed. Results: From November 2010 to October 2013, among the 1468 reported febrile episodes, 264 were confirmed malaria episodes. Over the 3 years, 218 (16.9%) children experienced at least one clinical malaria episode. Cumulative malaria incidence was 7.3 episodes per 100 children-year at risk, with remarkably heterogeneous rates from 2.5 to 10.5 episodes per 100 children-year at risk. Clinical malaria prevalence ranged from 11.5 to 28.4% in the high transmission season versus from 9.6 to 21.2% in the low transmission season. Conclusion: This longitudinal community-based study shows that occurrence of clinical malaria was not evenly distributed among all the cohort children in the eight villages. It demonstrates the complexity of spatial distribution of malaria incidence at a local level, even in a region of vegetation and altitudinal homogeneity. [ABSTRACT FROM AUTHOR]

Influenza surveillance in African countries was initially restricted to the identification of circulating strains. In Senegal, the network has recently been enhanced (i) to include epidemiological data from Dakar and other regions and (ii) to extend virological surveillance to other respiratory viruses. Epidemiological data from the sentinel sites is transmitted daily by mobile phone. The data include those for other febrile syndromes similar to influenza-like illnesses (ILI), corresponding to integrated approach. Also, clinical samples are randomly selected and analyzed for influenza and other respiratory viruses. There were 101,640 declared visits to the 11 sentinel sites between week 11-2012 and week 35-2013; 22% of the visits were for fever syndromes and 23% of the cases of fever syndrome were ILI. Influenza viruses were the second most frequent cause of ILI (20%), after adenoviruses (21%) and before rhinoviruses (18%) and enteroviruses (15%). Co-circulation and co-infection were frequent and were responsible for ILI peaks. The first months of implementation of the enhanced surveillance system confirmed that viruses other the influenza make large contributions to influenza-like illnesses. It is therefore important to consider these etiologies in the development of strategies to reduce respiratory infections. More informative tools and research studies are required to assess the burden of respiratory infections in developing countries. [ABSTRACT FROM AUTHOR]

There exists great disparity in the number of clinical P. falciparum episodes among children of the same age and living in similar conditions. The epidemiological determinants of such disparity are unclear. We used a data-mining approach to explore a nineteen-year longitudinal malaria cohort study dataset from Senegal and identify variables associated with increased risk of malaria episodes. These were then verified using classical statistics and replicated in a second cohort. In addition to age, we identified a novel high-risk group of children in whom the history of P. falciparum clinical episodes greatly increased risk of further episodes. Age and a high number of previous falciparum clinical episodes not only play major roles in explaining the risk of P. falciparum episodes but also are risk factors for different groups of people. Combined, they explain the majority of falciparum clinical attacks. Contrary to what is widely believed, clinical immunity to P. falciparum does not de facto occur following many P. falciparum clinical episodes. There exist a sub-group of children who suffer repeated clinical episodes. In addition to posing an important challenge for population stratification during clinical trials, this sub-group disproportionally contributes to the disease burden and may necessitate specific prevention and control measures. [ABSTRACT FROM AUTHOR]