African Institute for Mathematical Sciences Senegal
Recent publications
Management of the COVID-19 pandemic relies on molecular diagnostic methods supported by serological tools. Herein, we developed S-RBD- and N- based ELISA assays useful for infection rate surveillance as well as the follow-up of acquired protective immunity against SARS-CoV-2. ELISA assays were optimized using COVID-19 Tunisian patients’ sera and prepandemic controls. Assays were further validated in 3 African countries with variable endemic settings. The receiver operating curve was used to evaluate the assay performances. The N- and S-RBD-based ELISA assays performances, in Tunisia, were very high (AUC: 0.966 and 0.98, respectively, p < 0.0001). Cross-validation analysis showed similar performances in different settings. Cross-reactivity, with malaria infection, against viral antigens, was noticed. In head-to-head comparisons with different commercial assays, the developed assays showed high agreement. This study demonstrates, the added value of the developed serological assays in low-income countries, particularly in ethnically diverse populations with variable exposure to local endemic infectious diseases.
Background: Metabolic syndrome is known as a predictor of cardiovascular disease (CVD), a leading cause of death globally. The factors that comprise metabolic syndrome are on the rise in Sub-Saharan Africa, and data regarding the prevalence of metabolic syndrome in communities of aged less than 40 years old remain scarce. Methods: Data were collected between March and April 2013 from 3 regions of the Northern Senegal (i.e., Saint-Louis, Matam et and Louga) using a cluster sampling method and the survey base of the national statistical and demographical agency. Subjects aged between 18 and 80 years were recruited, however, the present study focused on adult populations below 40 years of age. Participants underwent a face-to-face questionnaire to collect demographics and data on cardiovascular history/risk factors. Blood pressure (BP) and anthropometric measurements were performed in addition to a blood test measuring fasting triglycerides, high density lipoprotein (HDL) and low-density lipoprotein (LDL) cholesterol, and plasma glucose. Metabolic syndrome was defined as fasting plasma glucose ≥110 mg/dl, serum triglycerides ≥150 mg/dl, serum HDL cholesterol <40 mg/dl, BP ≥130/85 mmHg or on BP medication, or waist girth >102 cm in males or >89 cm in females. Comparisons used the χ2 test for categorical variables and Student’s t test for continuous variables. Multiple logistic regression was used to identify factors associated with CFI, after considering potential confounders. Covariates with significant association (P<0.05) in univariate analysis were included in the multivariate logistic model. Results: Of the 2,440 subjects recruited, 1080 participants were less than 40 years old and included in the current analysis. The mean age of these participants was 31 ± 7.53I. There were 296 (27%) male participants in our study. . Overall, there were 41 participants (3.8%) with metabolic. For individual components of metabolic syndrome, body mass index of 25 or higher was present in 32% of the population with a significant increase among women (38 vs 15% vs 3,7%, p<0,001). The prevalence of hypertension was28% and more than half of the population presented with dyslipidaemia (554 participants). Among those with dyslipidemia, 339 have a high total cholesterol index (61%, 95% CI: 57-65%). Conclusion: Our community-based cross-sectional study revealed a low prevalence of metabolic syndrome among younger participants in northern Senegal. However, the prevalence of dyslipidaemia was high.
Background: Patients with renal failure have a higher risk or cardiovascular events. However, the prevalence of renal failure in Sub Saharan Africa communities remain poorly documented. Methods: Data were collected between March and April 2013 from 3 regions of the Northern Senegal (i.e., Saint-Louis, Matam et and Louga) using a cluster sampling method and the survey base of the national statistical and demographical agency subjects aged between 18 and 80 years. However, the present study focused on adult populations below 40 years of age. Participants underwent a face-to-face questionnaire to collect demographics and data on cardiovascular history/risk factors. Blood pressure and anthropometric measurements were performed in addition to blood tests including plasma creatinine. Renal failure was defined as a GFR < 60 ml/min/1.73 m ² using the MDRD method adapted to the African population. Continuous data were reported as mean ± standard deviation (SD). Comparisons used the χ2 test for categorical variables and Student’s t test for continuous variables. Multiple logistic regression was used to identify factors associated with CFI, after considering potential confounders. Covariates with significant association (P<0.05) in univariate analysis were included in the multivariate logistic model. Results: Among the 2440 subjects in this study the mean age was 44 ± 15.99, 692 (28%) were male. Among the 1080 participants who were aged less than 40 years old (mean: 31 ± 7.54), 296 (27.4%) were male. Body mass index higher than 25 was present in 32% of the studied population with a significant increase in women (38% vs 15%, p<0,001). The prevalence of hypertension was 28%. The prevalence of renal failure was 3.1% (95%CI: 2.1-4.3%) with a mean glomerular filtration rate of 55 ± 23.58. None of the participants with renal failure had diabetes. Conclusion: This community-based cross-sectional study showed a low prevalence of renal failure in younger participants in Northern Senegal. Further investigations are needed to assess chronic kidney failure and its determinants.
Vaccines against different SARS-CoV-2 variants have been approved, but continued surveillance is needed to determine when the antigen composition of vaccines should be updated, together with clinical studies to assess vaccine efficacy.
Covid-19 pandemic has negatively impacted many areas, including the economy and health care facilities, and has left more than 5 million deaths worldwide. In this paper, we use functional data analysis methods to describe evolution of the number of cases and the number of deaths of Covid-19 in Africa. We perform functional principal component analysis, Multivariate functional component analysis and spatial component analysis to characterize better the phenomena and spatial data to determine the impact of a region's neighborhood on number of cases. The obtained results allow us to have a better knowledge of the evolution of the pandemic in African continent.
On 10th September 2018, the Syndromic Sentinel Surveillance network that monitors febrile illnesses in all 14 regions of Senegal detected a peak of fever in the Fatick region. On 13 September 2018, 10 samples were sent to the WHO Collaborating Centre for Arboviruses and Viral Haemorrhagic Fevers at the Institut Pasteur de Dakar (IPD). Laboratory investigations revealed an epidemic of dengue 1 genotype V and dengue 3 genotype III. Fatick neighbors the Holy City of Touba where 3.5 million people from all over the word gather every year for the Grand Magal pilgrimage. This article discusses the impact of mass gatherings and their role in the recent introduction of dengue serotypes in Senegal. Dengue is now endemic in Senegal and across many countries in Africa, highlighting the need for early detection, control measures and prevention of severe dengue cases in highly connected urban settings.
The mosquito-borne disease caused by the Rift Valley Fever Virus (RVFV) is a viral hem-orrhagic fever that affects humans and animals. In 1987, RVFV emerged in Mauritania, which caused the first RVFV outbreak in West Africa. This outbreak was shortly followed by reported cases in humans and livestock in Senegal. Animal trade practices with neighboring Mauritania suggest northern regions of Senegal are at high risk for RVF. In this study, we aim to conduct a molecular and serological survey of RVFV in humans and livestock in Agnam (northeastern Senegal) by RT-PCR (reverse transcription real-time polymerase chain reaction) and ELISA (Enzyme-Linked Immunosorbent Assay), respectively. Of the two hundred fifty-five human sera, one (0.39%) tested RVFV IgM positive, while fifty-three (20.78%) tested positive for RVFV IgG. For animal monitoring, out of 30 sheep recorded and sampled over the study period, 20 (66.67%) showed seroconversion to RVFV IgG antibodies, notably during the rainy season. The presence of antibodies increased significantly with age in both groups (p < 0.05), as the force of RVF infection (FOI), increased by 16.05% per year for humans and by 80.4% per month for livestock sheep. This study supports the usefulness of setting up a One Health survey for RVF management. Citation: Mhamadi, M.; Badji, A.; Barry, M.A.; Ndiaye, E.H.; Gaye, A.; Ndiaye, M.; Mhamadi, M.; Touré, C.T.; Ndiaye, O.; Faye, B.; et al. Human and Livestock Surveillance Revealed the Circulation of Rift Valley Fever
Profiling of the antibody responses to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) proteins in African populations is scarce. Here, we performed a detailed IgM and IgG epitope mapping study against 487 peptides covering SARS-CoV-2 wild-type structural proteins. A panel of 41 pre-pandemic and 82 COVID-19 RT-PCR confirmed sera from Madagascar and Senegal were used. We found that the main 36 immunodominant linear epitopes identified were (i) similar in both countries, (ii) distributed mainly in the Spike and the Nucleocapsid proteins, (iii) located outside the RBD and NTD regions where most of the reported SARS-CoV-2 variant mutations occur, and (iv) identical to those reported in European, North American, and Asian studies. Within the severe group, antibody levels were inversely correlated with the viral load. This first antibody epitope mapping study performed in patients from two African countries may be helpful to guide rational peptide-based diagnostic assays or vaccine development.
Antimicrobial resistance (AMR) is a major threat to global health. Understanding the emergence, evolution, and transmission of individual antibiotic resistance genes (ARGs) is essential to develop sustainable strategies combatting this threat. Here, we use metagenomic sequencing to analyse ARGs in 757 sewage samples from 243 cities in 101 countries, collected from 2016 to 2019.We find regional patterns in resistomes, and these differ between subsets corresponding to drug classes and are partly driven by taxonomic variation. The genetic environments of 49 common ARGs are highly diverse, with most common ARGs carried by multiple distinct genomic contexts globally and sometimes on plasmids. Analysis of flanking sequence revealed ARG-specific patterns of dispersal limitation and global transmission. Our data furthermore suggest certain geographies are more prone to transmission events and should receive additional attention.
The African manatee (Trichechus senegalensis) is an elusive, data-deficient, and endangered species which inhabits marine and freshwater systems throughout Western and Central Africa. A major challenge in understanding the species ecology and distribution is the difficulty in detecting it using traditional visual surveys. The recent invasion of Giant Salvinia (Salvinia molesta) at the most important site for the species in Cameroon further limits their detectability and may restrict their movements and habitat use. To investigate methods’ effectiveness in detecting African manatees, we conducted monthly vessel surveys from which visual point scans, 360° sonar scans, and passive acoustic monitoring were conducted simultaneously at ten locations and over 12 months in Lake Ossa, Cameroon. Manatee detection frequency was calculated for each method and the influence of some environmental conditions on the methods’ effectiveness and manatee detection likelihood was assessed by fitting a binary logistic regression to our data. Detection frequencies were significantly different between methods (p < 0.01) with passive acoustics being the most successful (24.17%; n = 120), followed by the 360° sonar scan (11.67%; n = 120), and the visual point scan (3.33%; n = 120). The likelihood of detecting manatees in Lake Ossa was significantly influenced by water depth (p = 0.02) and transparency (p < 0.01). It was more likely to detect manatees in shallower water depths and higher water transparency. Passive acoustic detections were more effective in uninvaded areas of the Lake. We recommend using passive acoustics to enhance African manatee detections in future surveys.
The aim of the present paper is to study existence results of minimizers of the critical fractional Sobolev constant on bounded domains. Under some values of the fractional parameter we show that the best constant is achieved. If moreover the underlying domain is a ball, we obtain positive radial minimizers for all possible values of the fractional parameter in higher dimension, while we impose a positive mass condition in low dimension.
Malaria is a vector-borne disease that poses major health challenges globally, with the highest burden in children less than 5 years old. Prevention and treatment have been the main interventions measures until the recent groundbreaking highly recommended malaria vaccine by WHO for children below five. A two-group malaria model structured by age with vaccination of individuals aged below 5 years old is formulated and theoretically analyzed. The disease-free equilibrium is globally asymptotically stable when the disease-induced death rate in both human groups is zero. Descarte’s rule of signs is used to discuss the possible existence of multiple endemic equilibria. By construction, mathematical models inherit the loss of information that could make prediction of model outcomes imprecise. Thus, a global sensitivity analysis of the basic reproduction number and the vaccination class as response functions using Latin-Hypercube Sampling in combination with partial rank correlation coefficient are graphically depicted. As expected, the most sensitive parameters are related to children under 5 years old. Through the application of optimal control theory, the best combination of interventions measures to mitigate the spread of malaria is investigated. Simulations results show that concurrently applying the three intervention measures, namely: personal protection, treatment, and vaccination of childreen under-five is the best strategy for fighting against malaria epidemic in a community, relative to using either single or any dual combination of intervention(s) at a time.
Sero-surveillance can monitor and project disease burden and risk. However, SARS-CoV-2 antibody test results can produce false positive results, limiting their efficacy as a sero-surveillance tool. False positive SARS-CoV-2 antibody results are associated with malaria exposure, and understanding this association is essential to interpret sero-surveillance results from malaria-endemic countries. Here, pre-pandemic samples from eight malaria endemic and non-endemic countries and four continents were tested by ELISA to measure SARS-CoV-2 Spike S1 subunit reactivity. Individuals with acute malaria infection generated substantial SARS-CoV-2 reactivity. Cross-reactivity was not associated with reactivity to other human coronaviruses or other SARS-CoV-2 proteins, as measured by peptide and protein arrays. ELISAs with deglycosylated and desialated Spike S1 subunits revealed that cross-reactive antibodies target sialic acid on N-linked glycans of the Spike protein. The functional activity of cross-reactive antibodies measured by neutralization assays showed that cross-reactive antibodies did not neutralize SARS-CoV-2 in vitro. Since routine use of glycosylated or sialated assays could result in false positive SARS-CoV-2 antibody results in malaria endemic regions, which could overestimate exposure and population-level immunity, we explored methods to increase specificity by reducing cross-reactivity. Overestimating population-level exposure to SARS-CoV-2 could lead to underestimates of risk of continued COVID-19 transmission in sub-Saharan Africa.
In addition to emerging coronaviruses (SARS-CoV, MERS, SARS-CoV-2), there are seasonal human coronaviruses (HCoVs): HCoV-OC43, HCoV-229E, HCoV-NL63 and HCoV-HKU1. With a wide distribution around the world, HCoVs are usually associated with mild respiratory disease. In the elderly, young children and immunocompromised patients, more severe or even fatal respiratory infections may be observed. In Africa, data on seasonal HCoV are scarce. This retrospective study investigated the epidemiology and genetic diversity of seasonal HCoVs during nine consecutive years of influenza-like illness surveillance in Senegal. Nasopharyngeal swabs were collected from ILI outpatients or from SARI hospitalized patients. HCoVs were diagnosed by qRT-PCR and the positive samples were selected for molecular characterization. Among 9337 samples tested for HCoV, 406 (4.3%) were positive: 235 (57.9%) OC43, 102 (25.1%) NL63, 58 (14.3%) 229E and 17 (4.2%) HKU1. The four types circulated during the study period and a peak was noted between November and January. Children under five were the most affected. Co-infections were observed between HCoV types (1.2%) or with other viruses (76.1%). Genetically, HCoVs types showed diversity. The results highlighted that the impact of HCoVs must be taken into account in public health; monitoring them is therefore particularly necessary both in the most sensitive populations and in animals.
Dengue virus (DENV) was detected in Senegal in 1979 for the first time. Since 2017, unprecedented frequent outbreaks of DENV were noticed yearly. In this context, epidemiological and molecular evolution data are paramount to decipher the virus diffusion route. In the current study, we focused on a dengue outbreak which occurred in Senegal in 2018 in the context of a large religious gathering with 263 confirmed DENV cases out of 832 collected samples, including 25 life-threatening cases and 2 deaths. It was characterized by a co-circulation of dengue serotypes 1 and 3. Phylogenetic analysis based on the E gene revealed that the main detected serotype in Touba was DENV-3 and belonged to Genotype III. Bayesian phylogeographic analysis was performed and suggested one viral introduction around 2017.07 (95% HPD = 2016.61–2017.57) followed by cryptic circulation before the identification of the first case on 1 October 2018. DENV-3 strains are phylogenetically related, with strong phylogenetic links between strains retrieved from Burkina Faso and other West African countries. These phylogenetic data substantiate epidemiological data of the origin of DENV-3 and its spread between African countries and subsequent diffusion after religious mass events. The study also highlighted the usefulness of a mobile laboratory during the outbreak response, allowing rapid diagnosis and resulting in improved patient management.
In this work we study nonlocal operators and corresponding spaces with a focus on operators of order near zero. We investigate the interior regularity of eigenfunctions and of weak solutions to the associated Poisson problem depending on the regularity of the right-hand side. Our method exploits the variational structure of the problem and we prove that eigenfunctions are of class $$C^{\infty }$$ C ∞ if the kernel satisfies this property away from its singularity. Similarly in this case, if in the Poisson problem the right-hand is of class $$C^{\infty }$$ C ∞ , then also any weak solution is of class $$C^{\infty }$$ C ∞ .
Background The Omicron variant B.1.1.529 has led to a new dynamic in the COVID-19 pandemic, with an increase in cases worldwide. Its rapid propagation favors the emergence of novel sub-lineages, including BA.4 and BA.5. The latter has shown increased transmissibility compared to other Omicron sub-lineages. In Senegal, the emergence of the Omicron variant in December 2021 characterized the triggering of a short and dense epidemiological wave that peaked at the end of February. This wave was followed by a period with a significant drop in the number of COVID-19 cases, but an upsurge in SARS-CoV-2 infection has been noted since mid-June. Objective The purpose of this brief report is to give an update regarding the genomic situation of SARS-CoV-2 in Dakar during this phase of recrudescence of cases. Methods We performed amplicon-based SARS-CoV-2 sequencing on nasopharyngeal swab samples from declared COVID-19 patients and outbound travelers that tested positive. Results Ongoing genomic surveillance activities showed that more than half of recent COVID-19 cases were due to the BA.4 and BA.5 sub-lineages that share two critical mutations associated with increased transmissibility and immune response escape. The circulation of recombinants between Omicron sub-lineages was also noted. Conclusion Despite the lack of proven severity of BA.4 and BA.5 sub-lineages, their increased transmissibility causes a rapid spread of the virus, hence a surge in the number of cases. This rapid spread constitutes a greater risk of exposure for vulnerable patients. To tackle this issue, any increase in the number of cases must be monitored to support public health stakeholders. Therefore, genomic surveillance is an ever-essential element in managing this pandemic.
Senegal is hyperendemic for dengue. Since 2017, outbreaks have been noticed annually in many regions around the country, marked by the co-circulation of DENV1-3. On 8 October 2021, a Dengue virus outbreak in the Rosso health post (sentinel site of the syndromic surveillance network) located in the north of the country was notified to the WHO Collaborating Center for arboviruses and hemorrhagic fever viruses at Institut Pasteur de Dakar. A multidisciplinary team was then sent for epidemiological and virologic investigations. This study describes the results from investigations during an outbreak in Senegal using a rapid diagnostic test (RDT) for the combined detection of dengue virus non-structural protein 1 (NS1) and IgM/IgG. For confirmation, samples were also tested by real-time RT-PCR and IgM ELISA at the reference lab in Dakar. qRT-PCR positive samples were subjected to whole genome sequencing using nanopore technology. Virologic analysis scored 102 positives cases (RT-PCR, NS1 antigen detection and/or IgM) out of 173 enrolled patients; interestingly, virus serotyping showed that the outbreak was caused by the DENV-1, a serotype different from DENV-2 involved during the outbreak in Rosso three years earlier, indicating a serotype replacement. Nearly all field-tested NS1 positives samples were confirmed by qRT-PCR with a concordance of 92.3%. Whole genome sequencing and phylogenetic analysis of strains suggested a re-introduction in Rosso of a DENV-1 strain different to the one responsible for the outbreak in the Louga area five years before. Findings call for improved dengue virus surveillance in Senegal, with a wide deployment of DENV antigenic tests, which allow easy on-site diagnosis of suspected cases and early detection of outbreaks. This work highlights the need for continuous monitoring of circulating serotypes which is crucial for a better understanding of viral epidemiology around the country.
West Nile virus (WNV) is a virus of the Japanese encephalitis antigenic complex and belongs to the family Flaviviridae of the genus flavivirus. The virus can cause infection in humans which in most cases is asymptomatic, however symptomatic cases exist and the disease can be severe causing encephalitis and meningoencephalitis. The virus is maintained in an enzootic cycle involving mosquitoes and birds, humans and other mammals such as horses can be accidental hosts. A mosquito-based arbovirus surveillance system and the sentinel syndromic surveillance network (4S) have been in place since 1988 and 2015 respectively, to better understand the transmission dynamics of arboviruses including WNV in Senegal. Arthropod and human samples have been collected from the field and analysed at Institut Pasteur de Dakar using different methods including RT-PCR, ELISA, plaque reduction neutralization test and viral isolation. RT-PCR positive samples have been analysed by Next Generation Sequencing. From 2012 to 2021, 7912 samples have been analysed and WNV positive cases have been detected, 20 human cases (19 IgM and 1 RT-PCR positive cases) and 41 mosquito pools. Phylogenetic analyzes of the sequences of complete genomes obtained showed the circulation of lineage 1a, with all these recent strains from Senegal identical to each other and very close to strains isolated from horse in France in 2015, Italy and Spain. Our data showed lineage 1a endemicity in Senegal as previously described, with circulation of WNV in humans and mosquitoes. Phylogenetic analyzes carried out with the genome sequences obtained also revealed exchanges of WNV strains between Europe and Senegal which could be possible via migratory birds. The surveillance systems that have enabled the detection of WNV in humans and arthropods should be extended to animals in a one-health approach to better prepare for global health threats.
Institution pages aggregate content on ResearchGate related to an institution. The members listed on this page have self-identified as being affiliated with this institution. Publications listed on this page were identified by our algorithms as relating to this institution. This page was not created or approved by the institution. If you represent an institution and have questions about these pages or wish to report inaccurate content, you can contact us here.
157 members
Mouhamed Moustapha Fall
  • Mathematics and its Applications
Lionel Tondji
  • Program in Mathematics and its Applications
Isaac Felix
  • Mathematical Science
Samuel Oladimeji Sowole
  • Program in Mathematics and its Applications
Road to Joal (IRD center), Dakar, Mbour, Senegal