La santé des pasteurs mobiles au Sahel – Bilan de 15 années de recherches et développement

Dans le Sahel, entre la Mauritanie et la Somalie incluant le Nord Kenya, environ 20 à 30 millions de personnes vivent en transhumance. Le rythme de leur migration suit l’évolution saisonnière du climat et la disponibilité des ressources, telle que l'eau, le pâturage et le sel. Malgré une exposition élevée à certaines maladies comme les zoonoses et les problèmes conditionnés liés au climat, les pasteurs mobiles sont parmi les populations quasiment exclues du système de santé, car la mise à disposition des services sociaux adaptés à un mode de vie mobile est difficile. Suivant l'objectif de recherche d'un meilleur accès aux soins des pasteurs mobiles, l'Institut Tropical et de Santé Publique Suisse, en partenariat avec plusieurs institutions dans la région, est actif au Sahel depuis 15 ans, aussi bien dans le domaine de la recherche, que celui des actions de développement. Basées sur une approche orientée vers les besoins des pasteurs mobiles pour leur développement, des recherches interdisciplinaires ont contribué à mieux comprendre la situation et les problèmes des éleveurs. En relation de la proximité entre l'homme et son bétail, une approche unissant la santé humaine et animale s'est avérée bonne et la valeur ajoutée d'une meilleure collaboration entre médecine humaine, animale et l'environnement a été démontrée. Ces approches utiles devraient être poursuivies et consolidées dans les recherches et le développement des actions futurs.     

COVID-19: A pluralistic and integrated approach for efficient management of the pandemic

The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which triggered the ongoing pandemic, was first discovered in China in late 2019. SARS-CoV-2 is a respiratory virus responsible for coronavirus disease 2019 (COVID-19) that often manifests as a pneumonic syndrome. In the context of the pandemic, there are mixed views on the data provided by epidemiologists and the information collected by hospital clinicians about their patients. In addition, the literature reports a large proportion of patients free of pneumonia vs a small percentage of patients with severe pneumonia among confirmed COVID-19 cases. This raises the issue of the complexity of the work required to control or contain the pandemic. We believe that an integrative and pluralistic approach will help to put the analyses into perspective and reinforce collaboration and creativity in the fight against this major scourge. This paper proposes a comprehensive and integrative approach to COVID-19 research, prevention, control, and treatment to better address the pandemic. Thus, this literature review applies a pluralistic approach to fight the pandemic.     

Urinary biomarkers of aflatoxin exposure in young children from Egypt and Guinea.

Aflatoxins are a major risk factor for hepatocellular carcinoma (HCC), and thus understanding the pattern of aflatoxin exposure in different regions is important in order to develop targeted intervention strategies. Given the early onset of HCC in many countries early life exposures may be important. This study investigated aflatoxin exposure in Egyptian children (n=50, aged 1-2.5 years) by assessing urinary aflatoxin metabolite (AFM(1), AFB(1), AFB(2), AFG(1), AFG(2)) levels. Samples from Guinean children (n=50, aged 2-4 years) were analyzed in parallel providing a comparison to a region of established frequent aflatoxin exposure. Aflatoxins were isolated from urine using C18-cartridges followed by immunoaffinity clean-up, and quantified by HPLC with fluorescence detection. Overall aflatoxins were less frequently present in Egyptian (38%) than Guinean urine samples (86%) (p<0.001), which was particularly related to differences in detection rates of AFM(1) (8% compared to 64%, respectively, (p<0.001)). For AFM(1) the geometric mean level in Guinea (16.3 pg/ml; 95% CI: 10.1, 26.6 pg/ml) was 6-fold higher (p<0.001) than in Egypt (2.7 pg/ml; 95% CI: 2.5, 2.8 pg/ml). Urinary aflatoxins from healthy children in these two regions have not previously been reported, and exposure appears modest in Egypt compared to Guinea. These data suggest that measures to reduce aflatoxin exposure in both regions are important, though particularly in Guinea.     

Epidemiology of pertussis in a West African community before and after introduction of a widespread vaccination program

The control of pertussis remains a worldwide concern. Little has been documented about its epidemiology in Africa. The authors have studied pertussis in a prospective cohort of children in a rural West African community over a 13-year period comprising time before and after introduction of a vaccination program. Children under age 15 years who were residents of the Niakhar study area in Senegal were followed prospectively between January 1984 and December 1996 for the occurrence of pertussis. Morbidity and mortality rates were extremely high before the launch of immunization. Crude incidence was 183 per 1,000 child-years at risk under age 5 years, with a 2.8% case-fatality rate. After the introduction of the vaccination program, overall incidence dropped rapidly and dramatically-by 27% after 3 years and 46% after 6 years. The decline in incidence involved all age groups but was most substantial in the group under age 5 years and was particularly pronounced in unvaccinated infants. The median age of acquisition of the disease rose steadily with population vaccine coverage. This study shows the tremendous magnitude of the disease burden in children and the rapid decline after vaccination, and it suggests a strong herd-immunity effect.     

Quantitative comparison of aflatoxin B1 serum albumin adducts in humans by isotope dilution mass spectrometry and ELISA.

Metabolic activation of the hepatocarcinogenic mycotoxin aflatoxin B(1) (AFB(1)) results in the covalent attachment of AFB(1) to serum albumin. Digestion of adducted albumin releases AFB(1)-lysine, a biomarker of exposure status. AF-albumin adducts have been most frequently measured in precipitated serum albumin using an immunoassay (ELISA); however, a sensitive and specific isotope dilution mass spectrometric (IDMS) assay for measurement of AFB(1)-lysine in serum has recently been developed. The ELISA and IDMS methods were compared using 20 human sera collected in Guinea, West Africa, where AF exposure is endemic. Measurement of AFB(1)-lysine adduct concentrations by IDMS in serum and albumin precipitated from the same sample revealed that precipitation has no effect on the measured adduct levels. The concentration of AF-albumin adducts measured by ELISA and AFB(1)-lysine measured by IDMS in 2 mg of albumin were well correlated (R = 0.88, P < 0.0001); however, AF-albumin adduct concentrations measured by ELISA were on average 2.6-fold greater than those of the AFB(1)-lysine adduct. Although these data suggest that the ELISA is measuring other AF adducts in addition to AFB(1)-lysine, these biomarkers are comparable in their ability to assess AF exposure at AF-albumin concentrations > or =3 pg AFB(1)-lysine equivalents/mg albumin. Identification of other adducts may clarify the mechanistic basis for using AF-protein biomarkers to assess exposure status in future epidemiologic studies of liver cancer.     

Septo-hippocampal and nBM-cortical cholinergic neurones exhibit differential time-courses of activation as a function of both type and duration of spatial memory testing in mice

We previously showed that the initial acquisition session of a spatial discrimination (mixed reference/working memory) test in an 8-arm radial maze induced differential activations in the ascending cholinergic septo-hippocampal and nBM-cortical pathways in mice. This data showed that the duration of post-test cholinergic activation was longer in the nBM-cortical pathway than in the septo-hippocampal projection. Moreover, the post-test durations but not the immediate post-test amplitudes of activation in each pathway decreased progressively as a function of repeated daily acquisition sessions. In the present study we have thus tested the hypotheses that the time-courses of post-test cholinergic activation in the septo-hippocampal and nBM-cortical pathways may vary both as a function of the type of memory used (working vs. reference) and according to the duration of repeated daily testing. Cholinergic activity in vivo in the hippocampus or frontal cortex of mice was quantified using measures of sodium-dependent high-affinity choline uptake at two different times (30 s and 15 min) following specific spatial working or reference memory testing in an 8-arm radial maze. The memory tests were administered daily over a 13-day period to attain high levels of performance in each type of task. In comparison to control groups both types of memory testing induced significant post-test cholinergic activations in each brain region on Day 15. However, cholinergic activity remained elevated in frontal cortex at 15 min post-test following reference memory testing, whereas significantly shorter durations of cortical and hippocampal cholinergic activation were observed following working memory testing using short (1 min) retention intervals. The possible significance of these differential modifications to the time-course of the post-test activations in these cholinergic pathways in working and reference memory processes and the putative transsynaptic mechanisms involved are discussed.     

Plasmodium falciparum transmission blocking immunity in three areas with perennial or seasonal endemicity and different levels of transmission

Plasmodium falciparum transmission blocking immunity (TBI) was investigated in 3 different endemic areas. Reared Anopheles gambiae s.s. were experimentally infected with the blood of gametocyte carriers, either in the presence of autologous plasma (OWN) or after replacement of the OWN plasma with a nonimmune serum of AB blood group (control). Transmission reduction was defined by a lower level of mosquito infection in the OWN batch compared with the control. After controlling for the effect of gametocytemia, the proportion of "transmission reducers" was lower in the town of Yaounde in Cameroon (UC), (14%, N = 75) than in the two rural areas of South Cameroon (RC) (29%, N = 31) and Sénégal (RS) (44%, N = 32). The contribution of TBI relative to the total inhibition of the parasite development (including human, parasite, and mosquito factors) was higher in RS (49.6%) than in RC (12.6%) and UC (9.5%).     

Unaffordable or cost-effective?: introducing an emergency referral system in rural Niger

OBJECTIVES: An important investment was made in two health districts in Niger to organize an emergency referral system. This study estimates its impact and cost-effectiveness in relation with external determinants. METHODS: After installing a solar radio network in the health centres, emergency calls and related data were monitored over 7 years and investment and recurrent costs for the system were estimated. RESULTS: The number of emergency calls increased significantly in both districts. In 2003, the total yearly cost for the district amounted to US dollars 14,147, the cost per useful and successful call was US dollars 49 and the cost per inhabitant and per year was about US dollars 0.06. CONCLUSION: The impressive and immediate impact on the health system, the relatively low recurrent cost and the minimal management requirements for the health service make the investment very worthwhile. Organizing emergency evacuation systems should be a priority for any health district in the world.     

Risk factors for acellular and whole-cell pertussis vaccine failure in Senegalese children

Although use of acellular pertussis vaccine was associated with a higher rate of vaccine failure than that of whole-cell vaccine in the Senegal Pertussis Trial conducted in 1990-1994 on 4189 children, risk factors for vaccine failure regarding exposure and susceptibility to pertussis have not been studied so far. Pertussis occurred in 346 vaccinated children. Three factors were found to be associated with vaccine failure, independently of the vaccine type, namely the degree of exposure, birth rank, and time since weaning. In the whole-cell vaccine group, the risk of failure increased with birth rank [RR = 2.95 (1.51-5.75)] and was higher in non stunted children [RR = 1.43 (1.05-1.94)]. In the acellular vaccine group, the risk of failure increased with age at exposure to B. pertussis [RR = 2.24 (1.21-4.12) after 18 months of age] and the degree of exposure [RR = 2.14 (1.17-3.93) when the child shared the hut of an index case]. These results highlight the influence of environmental factors on the success of pertussis vaccination. However, they do not explain the shorter duration of protection provided by the acellular vaccine compared to the whole-cell vaccine which persist after controlling and thus might be related to the nature of the vaccine.     

Molecular epidemiology and characterization of plasmid-encoded beta-lactamases produced by Tunisian clinical isolates of Salmonella enterica serotype Mbandaka resistant to broad-spectrum cephalosporins

We studied 31 clinical isolates of Salmonella enterica serotype Mbandaka resistant to broad-spectrum cephalosporins and recovered in Tunisia over a 5-year period. The transferability of this resistance was demonstrated by conjugation experiments. Thirty of the 31 isolates were positive in the double-disk synergy test. By isoelectric focusing analysis, all of the isolates were found to produce a band of beta-lactamase activity with a pI of 5.9. Three of these isolates produced an additional band with a pI of 7.6. PCR and DNA sequencing identified these beta-lactamases as TEM-4 and SHV-2a, respectively. The remaining isolate, highly resistant to ceftazidime but susceptible to cefepime, produced a beta-lactamase that focused at pI 7.8. No synergy was detected by the double-disk synergy test. Sequence analysis of the bla gene amplified by PCR showed that the plasmid-mediated AmpC-type enzyme was ACC-1a. Fingerprinting analysis by repetitive-element PCR and enterobacterial repeat intergenic consensus-PCR suggested that 29 of the 31 Salmonella serotype Mbandaka isolates belonged to the same clonal population.