Cellular and humoral responses to tetanus vaccination in Gabonese children.

Protection to tetanus is often not optimal in developing countries due to incomplete vaccination schemes, or decreased efficacy of vaccination. In this study we investigated the immunological response to tetanus booster vaccination in school children living in a semi-urban or in a rural area of Gabon. Tetanus-specific total IgG as well as antibody subclasses of the IgG1, IgG2, IgG3 and IgG4 isotype and the avidity of the dominating IgG1 subclass were determined both before and 1 month after the booster vaccination. In addition, tetanus-specific cytokine responses were determined. We found a polarization towards a T helper 1 (Th1) profile in the semi-urban children, whereas the cytokine responses of the rural children showed a T helper 2 (Th2) skewed response. Furthermore, tetanus-specific antibodies of the different IgG subclasses were all increased upon a tetanus booster vaccination and levels of IgG1 and IgG3 were higher in the rural children. In conclusion, a tetanus booster vaccination induced a stronger Th2 over Th1 cytokine profile to tetanus toxoid (TT) in rural children who showed the highest levels of IgG1 and IgG3 anti-TT antibody responses.

Cellular and humoral responses to influenza in gabonese children living in rural and semi-urban areas.

BACKGROUND: With the current attention to the pandemic threat of avian influenza viruses, it is recognized that there is little information on influenza in Africa. In addition, the effects of influenza vaccination in African countries could be very different from the effects in regions with less exposure to microorganisms and parasites. METHODS: To monitor the presence of influenza viruses and investigate the immunological responses to influenza vaccination, schoolchildren in semi-urban and rural regions of Gabon were studied. Influenza-specific antibody responses to the 3 strains represented in the vaccine were determined in the serum. Furthermore, cytokine responses were measured after in vitro stimulation of whole blood by influenza antigens, before and after vaccination. RESULTS: Prevaccination titers of antibody against H3N2 were high. At vaccination, the titers of antibody against the 3 influenza strains increased significantly. The anti-H1N1 and anti-B responses after vaccination were weaker in rural schoolchildren than in semi-urban schoolchildren. Influenza-specific cytokine responses were induced within a week, showing significantly lower interferon- gamma and significantly higher interleukin-5 in the children from rural areas. CONCLUSIONS: Prevaccination antibody levels indicated that influenza viruses circulate in Gabon. Altogether, influenza vaccination induces weaker immune responses in a rural population than in a semi-urban population of Gabonese schoolchildren.

Medical informatics in medical research - the Severe Malaria in African Children (SMAC) Network's experience.

OBJECTIVES: Computers are widely used for data management in clinical trials in the developed countries, unlike in developing countries. Dependable systems are vital for data management, and medical decision making in clinical research. Monitoring and evaluation of data management is critical. In this paper we describe database structures and procedures of systems used to implement, coordinate, and sustain data management in Africa. We outline major lessons, challenges and successes achieved, and recommendations to improve medical informatics application in biomedical research in sub-Saharan Africa. METHODS: A consortium of experienced research units at five sites in Africa in studying children with disease formed a new clinical trials network, Severe Malaria in African Children. In December 2000, the network introduced an observational study involving these hospital-based sites. After prototyping, relational database management systems were implemented for data entry and verification, data submission and quality assurance monitoring. RESULTS: Between 2000 and 2005, 25,858 patients were enrolled. Failure to meet data submission deadline and data entry errors correlated positively (correlation coefficient, r = 0.82), with more errors occurring when data was submitted late. Data submission lateness correlated inversely with hospital admissions (r = -0.62). CONCLUSIONS: Developing and sustaining dependable DBMS, ongoing modifications to optimize data management is crucial for clinical studies. Monitoring and communication systems are vital in multi-center networks for good data management. Data timeliness is associated with data quality and hospital admissions.

Lactic acidosis in Gabonese children with severe malaria is unrelated to dehydration.

BACKGROUND: Hyperlactatemia is an important and common complication of severe malaria. We investigated changes in fluid compartment volumes in patients with severe malaria and control patients with the use of bioimpedence analysis. METHODS: We estimated extracellular water and total body water volumes in a total of 180 children: 56 with severe malaria, 94 with moderate malaria, 24 with respiratory tract infection, and 6 with severe diarrhea. RESULTS: There was a mean (+/-SD) decrease in total body water volume of 17+/-24 mL/kg (or 3% of total body water volume) in patients with severe malaria. This compares with a mean (+/-SD) decrease in total body water volume of 33+/-28 mL/kg (or 6% of total body water volume) in patients with severe diarrhea. There was no increase in extracellular water volume in patients with severe malaria, suggesting no significant intravascular volume depletion in patients with severe malaria. There was no relationship between lactatemia and any changes in fluid compartment volumes. CONCLUSIONS: The changes in fluid volumes that were observed are unlikely to be of physiological significance in the pathophysiology of severe malaria.

Reassessment of the resistance of Plasmodium falciparum to chloroquine in Gabon: implications for the validity of tests in vitro vs. in vivo.

Increasing resistance of Plasmodium falciparum to antimalarial drugs presents a major risk factor for people living in endemic areas of tropical Africa. In Lambaréné, Gabon, regular surveillance of chloroquine sensitivity of P. falciparum in vitro has been carried out since 1992 using the WHO standard microtest. Results indicated that from 1994 onwards chloroquine resistance in vitro decreased significantly and that by 2000, about 70% of parasite isolates seemed to be sensitive to chloroquine in vitro. In 2001, we conducted a clinical study to reassess the efficacy of chloroquine in vivo for the treatment of uncomplicated P. falciparum malaria. Twenty-six patients aged 4-15 years were included in this study. Most unexpectedly, the study demonstrated high-grade resistance to chloroquine in vivo (failure rate on day 28 of 100%). As a consequence, tests of parasite susceptibility to chloroquine in vitro were repeated using the same protocol except for the replacement of previously used commercially available predosed WHO culture plates by independently dosed plates. All tested P. falciparum isolates were highly resistant to chloroquine, correlating well with our clinical findings. We concluded that high level resistance of P. falciparum to chloroquine persists in the study area. Neglect or absence of quality controls of essential test material can lead to invalid study results and wrong conclusions and should always be suspected in the case of major fluctuations in the sensitivity patterns of an antimalarial drug in vitro. In addition, our results highlight the supreme value of tests in vivo in providing reliable estimates of the efficacy of an antimalarial in a specific area.

[No influence of season of transmission nor age of patients on the complexity and genetic diversity of Plasmodium falciparum infection in Cotonou, Benin]. / Pas d'influence de la saison de transmission ni de l'âge des patients sur la complexité et la diversité génétique des infections dues a Plasmodium falciparum à Cotonou (Bénin).

The aim of the present study was to determine the genetic diversity and allelic frequencies of the genes encoding for the merozoite surface protein-1 (MSP-1) and protein-2 (MSP-2) of P. falciparum collected from Beninese patients during the high and low transmission seasons in Cotonou, in South Benin. Sixty and twenty-four patients were sampled during the dry and wet seasons, respectively Parasite DNA was analysed using allele-specific primers to amplify block2 of MSP-1 and central variable region of MSP-2. A total of 12 (K1, Mad20, Ro33) MSP-1 and 23 (3D7, FC27 and hybrids) MSP-2 alleles were detected. Neither age nor transmission season modified the genetic diversity of P. falciparum nor the distribution of MSP-1 and MSP-2 alleles. Combining the results of MSP-1 and MSP-2 genotyping, multiple P. falciparum infections were observed in 57% and 70% of isolates during the wet and dry seasons, respectively. The complexity of infections defined as the number of parasite genotype per isolate was 2.4 and it was not affected either by the season or by the age of the host. We conclude that change of season did not influence the permanent turn-over of parasites and the complexity of infections. Data obtained here will serve as a baseline for future studies, such as the impact of malaria control measures on parasite populations, to be conducted in Cotonou.

No influence of the transmission season on genetic diversity and complexity of infections in Plasmodium falciparum isolates from Benin.

The principal goals of the present study were to determine the genetic diversity of the merozoite surface protein-1 (MSP-1) and protein-2 (MSP-2) genes and the complexity of infections in P. falciparum isolates collected from Beninese patients during high and low transmission season at Cotonou, in South Benin. Sixty and twenty-four patients were sampled during dry and wet season respectively. Parasite DNA was analysed using allele-specific primers to amplify block 2 of MSP-1 and central variable region of MSP-2 genes. A total of 12 (K1, Mad20, Ro33) MSP-1 and 13 (3D7 and FC27) MSP-2 alleles were detected in overall samples. Neither influence of age nor transmission season was observed in the genetic diversity of parasites and in the distribution ofMSP-1 and MSP-2 alleles. Combining the results of MSP-1 and MSP-2 genotyping, we observed 57% and 70% of multiple infections during dry and wet season respectively. The complexity of infections 2.4 fragments/individual was not affected either by the season or by the age of the host. We speculate that in an area with perennial transmission, change of season did not influence the permanent turn-over of parasites and the number of parasite genotype per person. Data obtained here will be serve as a baseline for future studies which will carried out at Cotonou to analyse the impact of any malaria control measures on parasite populations.

[Evaluation of a simple and rapid method of Plasmodium falciparum DNA extraction using thick blood smears from Gabonese patients]. / Evaluation d'une méthode simple et rapide d'extraction de l'ADN de Plasmodium falciparum à partir de gouttes épaisses de patients gabonais.

In field-based studies, sometimes it is difficult to collect and store samples. We have evaluated a method of malaria parasite deoxyribonucleic (DNA) extraction from non-stained thick dried blood smears collected from 108 Gabonese patients. This method of DNA isolation was compared to those using phenol/chloroform. Patients parasitemia ranged from 0 to 240,000 parasites/microliter of blood. Both methods of DNA preparation gave similar results. Of the 108 slides, 57% were Plasmodium falciparum positive after PCR analysis of the MSA-2 gene and 34% were positive by microscopical examination. Thirty-six and seventy-two blood smears from patients were also tested after one and four weeks' storage respectively, at room temperature, and the parasite DNA was successfully extracted. We conclude that this simple method of collection and rapid procedure of parasite DNA isolation are adequate and convenient in the field when a large number of samples are required and in the case of repetitive samplings of patients.