The prevalence of glucose-6-phosphate dehydrogenase deficiency in Gambian school children.

BACKGROUND: Primaquine, the only available drug effective against Plasmodium falciparum sexual stages, induces also a dose-dependent haemolysis, especially in glucose-6-phosphate dehydrogenase deficient (G6PDd) individuals. Therefore, it is important to determine the prevalence of this deficiency in areas that would potentially benefit from its use. The prevalence of G6PD deficiency by genotype and enzyme activity was determined in healthy school children in The Gambia. METHODS: Blood samples from primary school children collected during a dry season malaria survey were screened for G6PDd and malaria infection. Genotypes for allele mutations reported in the country; 376, 202A-, 968A- and 542 were analysed while enzyme activity (phenotype) was assayed using a semi-quantitative commercial test kit. Enzyme activity values were fitted in a finite mixture model to determine the distribution and calculate a cut-off for deficiency. The association between genotype and phenotype for boys and girls as well as the association between mutant genotype and deficient phenotype was analysed. RESULTS: Samples from 1,437 children; 51% boys were analysed. The prevalence of P. falciparum malaria infection was 14%. The prevalence of the 202A-, 968 and 542 mutations was 1.8%, 2.1% and 1.0%, respectively, and higher in boys than in girls. The prevalence of G6PDd phenotype was 6.4% (92/1,437), 7.8% (57/728) in boys and 4.9% (35/709) in girls with significantly higher odds in the former (OR 1.64, 95% CI 1.05, 2.53, p = 0.026). The deficient phenotype was associated with reduced odds of malaria infection (OR 0.77, 95% CI 0.36, 1.62, p = 0.49). CONCLUSIONS: There is a weak association between genotype and phenotype estimates of G6PDd prevalence. The phenotype expression of deficiency represents combinations of mutant alleles rather than specific mutations. Genotype studies in individuals with a deficient phenotype would help identify alleles responsible for haemolysis.

Detecting Foci of Malaria Transmission with School Surveys: A Pilot Study in the Gambia.

BACKGROUND: In areas of declining malaria transmission such as in The Gambia, the identification of malaria infected individuals becomes increasingly harder. School surveys may be used to identify foci of malaria transmission in the community. METHODS: The survey was carried out in May-June 2011, before the beginning of the malaria transmission season. Thirty two schools in the Upper River Region of The Gambia were selected with probability proportional to size; in each school approximately 100 children were randomly chosen for inclusion in the study. Each child had a finger prick blood sample collected for the determination of antimalarial antibodies by ELISA, malaria infection by microscopy and PCR, and for haemoglobin measurement. In addition, a simple questionnaire on socio-demographic variables and the use of insecticide-treated bed nets was completed. The cut-off for positivity for antimalarial antibodies was obtained using finite mixture models. The clustered nature of the data was taken into account in the analyses. RESULTS: A total of 3,277 children were included in the survey. The mean age was 10 years (SD = 2.7) [range 4-21], with males and females evenly distributed. The prevalence of malaria infection as determined by PCR was 13.6% (426/3124) [95% CI = 12.2-16.3] with marked variation between schools (range 3-25%, p<0.001), while the seroprevalence was 7.8% (234/2994) [95%CI = 6.4-9.8] for MSP119, 11.6% (364/2997) [95%CI = 9.4-14.5] for MSP2, and 20.0% (593/2973) [95% CI = 16.5-23.2) for AMA1. The prevalence of all the three antimalarial antibodies positive was 2.7% (79/2920). CONCLUSIONS: This survey shows that malaria prevalence and seroprevalence before the transmission season were highly heterogeneous.

Prolonged neutrophil dysfunction after Plasmodium falciparum malaria is related to hemolysis and heme oxygenase-1 induction.

It is not known why people are more susceptible to bacterial infections such as nontyphoid Salmonella during and after a malaria infection, but in mice, malarial hemolysis impairs resistance to nontyphoid Salmonella by impairing the neutrophil oxidative burst. This acquired neutrophil dysfunction is a consequence of induction of the cytoprotective, heme-degrading enzyme heme oxygenase-1 (HO-1) in neutrophil progenitors in bone marrow. In this study, we assessed whether neutrophil dysfunction occurs in humans with malaria and how this relates to hemolysis. We evaluated neutrophil function in 58 Gambian children with Plasmodium falciparum malaria [55 (95%) with uncomplicated disease] and examined associations with erythrocyte count, haptoglobin, hemopexin, plasma heme, expression of receptors for heme uptake, and HO-1 induction. Malaria caused the appearance of a dominant population of neutrophils with reduced oxidative burst activity, which gradually normalized over 8 wk of follow-up. The degree of neutrophil impairment correlated significantly with markers of hemolysis and HO-1 induction. HO-1 expression was increased in blood during acute malaria, but at a cellular level HO-1 expression was modulated by changes in surface expression of the haptoglobin receptor (CD163). These findings demonstrate that neutrophil dysfunction occurs in P. falciparum malaria and support the relevance of the mechanistic studies in mice. Furthermore, they suggest the presence of a regulatory pathway to limit HO-1 induction by hemolysis in the context of infection and indicate new targets for therapeutic intervention to abrogate the susceptibility to bacterial infection in the context of hemolysis in humans.

HMOX1 gene promoter alleles and high HO-1 levels are associated with severe malaria in Gambian children.

Heme oxygenase 1 (HO-1) is an essential enzyme induced by heme and multiple stimuli associated with critical illness. In humans, polymorphisms in the HMOX1 gene promoter may influence the magnitude of HO-1 expression. In many diseases including murine malaria, HO-1 induction produces protective anti-inflammatory effects, but observations from patients suggest these may be limited to a narrow range of HO-1 induction, prompting us to investigate the role of HO-1 in malaria infection. In 307 Gambian children with either severe or uncomplicated P. falciparum malaria, we characterized the associations of HMOX1 promoter polymorphisms, HMOX1 mRNA inducibility, HO-1 protein levels in leucocytes (flow cytometry), and plasma (ELISA) with disease severity. The (GT)(n) repeat polymorphism in the HMOX1 promoter was associated with HMOX1 mRNA expression in white blood cells in vitro, and with severe disease and death, while high HO-1 levels were associated with severe disease. Neutrophils were the main HO-1-expressing cells in peripheral blood, and HMOX1 mRNA expression was upregulated by heme-moieties of lysed erythrocytes. We provide mechanistic evidence that induction of HMOX1 expression in neutrophils potentiates the respiratory burst, and propose this may be part of the causal pathway explaining the association between short (GT)(n) repeats and increased disease severity in malaria and other critical illnesses. Our findings suggest a genetic predisposition to higher levels of HO-1 is associated with severe illness, and enhances the neutrophil burst leading to oxidative damage of endothelial cells. These add important information to the discussion about possible therapeutic manipulation of HO-1 in critically ill patients.

Continued decline of malaria in The Gambia with implications for elimination.

BACKGROUND: A substantial decline in malaria was reported to have occurred over several years until 2007 in the western part of The Gambia, encouraging consideration of future elimination in this previously highly endemic region. Scale up of interventions has since increased with support from the Global Fund and other donors. METHODOLOGY/PRINCIPAL FINDINGS: We continued to examine laboratory records at four health facilities previously studied and investigated six additional facilities for a 7 year period, adding data from 243,707 slide examinations, to determine trends throughout the country until the end of 2009. We actively detected infections in a community cohort of 800 children living in rural villages throughout the 2008 malaria season, and assayed serological changes in another rural population between 2006 and 2009. Proportions of malaria positive slides declined significantly at all of the 10 health facilities between 2003 (annual mean across all sites, 38.7%) and 2009 (annual mean, 7.9%). Statistical modelling of trends confirmed significant seasonality and decline over time at each facility. Slide positivity was lowest in 2009 at all sites, except two where lowest levels were observed in 2006. Mapping households of cases presenting at the latter sites in 2007-2009 indicated that these were not restricted to a few residual foci. Only 2.8% (22/800) of a rural cohort of children had a malaria episode in the 2008 season, and there was substantial serological decline between 2006 and 2009 in a separate rural area. CONCLUSIONS: Malaria has continued to decline in The Gambia, as indicated by a downward trend in slide positivity at health facilities, and unprecedented low incidence and seroprevalence in community surveys. We recommend intensification of control interventions for several years to further reduce incidence, prior to considering an elimination programme.

An update of malaria infection and anaemia in adults in Buea, Cameroon.

BACKGROUND: Anaemia is caused by many factors in developing countries including malaria. We compared anaemia rates in patients with malaria parasitaemia to that of patients without malaria parasitaemia. FINDINGS: A cross-sectional study was carried out from November 2007 to July 2008 in health units in Buea, Cameroon. Adult patients with fever or history of fever were included in the study. Information on socio-demographic variables and other variables was collected using a questionnaire. Malaria parasitaemia status was determined by microscopy using Giemsa stained thick blood smears. Haemoglobin levels were determined by the microhaematocrit technique.The study population consisted of 250 adult patients with a mean age of 29.31 years (SD = 10.63) and 59.44% were females. 25.60% of the patients had malaria parasitaemia while 14.80% had anaemia (haemoglobin < 11 g/dl). Logistic regression revealed that those with malaria parasitaemia had more anaemia compared to those without malaria parasitaemia(OR = 4.33, 95%CI = 1.21-15.43, p = 0.02) after adjusting for age, sex, rural residence, socioeconomic status, use of antimalarials, use of insecticide treated nets(ITN) and white blood cell count. CONCLUSIONS: In adult patients with fever in this setting, malaria parasitaemia contributes to anaemia and is of public health impact. Our results also provide a baseline prevalence for malaria parasitaemia in febrile adults in health units in this setting.