Moses Laman

Reappraisal of known malaria resistance loci in a large multicenter study

Many human genetic associations with resistance to malaria have been reported, but few have been reliably replicated. We collected data on 11,890 cases of severe malaria due to Plasmodium falciparum and 17,441 controls from 12 locations in Africa, Asia and Oceania. We tested 55 SNPs in 27 loci previously reported to associate with severe malaria. There was evidence of association at P < 1 × 10−4 with the HBB, ABO, ATP2B4, G6PD and CD40LG loci, but previously reported associations at 22 other loci did not replicate in the multicenter analysis. The large sample size made it possible to identify authentic genetic effects that are heterogeneous across populations or phenotypes, with a striking example being the main African form of G6PD deficiency, which reduced the risk of cerebral malaria but increased the risk of severe malarial anemia. The finding that G6PD deficiency has opposing effects on different fatal complications of P. falciparum infection indicates that the evolutionary origins of this common human genetic disorder are more complex than previously supposed.

Features and Prognosis of Severe Malaria Caused by Plasmodium falciparum, Plasmodium vivax and Mixed Plasmodium Species in Papua New Guinean Children

Background Mortality from severe pediatric falciparum malaria appears low in Oceania but Plasmodium vivax is increasingly recognized as a cause of complications and death. The features and prognosis of mixed Plasmodium species infections are poorly characterized. Detailed prospective studies that include accurate malaria diagnosis and detection of co-morbidities are lacking. Methods and Findings We followed 340 Papua New Guinean (PNG) children with PCR-confirmed severe malaria (77.1% P. falciparum, 7.9% P. vivax, 14.7% P. falciparum/vivax) hospitalized over a 3-year period. Bacterial cultures were performed to identify co-incident sepsis. Clinical management was under national guidelines. Of 262 children with severe falciparum malaria, 30.9%, 24.8% and 23.2% had impaired consciousness, severe anemia, and metabolic acidosis/hyperlactatemia, respectively. Two (0.8%) presented with hypoglycemia, seven (2.7%) were discharged with neurologic impairment, and one child died (0.4%). The 27 severe vivax malaria cases presented with similar phenotypic features to the falciparum malaria cases but respiratory distress was five times more common (P = 0.001); one child died (3.7%). The 50 children with P. falciparum/vivax infections shared phenotypic features of mono-species infections, but were more likely to present in deep coma and had the highest mortality (8.0%; P = 0.003 vs falciparum malaria). Overall, bacterial cultures were positive in only two non-fatal cases. 83.6% of the children had alpha-thalassemia trait and seven with coma/impaired consciousness had South Asian ovalocytosis (SAO). Conclusions The low mortality from severe falciparum malaria in PNG children may reflect protective genetic factors other than alpha-thalassemia trait/SAO, good nutrition, and/or infrequent co-incident sepsis. Severe vivax malaria had similar features but severe P. falciparum/vivax infections were associated with the most severe phenotype and worst prognosis.

Reduced Risk of Plasmodium vivax Malaria in Papua New Guinean Children with Southeast Asian Ovalocytosis in Two Cohorts and a Case-Control Study

Ivo Mueller and colleagues examined the association of Southeast Asian ovalocytosis with Plasmodium vivax infection by genotyping 1975 children enrolled in three independent epidemiological studies conducted in the Madang area of Papua New Guinea and assessing P. vivax infection and disease in the children.

Population genomics studies identify signatures of global dispersal and drug resistance in Plasmodium vivax

Plasmodium vivax is a major public health burden, responsible for the majority of malaria infections outside Africa. We explored the impact of demographic history and selective pressures on the P. vivax genome by sequencing 182 clinical isolates sampled from 11 countries across the globe, using hybrid selection to overcome human DNA contamination. We confirmed previous reports of high genomic diversity in P. vivax relative to the more virulent Plasmodium falciparum species; regional populations of P. vivax exhibited greater diversity than the global P. falciparum population, indicating a large and/or stable population. Signals of natural selection suggest that P. vivax is evolving in response to antimalarial drugs and is adapting to regional differences in the human host and the mosquito vector. These findings underline the variable epidemiology of this parasite species and highlight the breadth of approaches that may be required to eliminate P. vivax globally.

Severe anemia in Papua New Guinean children from a malaria-endemic area: a case-control etiologic study.

Background There are few detailed etiologic studies of severe anemia in children from malaria-endemic areas and none in those countries with holoendemic transmission of multiple Plasmodium species. Methodology/Principal Findings We examined associates of severe anemia in 143 well-characterized Papua New Guinean (PNG) children aged 0.5–10 years with hemoglobin concentration <50 g/L (median [inter-quartile range] 39 [33]–[44] g/L) and 120 matched healthy children (113 [107–119] g/L) in a case-control cross-sectional study. A range of socio-demographic, behavioural, anthropometric, clinical and laboratory (including genetic) variables were incorporated in multivariate models with severe anemia as dependent variable. Consistent with a likely trophic effect of chloroquine or amodiaquine on parvovirus B19 (B19V) replication, B19V PCR/IgM positivity had the highest odds ratio (95% confidence interval) of 75.8 (15.4–526), followed by P. falciparum infection (19.4 (6.7–62.6)), vitamin A deficiency (13.5 (5.4–37.7)), body mass index-for-age z-score <2.0 (8.4 (2.7–27.0)) and incomplete vaccination (2.94 (1.3–7.2)). P. vivax infection was inversely associated (0.12 (0.02–0.47), reflecting early acquisition of immunity and/or a lack of reticulocytes for parasite invasion. After imputation of missing data, iron deficiency was a weak positive predictor (6.4% of population attributable risk). Conclusions/Significance These data show that severe anemia is multifactorial in PNG children, strongly associated with under-nutrition and certain common infections, and potentially preventable through vitamin A supplementation and improved nutrition, completion of vaccination schedules, and intermittent preventive antimalarial treatment using non-chloroquine/amodiaquine-based regimens.

γδ T cells and CD14+ monocytes are predominant cellular sources of cytokines and chemokines associated with severe malaria

BACKGROUND Severe malaria (SM) is associated with high levels of cytokines such as tumor necrosis factor (TNF), interleukin 1 (IL-1), and interleukin 6 (IL-6). The role of chemokines is less clear, as is their cellular source. METHODS In a case-control study of children with SM (n = 200), uncomplicated malaria (UM) (n = 153) and healthy community controls (HC) (n = 162) in Papua, New Guinea, we measured cytokine/chemokine production by peripheral blood mononuclear cells (PBMCs) stimulated with live Plasmodium falciparum parasitized red blood cells (pRBC). Cellular sources were determined. Associations between immunological endpoints and clinical/parasitological variables were tested. RESULTS Compared to HC and UM, children with SM produced significantly higher IL-10, IP-10, MIP-1βm and MCP-2. TNF and MIP-1α were significantly higher in the SM compared to the UM group. IL-10, IL-6, MIP-1α, MIP-1β, and MCP-2 were associated with increased odds of SM. SM syndromes were associated with distinct cytokine/chemokine response profiles compared to UM cases. TNF, MIP-1β, and MIP-1α were produced predominantly by monocytes and γδ T cells, and IL-10 by CD4(+) T cells. CONCLUSIONS Early/innate PBMC responses to pRBC in vitro are informative as to cytokines/chemokines associated with SM. Predominant cellular sources are monocytes and γδ T cells. Monocyte-derived chemokines support a role for monocyte infiltrates in the etiology of SM.

Lumbar Puncture in Children from an Area of Malaria Endemicity Who Present with a Febrile Seizure

BACKGROUND Although routine lumbar puncture (LP) is often recommended as part of the assessment of fever-associated seizures in children, accumulating evidence questions its value and reveals a decrease in its frequency. Our primary hypothesis was that children who present with a single seizure but with no clinical signs of meningism or coma do not require LP as part of initial diagnostic assessment. METHODS We prospectively followed up 377 children aged 2 months through 10 years who presented with at least 1 fever-associated seizure to Modilon Hospital, Madang, Papua New Guinea, from November 2007 through July 2009. Clinical management was performed by hospital staff according to national pediatric guidelines. RESULTS Of 188 children with a single seizure and 189 children with multiple seizures, 139 (73.9%) and 154 (81.5%), respectively, underwent a LP as part of their initial assessment. Of the 130 children with a single seizure but no evidence of meningism (ie, neck stiffness, positive Kernigs or Brudzinskis sign, and bulging fontanelle) or coma (Blantyre Coma Score 2), none (95% confidence interval, 0%-3.6%) had proven or probable acute bacterial meningitis, and only 1 patient had viral encephalitis (subacute sclerosing panencephalitis). Eighty-one of these children (62.3%) had a final diagnosis of a simple febrile seizure. Proven or probable acute bacterial meningitis was more common in children with a single seizure and meningism or coma (10; 17.2%) and in those with multiple seizures without or with meningism or coma (2 [2.0%] and 30 [33.7%], respectively). CONCLUSIONS Initial LP is unnecessary when careful clinical assessment indicates features of a simple febrile seizure.

Plasma Plasmodium falciparum histidine-rich protein-2 concentrations do not reflect severity of malaria in Papua New Guinean children

BACKGROUND In areas of unstable malaria transmission, plasma Plasmodium falciparum histidine-rich protein 2 (PfHRP-2) concentrations parallel total parasite biomass and thus infection severity. However, where transmission is more intense, plasma PfHRP-2 might not reliably predict complications and mortality. METHODS As part of a prospective case-control study of severe pediatric illness in Madang, Papua New Guinea, we recruited 220 children aged 6 months to 10 years with severe falciparum malaria, 48 with uncomplicated malaria, and 139 healthy controls. Groups were matched by age, sex, and province of parental birth. Plasma PfHRP-2 levels were quantified by validated immunoassay. RESULTS Detectable plasma PfHRP-2 concentrations were present in 21 healthy controls (15.1%). Although plasma PfHRP-2 levels were higher in the children with clinical malaria (P < .001), there was no difference between those with uncomplicated and severe infections (median, 584 and 456 ng/mL, respectively [interquartile range, 77-1114 and 113-1113 ng/mL, respectively]; P = .43). Log parasitemia, hemoglobin, log plasma bilirubin, and plasma creatinine levels were independently associated with plasma PfHRP-2 levels in multiple regression analysis (P ≤ .014), but coma, blood lactate level, and plasma bicarbonate level were not. The 1 severely ill child who died had a plasma PfHRP-2 concentration of 483 ng/mL, close to the group median. CONCLUSIONS The clinical and prognostic utility of plasma PfHRP-2 concentrations depends on the epidemiologic circumstances. In areas of intense malaria transmission, plasma PfHRP-2 reflects recent as well as present infections.

Characterisation of the opposing effects of G6PD deficiency on cerebral malaria and severe malarial anaemia

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is believed to confer protection against Plasmodium falciparum malaria, but the precise nature of the protective effect has proved difficult to define as G6PD deficiency has multiple allelic variants with different effects in males and females, and it has heterogeneous effects on the clinical outcome of P. falciparum infection. Here we report an analysis of multiple allelic forms of G6PD deficiency in a large multi-centre case-control study of severe malaria, using the WHO classification of G6PD mutations to estimate each individual’s level of enzyme activity from their genotype. Aggregated across all genotypes, we find that increasing levels of G6PD deficiency are associated with decreasing risk of cerebral malaria, but with increased risk of severe malarial anaemia. Models of balancing selection based on these findings indicate that an evolutionary trade-off between different clinical outcomes of P. falciparum infection could have been a major cause of the high levels of G6PD polymorphism seen in human populations. DOI: http://dx.doi.org/10.7554/eLife.15085.001

Comparison of an assumed versus measured leucocyte count in parasite density calculations in Papua New Guinean children with uncomplicated malaria

BackgroundThe accuracy of the World Health Organization method of estimating malaria parasite density from thick blood smears by assuming a white blood cell (WBC) count of 8,000/μL has been questioned in several studies. Since epidemiological investigations, anti-malarial efficacy trials and routine laboratory reporting in Papua New Guinea (PNG) have all relied on this approach, its validity was assessed as part of a trial of artemisinin-based combination therapy, which included blood smear microscopy and automated measurement of leucocyte densities on Days 0, 3 and 7.Results168 children with uncomplicated malaria (median (inter-quartile range) age 44 (39–47) months) were enrolled, 80.3% with Plasmodium falciparum monoinfection, 14.9% with Plasmodium vivax monoinfection, and 4.8% with mixed P. falciparum/P. vivax infection. All responded to allocated therapy and none had a malaria-positive slide on Day 3. Consistent with a median baseline WBC density of 7.3 (6.5-7.8) × 109/L, there was no significant difference in baseline parasite density between the two methods regardless of Plasmodium species. Bland Altman plots showed that, for both species, the mean difference between paired parasite densities calculated from assumed and measured WBC densities was close to zero. At parasite densities <10,000/μL by measured WBC, almost all between-method differences were within the 95% limits of agreement. Above this range, there was increasing scatter but no systematic bias.ConclusionsDiagnostic thresholds and parasite clearance assessment in most PNG children with uncomplicated malaria are relatively robust, but accurate estimates of a higher parasitaemia, as a prognostic index, requires formal WBC measurement.