10-year longitudinal study of malaria in children: Insights into acquisition and maintenance of naturally acquired immunity

Background: Studies of long-term malaria cohorts have provided essential insights into how Plasmodium falciparum interacts with humans, and influences the development of antimalarial immunity. Immunity to malaria is acquired gradually after multiple infections, some of which present with clinical symptoms. However, there is considerable variation in the number of clinical episodes experienced by children of the same age within the same cohort. Understanding this variation in clinical symptoms and how it relates to the development of naturally acquired immunity is crucial in identifying how and when some children stop experiencing further malaria episodes. Where variability in clinical episodes may result from different rates of acquisition of immunity, or from variable exposure to the parasite. Methods: Using data from a longitudinal cohort of children residing in an area of moderate P. falciparum transmission in Kilifi district, Kenya, we fitted cumulative episode curves as monotonic-increasing splines, to 56 children under surveillance for malaria from the age of 5 to 15. Results: There was large variability in the accumulation of numbers of clinical malaria episodes experienced by the children, despite being of similar age and living in the same general location. One group of children from a particular sub-region of the cohort stopped accumulating clinical malaria episodes earlier than other children in the study. Despite lack of further clinical episodes of malaria, these children had higher asymptomatic parasite densities and higher antibody titres to a panel of P. falciparum blood-stage antigens. Conclusions: This suggests development of clinical immunity rather than lack of exposure to the parasite, and supports the view that this immunity to malaria disease is maintained by a greater exposure to P. falciparum, and thus higher parasite burdens. Our study illustrates the complexity of anti-malaria immunity and underscores the need for analyses which can sufficiently reflect the heterogeneity within endemic populations.

Prevalence of Plasmodium Falciparum among Medical Students with different ABO Groups and Electrophoretic Patterns in a Tertiary Institution in Nnewi, Nigeria

There is evidence that Plasmodium falciparum (Pf) malaria is influenced by ABO blood type but the extent of association is not fully established. Some investigators opinioned that haemoglobin electrophoretic patterns are a factor in susceptibility to Pf infection but there is no consensus on possible association between it and ABO blood group and Hb genotypes. This study was designed to determine the prevalence of Pf among different ABO blood groups and Hb electrophoretic patterns of medical students of a tertiary institution in Nnewi, Nigeria. A total of 80 subjects (41 males and 39 females) aged 18-30 years who reported to the Medical Centre of the institution on account of febrile illness were recruited for the study. Information on age, previous malaria episodes and recent use of prophylaxis were sought. Three milliliters (3ml) of blood were collected into EDTA container for ABO grouping, Hb electrophoresis and blood films for P. falciparum detection and quantification by microscopy. Pf prevalence among the subjects was 47.5% (38/80). Thirty-one (38.75%) of the subjects were of blood group O, 27 (33.75%) group A, 19 (23.75%) blood group B and 3(3.75%) blood group AB. Fifty-two (65%) of the subjects were Hb AA and 28 (35%) AS. No significance difference was seen between malaria episodes and ABO blood groups; Hb electrophoretic patterns; gender and parasite density (p>0.05) respectively. A negative correlation was observed between parasite density and age (r= -0.180, p = 0.109). Pf infection, frequency of infection and parasite load is not influenced by blood group and Hb electrophoretic patterns in our study population.

Household Predictors of Malaria Episode in Northern Uganda: Its Implication for Future Malaria Control

Background: Uses of indoor residual spraying (IRS), long-lasting insecticidal nets (LLINS) and treatment with artemisinin-based combination therapy (ACT) are greatly promoted in northern part of Uganda as mitigating strategies for malaria episodes. Unfortunately, the region still records the highest malaria prevalence of 63%. This study assesses household predicators of malaria in the region and their impact on malaria episodes at the household levels.Methods: A cross-sectional study was conducted in four districts of Gulu, Oyam, Kitgum and Agago covering sixteen villages in northern Uganda. In total, 193 households were surveyed. Data was collected through pre-tested structured questionnaire and systematically coded for analysis using R software.Results:Women headed 58% of the 193 households surveyed. Six hundred and five (605) individuals were declared to have spent the previous night in these households. On average, there were two bed nets per household and 502 (86%) spent the night prior to interview under a bed net. Overall, malaria episodes were strongly related to lack of bed nets or lack of use thereof, and directly linked to the number of individuals in a household. Children were prone to malaria more than adults by a ratio of 2:1. When given a choice between insecticides (IRS) and treated bed nets, 1 in 3 households preferred treated bed nets. At the same time, data suggests that bed nets were perceived unnecessary once IRS was applied. If true, the driving force to spraying insecticides indoor then becomes lack of a bed net. Conclusions:Household predicators of incidence of malaria in northern Uganda includes bed nets, use of treated bed nets, and indoor residual spraying with households not practicing any of these bearing the heaviest burden of malaria. Hierarchical clustering on principal components (HCPC) clusters households into four types in northern Uganda, 1) household that use bed nets and sleep in houses sprayed with insecticides; 2) households that use bed nets but no indoor residual spraying with insecticides; 3) households that have no bed nets and no indoor residual spraying; and 4) test bed nets before use. Malaria incidence was higher in children as compared to the adults.

787Multistate modelling to investigate the impact of recurrent malaria episodes on hospital admissions and mortality

Background Inadequate prevention and treatment of malaria can lead to reinfections and recurrent episodes, and for vivax malaria, further recurrences from the dormant liver stage. This study quantified the impact of recurrent malaria episodes on morbidity and mortality. Methods Routinely collected data were available from 68,381 malaria patients presenting to the primary referral hospital in Papua, Indonesia. A multi-state modelling framework, with Cox regression for transition rates, was employed to determine the risks of re-presentation to hospital, receiving in-patient treatment, and early (≤14 days post treatment)/late death following multiple malaria episodes. Results The risk of re-presentation to hospital increased from 34.7% (95%CI: 34.4%–35.1%) at first episode to 58.6% (57.5%–59.6%) following the third episode. Infection with vivax malaria increased the rate of re-presentation to hospital by 1.48-fold (Hazard Ratio 1.48; 95%CI 1.44–1.51) and late hospital in-patient admission by 1.17-fold (1.11–1.22), compared to falciparum. Falciparum malaria caused a higher overall rate of early death (1.54 (1.25–1.92)), however, after multiple episodes, there was a trend towards a greater rate of early death for vivax infection (1.91 (0.73–4.97)). Conclusions Recurrent episodes of malaria can cause substantial morbidity and mortality, highlighting the importance of prevention and effective treatments for both falciparum and vivax malaria. Key messages To achieve elimination of malaria in South-East Asia, where prevalence of vivax malaria is high, we must prioritise the radical cure of vivax to eliminate the liver-stage of this species that causes relapses of infection.

A High Index of Malaria Suspicion is Necessary for Febrile Episodes in Travellers and Migrants Coming from Endemic Areas

Objectives: We aimed to analyse the likelihood of imported malaria in people with a suggestive clinical picture and its distinctive characteristics in a hospital in the south of Madrid, Spain.Methods: This retrospective study consisted of a review of all medical files of patients with any malaria test registered at Móstoles University Hospital between April 2013 and April 2018. All suspected malaria cases were confirmed by Plasmodium spp. polymerase chain reaction (PCR).Results: Of the 328 patients with suspected malaria (53.7% migrant-travellers; 38.7% visitors; 7.6% travellers), 108 cases were confirmed (101 by P. falciparum), accounting for a 33% positive sample rate. Sixteen cases were diagnosed only by PCR. Patients with malaria, compared to those without, presented predominantly with fever (84% vs 65%), were older (34 vs 24 years), sought medical attention earlier (17d vs 32d), had a greater number of previous malaria episodes (74% vs 60%), lower levels of platelets (110,500µL vs 250,000µL), and higher of bilirubin (0.6mg/dL vs 0.5mg/dL). Severe malaria was present in 13 cases; no deaths were recorded. Malaria diagnosis showed a bimodal distribution with two peaks: June to September and November to January. Conclusion: Malaria is still a common diagnosis among febrile patients coming from the tropics specially among migrant travellers. Fever, thrombocytopenia, and/or high bilirubin levels should raise suspicion for this parasitosis. Prompt diagnosis is crucial to avoid severe cases and deaths. We suggest a proportion around 30% of positive samples as a potential adequate index of suspicion for malaria diagnosis.

IFN-λ4 genetic variants influence clinical malaria episodes in a cohort of Kenyan children

Background Interferon (IFN)- λ4, a type III IFN, production is controlled by a dinucleotide frameshift variant (rs368234815-dG/TT) within the first exon of the IFNL4 gene. Carriers of the IFNL4-dG allele but not the IFNL4-TT allele are able to produce the IFN-λ4 protein. Patients with hepatitis C virus that do not produce the IFN-λ4 protein have higher rates of viral clearance suggesting a potential inhibitory role of IFN-λ4 in liver-tropic infections. Methods In this study, it was investigated whether children infected with Plasmodium falciparum, which has a well-characterized liver stage infection, would be more susceptible to clinical malaria relative to their IFNL4-rs368234815 allele. A cohort of 122 children from a malaria holoendemic region of Kenya was analysed. Episodes of clinical malaria and upper respiratory tract infections (URTIs) were determined using information collected from birth to 2 years of age. The dinucleotide frameshift variant IFNL4-rs368234815-dG/TT was genotyped using a TaqMan assay. Results In this cohort, 33% of the study participants had the dG/dG genotype, 45% had the dG/TT genotype, and 22% had TT/TT genotype. The number and time to first episode of clinical malaria and URTIs with respect to the IFNL4-rs368234815 allele was evaluated. It was found that children that carried the IFNL4-rs368234815-dG allele had an increased number of clinical malaria episodes. In addition, there was a significant association between earlier age of first malaria infection with carriers of the IFNL4-dG allele (p-value: 0.021). Conclusion The results suggest that the ability to produce IFN-λ4 negatively affects host immune protection against P. falciparum malaria in Kenyan children.

10-year longitudinal study of malaria in children: Insights into acquisition and maintenance of naturally acquired immunity

Background: Studies of long-term malaria cohorts have provided essential insights into how Plasmodium falciparum interacts with humans, and influences the development of antimalarial immunity. Immunity to malaria is acquired gradually after multiple infections, some of which present with clinical symptoms. However, there is considerable variation in the number of clinical episodes experienced by children of the same age within the same cohort. Understanding this variation in clinical symptoms and how it relates to the development of naturally acquired immunity is crucial in identifying how and when some children stop experiencing further malaria episodes. Where variability in clinical episodes may result from different rates of acquisition of immunity, or from variable exposure to the parasite. Methods: Using data from a longitudinal cohort of children residing in an area of moderate P. falciparum transmission in Kilifi district, Kenya, we fitted cumulative episode curves as monotonic-increasing splines, to 56 children under surveillance for malaria from the age of 5 to 15. Results: There was large variability in the accumulation of numbers of clinical malaria episodes experienced by the children, despite being of similar age and living in the same general location. One group of children from a particular sub-region of the cohort stopped accumulating clinical malaria episodes earlier than other children in the study. Despite lack of further clinical episodes of malaria, these children had higher asymptomatic parasite densities and higher antibody titres to a panel of P. falciparum blood-stage antigens. Conclusions: This suggests development of clinical immunity rather than lack of exposure to the parasite, and supports the view that this immunity to malaria disease is maintained by a greater exposure to P. falciparum, and thus higher parasite burdens. Our study illustrates the complexity of anti-malaria immunity and underscores the need for analyses which can sufficiently reflect the heterogeneity within endemic populations.

Immunoglobulin G responses to variant forms of Plasmodium vivax merozoite surface protein 9 upon natural infection in Thailand

Merozoite surface protein 9 (MSP9) constitutes a ligand complex involved in erythrocyte invasion by malarial merozoites and is a promising vaccine target. Plasmodium vivax MSP9 (PvMSP9) is immunogenic upon natural malaria exposure. To address whether sequence diversity in PvMSP9 among field isolates could affect natural antibody responses, the recombinant proteins representing two variants each for the N- and the C-terminal domains of PvMSP-9 were used as antigens to assess antibody reactivity among 246 P. vivax-infected patients’ sera from Tak and Ubon Ratchathani Provinces in Thailand. Results revealed that the seropositivity rates of IgG antibodies to the N-terminal antigens were higher than those to the C-terminal antigens (87.80% vs. 67.48%). Most seropositive sera were reactive to both variants, suggesting the presence of common epitopes. Variant-specific antibodies to the N- and the C-terminal antigens were detected in 15.85% and 16.70% of serum samples, respectively. These seropositivity rates were not significant difference between provinces. The seropositivity rates, levels and avidity of anti-PvMSP9 antibodies exhibited positive trends towards increasing malaria episodes. The IgG isotype responses to the N- and the C-terminal antigens were mainly IgG1 and IgG3. The profile of IgG responses may have implications for development of PvMSP9-based vaccine.

Hepatic safety of repeated treatment with pyronaridine‐artesunate versus artemether–lumefantrine in patients with uncomplicated malaria: a secondary analysis of the WANECAM 1 data from Bobo-Dioulasso, Burkina Faso

Background The use of pyronaridine-artesunate (PA) has been associated with scarce transaminitis in patients. This analysis aimed to evaluate the hepatic safety profile of repeated treatment with PA versus artemether–lumefantrine (AL) in patients with consecutive uncomplicated malaria episodes in Bobo-Dioulasso, Burkina Faso. Methods This study analysed data from a clinical trial conducted from 2012 to 2015, in which participants with uncomplicated malaria were assigned to either PA or AL arms and followed up to 42 days. Subsequent malaria episodes within a 2-years follow up period were also treated with the same ACT initially allocated. Transaminases (AST/ALT), alkaline phosphatase (ALP), total and direct bilirubin were measured at days 0 (baseline), 3, 7, 28 and on some unscheduled days if required. The proportions of non-clinical hepatic adverse events (AEs) following first and repeated treatments with PA and AL were compared within study arms. The association of these AEs with retreatment in each arm was also determined using a logistic regression model. Results A total of 1379 malaria episodes were included in the intention to treat analysis with 60% of all cases occurring in the AL arm. Overall, 179 non-clinical hepatic AEs were recorded in the AL arm versus 145 in the PA arm. Elevated ALT was noted in 3.05% of treated malaria episodes, elevated AST 3.34%, elevated ALP 1.81%, and elevated total and direct bilirubin in 7.90% and 7.40% respectively. Retreated participants were less likely to experience elevated ALT and AST than first episode treated participants in both arms. One case of Hy’s law condition was recorded in a first treated participant of the PA arm. Participants from the retreatment group were 76% and 84% less likely to have elevated ALT and AST, respectively, in the AL arm and 68% less likely to present elevated ALT in the PA arm. In contrast, they were almost 2 times more likely to experience elevated total bilirubin in both arms. Conclusions Pyronaridine-artesunate and artemether–lumefantrine showed similar hepatic safety when used repeatedly in participants with uncomplicated malaria. Pyronaridine-artesunate represents therefore a suitable alternative to the current first line anti-malarial drugs in use in endemic areas. Trial registration Pan African Clinical Trials Registry. PACTR201105000286876

Hepatic safety of repeated treatment with pyronaridine-artesunate versus artemether-lumefantrine in patients with uncomplicated malaria: a secondary analysis of the WANECAM 1 data from Bobo-Dioulasso, Burkina Faso

BackgroundThe use of pyronaridine-artesunate (PA) has been associated with scarce transaminitis in patients. This analysis aimed to evaluate the hepatic safety profile of repeated treatment with PA versus artemether-lumefantrine (AL) in patients with consecutive uncomplicated malaria episodes in Bobo-Dioulasso, Burkina Faso. MethodsThis study analysed data from a clinical trial conducted from 2012 to 2015, in which participants with uncomplicated malaria were assigned to either PA or AL arms and followed up to 42 days. Subsequent malaria episodes within a 2-years follow up period were also treated with the same ACT initially allocated. Transaminases (AST/ALT), alkaline phosphatase (ALP), total and direct bilirubin were measured at days 0 (baseline), 3, 7, 28 and on some unscheduled days if required. The proportions of non-clinical hepatic adverse events (AEs) following first and repeated treatments with PA and AL were compared within study arms. The association of these AEs with retreatment in each arm was also determined using a logistic regression model. ResultsA total of 1379 malaria episodes were included in the intention to treat analysis with 60% of all cases occurring in the AL arm. Overall, 179 non-clinical hepatic AEs were recorded in the AL arm versus 145 in the PA arm. Elevated ALT was noted in 3.05% of treated malaria episodes, elevated AST 3.34%, elevated ALP 1.81%, and elevated total and direct bilirubin in 7.90% and 7.40% respectively. Retreated participants were less likely to experience elevated ALT and AST than first episode treated participants in both arms. One case of Hy’s law condition was recorded in a first treated participant of the PA arm. Participants from the retreatment group were 76% and 84% less likely to have elevated ALT and AST, respectively, in the AL arm and 68% less likely to present elevated ALT in the PA arm. In contrast, they were almost 2 times more likely to experience elevated total bilirubin in both arms.ConclusionPyronaridine-artesunate and artemether-lumefantrine showed similar hepatic safety when used repeatedly in participants with uncomplicated malaria. Pyronaridine-artesunate represents therefore a suitable alternative to the current first line anti-malarial drugs in use in endemic areas.