Malaria Elimination in Africa: Rethinking Strategies for Plasmodium vivax and Lessons from Botswana

The global malaria community has picked up the theme of malaria elimination in more than 90% of the world's population in the next decade. Recent reports of Plasmodium vivax (P. vivax) in sub-Saharan Africa, including in Duffy-negative individuals, threaten the efforts aimed at achieving elimination. This is not only in view of strategies that are tailored only to P. falciparum elimination but also due to currently revealed biological characteristics of P. vivax concerning the relapse patterns of hypnozoites and conservation of large biomasses in cryptic sites in the bone marrow and spleen. A typical scenario was observed in Botswana between 2008 and 2018, which palpably projects how P. vivax could endanger malaria elimination efforts where the two parasites co-exist. The need for the global malaria community, national malaria programs (NMPs), funding agencies and relevant stakeholders to engage in a forum to discuss and recommend clear pathways for elimination of malaria, including P. vivax, in sub-Saharan Africa is warranted.

Children with Plasmodium vivax infection previously observed in Namibia, were Duffy negative and carried a c.136G > A mutation

Background

In a previous study, using a molecular approach, we reported the presence of P. vivax in Namibia. Here, we have extended our investigation to the Duffy antigen genetic profile of individuals of the same cohort with and without Plasmodium infections.

Methods

Participants with P. vivax (n = 3), P. falciparum (n = 23) mono-infections and co-infections of P. vivax/P. falciparum (n = 4), and P. falciparum/P. ovale (n = 3) were selected from seven regions. Participants with similar age but without any Plasmodium infections (n = 47) were also selected from all the regions. Duffy allelic profile was examined using standard PCR followed by sequencing of amplified products. Sequenced samples were also examined for the presence or absence of G125A mutation in codon 42, exon 2.

Results

All individuals tested carried the − 67 T > C mutation. However, while all P. vivax infected participants carried the c.G125A mutation, 7/28 P. falciparum infected participants and 9/41 of uninfected participants did not have the c.G125A mutation. The exon 2 region surrounding codon 42, had a c.136G > A mutation that was present in all P. vivax infections. The odds ratio for lack of this mutation with P. vivax infections was (OR 0.015, 95% CI 0.001–0.176; p = 0.001).

Conclusion

We conclude that P. vivax infections previously reported in Namibia, occurred in Duffy negative participants, carrying the G125A mutation in codon 42. The role of the additional mutation c.136 G > A in exon 2 in P. vivax infections, will require further investigations.

Recent Molecular Assessment of Plasmodium vivax and Plasmodium falciparum Asymptomatic Infections in Botswana

In 2016, we reported the presence of Plasmodium vivax in Botswana through active case detection. A real-time PCR was used during a similar study in 10 districts to assess changes in the P. vivax prevalence. We assessed 1,614 children (2–13 years of age) for hemoglobin (Hb; g/dL) and Plasmodium parasites. The median age of all participants was 5.0 years (25^th percentile, 3 years; 75^th percentile, 8 years). The median Hb (g/dL) level was 12.1, but 18.3% of the participants had anemia (Hb < 11.0 g/dL); these participants were clustered in the younger than 5 years age group in all districts (P < 0.001). The risk of anemia decreased with age 5 years or older (odds ratio [OR], 0.26; 95% confidence interval [CI], 0.197–0.34; P < 0.001). The prevalence rates of Plasmodium parasites were as follows: P. vivax, 12.7%; P. falciparum, 12.7%; P. malariae, 0.74%; and P. ovale (P. ovale curtisi), 0.68%. Mixed infection rates were as follows: P. falciparum and P. vivax, 2.35%; P. falciparum and P. ovale curtisi, 0.56%; P. vivax and P. malariae, 0.06%; and P. falciparum and P. malariae, 0.68%. The infections were largely asymptomatic (99.6%). Using logistic regression, the risk of infection with P. vivax was highest in Kweneng East (OR, 6.2; 95% CI, 2.9–13.1), followed by South East (OR, 5.6; 95% CI, 2.5–12.3) and Ngami (OR, 5.1; 95% CI, 2.2–12.0). Compared to the risk of infection for children younger than 5 years, the risk of infection decreased for children 5 years or older in regions with high rates of P. vivax and P. falciparum infections. P. vivax and P. falciparum have expanded within the asymptomatic population in Botswana; therefore, careful attention is required for their elimination.

Glucose-6-phosphate dehydrogenase deficiency genotypes and allele frequencies in the Kavango and Zambezi regions of northern Namibia

BACKGROUND

Namibia has made significant gains in the fight against malaria, with a target of elimination by 2023. We examined the genotype and allele frequencies of glucose-6-phosphate dehydrogenase (G6PD) deficiency to inform decisions on primaquine use, as we recently detected clusters of Plasmodium ovale curtisi in Kavango.

METHODS

A multistaged cross-sectional sampling method was used to enrol 212 children 2-9 y of age from schools and clinics in the Okavango and Zambezi regions of northern Namibia. Genotypes for the 202 G→A and 376 A→G mutations were assigned by polymerase chain reaction restriction fragment length polymorphism.

RESULTS

Of the 212 subjects enrolled, genotypes were available for 210, made up of 61 males and 149 females. G6PD-deficient males (hemizygotes) and females (homozygotes) constituted 3.27% (2/61) and 0.0% (0/149), respectively. Female heterozygotes (AA- and BA-) constituted 10.07% (15/149), while G6PD wild-type males (with A or B haplotype) and females (with AA, BB or AB haplotypes) consisted of 96.72% (59/61) and 89.93% (134/149), respectively. The A-, A and B allele frequencies were 0.0474, 0.3036 and 0.6490, respectively. Hardy-Weinberg equilibrium tests for female genotype frequencies did not show deviation (p=0.29).

CONCLUSIONS

The frequency of G6PD deficiency alleles in males in the Kavango and Zambezi regions of northern Namibia constitute 3.27%, a first report to inform policy on primaquine role out.

Pregnancy-induced Cardiovascular Pathologies: Importance of Structural Components and Lipids

Pregnancy leads to adaptations for maternal and fetal energy needs. The cardiovascular system bears the brunt of the adaptations as the heart and vessels enable nutrient supply to maternal organs facilitated by the placenta to the fetus. The components of the cardiovascular system are critical in the balance between maternal homeostatic and fetus driven homeorhetic regulation. Since lipids intersect maternal cardiovascular function and fetal needs with growth and in stress, factors affecting lipid deposition and mobilization impact risk outcomes. Here, the cardiovascular components and functional derangements associated with cardiovascular pathology in pregnancy, vis-à-vis lipid deposition, mobilization and maternal and/or cardiac and fetal energy needs are detailed. Most reports on the components and associated pathology in pregnancy, are on derangements affecting the extracellular matrix and epicardial fat, followed by the endothelium, vascular smooth muscle, pericytes and myocytes. Targeted studies on all cardiovascular components and pathological outcomes in pregnancy will enhance targeted interventions.

Prevalence of G6PD deficiency and associated haematological parameters in children from Botswana

Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency is commonly seen in malaria endemic areas as it is known to confer a selective advantage against malaria. Recently, we reported a high proportion of asymptomatic reservoir of Plasmodium vivax in Botswana, that calls for intervention with primaquine to achieve radical cure of vivax malaria. Considering that individuals with this enzyme deficiency are at risk of haemolysis following primaquine treatment, assessment of the population for the relative frequency of G6PD deficiency is imperative. Samples from 3019 children from all the districts of Botswana were successfully genotyped for polymorphisms at positions 202 and 376 of the G6PD gene. Haematological parameters were also measured. The overall population allele frequency (based on the hemizygous male frequency) was 2.30% (95% CI, 1.77-2.83), while the overall frequency of G6PD-deficient genotypes A- (hemizygote and homozygote genotypes only) was 1.26% (95% CI, 0.86-1.66). G6PD deficiency is spread in Botswana according to the historical prevalence of malaria with a North-West to South-East decreasing gradient trend. There was no association between G6PD status and P. vivax infection. G6PD A- form was found to be associated with decreased RBC count and haemoglobin levels without a known cause or illness. In conclusion, we report for the first time the prevalence of G6PD deficiency in Botswana which is relevant for strategies in the malaria elimination campaign. Further work to examine the activities of the enzyme in the Botswana population at risk for malaria is warranted.

Molecular evidence of high rates of asymptomatic P. vivax infection and very low P. falciparum malaria in Botswana

BACKGROUND

Botswana is one of eight SADC countries targeting malaria elimination by 2018. Through spirited upscaling of control activities and passive surveillance, significant reductions in case incidence of Plasmodium falciparum (0.96 - 0.01) was achieved between 2008 and 2012. As part of the elimination campaign, active detection of asymptomatic Plasmodium species by a highly sensitive method was deemed necessary. This study was carried out to determine asymptomatic Plasmodium species carriage by nested PCR in the country, in 2012.

METHOD

A cross-sectional study involving 3924 apparently healthy participants were screened for Plasmodium species in 14 districts (5 endemic: Okavango, Ngami, Tutume, Boteti and Bobirwa; and 9 epidemic: North East, Francistown, Serowe-Palapye, Ghanzi, Kweneng West, Kweneng East, Kgatleng, South East, and Good Hope). Venous blood was taken from each participant for a nested PCR detection of Plasmodium species.

RESULTS

The parasite rates of asymptomatic Plasmodium species detected were as follows: Plasmodium falciparum, 0.16 %; Plasmodium vivax, 4.66 %; Plasmodium malariae, (Pm) 0.16 %; Plasmodium ovale, 0 %, mixed infections (P. falciparum and P. vivax), 0.055 %; and (P. vivax and P. malariae), 0.027 %, (total: 5.062 %). The high proportion of asymptomatic reservoir of P. vivax was clustered in the East, South Eastern and Central districts of the country. There appeared to be a correlation between the occurrence of P. malariae infection with P. vivax infection, with the former only occurring in districts that had substantial P. vivax circulation. The median age among 2-12 year olds for P. vivax infection was 5 years (Mean 5.13 years, interquartile range 3-7 years). The odds of being infected with P. vivax decreased by 7 % for each year increase in age (OR 0.93, 95 % CI 0.87-1.00, p = 0.056).

CONCLUSION

We have confirmed low parasite rate of asymptomatic Plasmodium species in Botswana, with the exception of P.vivax which was unexpectedly high. This has implication for the elimination campaign so a follow up study is warranted to inform decisions on new strategies that take this evidence into account in the elimination campaign.

Hypoglycaemia in an infant of a mother with fasting hyperglycaemia - a case report

SummaryWe report a case of perinatal death from hypoglycaemia in an infant of a mother who had fasting hyperglycaemia diagnosed at 31 weeks of gestation and managed with diet alone. Blood glucose values were not conclusive of gestational impaired glucose tolerance by WHO and American Diabetes Association standards, yet autopsy histological findings in the pancreas were similar to that described in neonates of a diabetic mother. We therefore emphasize that all pregnant women with inconclusive glucose values for diagnosis of full blown gestational diabetes mellitus should be fully investigated and closely monitored during antenatal care. The infants of such mothers may be at a higher risk of hypoglycemia in the immediate post natal period and would require similar monitoring and aggressive management.