Malaria and Early African Development: Evidence from the Sickle Cell Trait (original) (raw)
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Malaria continues to select for sickle cell trait in Central Africa
Proceedings of the National Academy of Sciences, 2015
Sickle cell disease (SCD) is a genetic disorder that poses a serious health threat in tropical Africa, which the World Health Organization has declared a public health priority. Its persistence in human populations has been attributed to the resistance it provides to Plasmodium falciparum malaria in its heterozygous state, called sickle cell trait (SCT). Because of migration, SCT is becoming common outside tropical countries: It is now the most important genetic disorder in France, affecting one birth for every 2,400, and one of the most common in the United States. We assess the strength of the association between SCT and malaria, using current data for both SCT and malaria infections. A total of 3,959 blood samples from 195 villages distributed over the entire Republic of Gabon were analyzed. Hemoglobin variants were identified by using HPLCy (HPLC). Infections by three species of Plasmodium were detected by PCR followed by sequencing of a 201-bp fragment of cytochrome b. An increase of 10% in P. falciparum malaria prevalence is associated with an increase by 4.3% of SCT carriers. An increase of 10 y of age is associated with an increase by 5.5% of SCT carriers. Sex is not associated with SCT. These strong associations show that malaria remains a selective factor in current human populations, despite the progress of medicine and the actions undertaken to fight this disease. Our results provide evidence that evolution is still present in humans, although this is sometimes questioned by scientific, political, or religious personalities. sickle cell disease | Plasmodium falciparum | human evolution | Gabon | natural selection
Effect of malaria on the outcomes of sickle cell phenotypes in a semi-nomadic population
Pyramid Journal of Medicine
Studies have shown that malaria contribute significantly to mortality among infants and children with Sickle Cell Anemia (SCA). The nomadic lifestyle of the Fulanis make access to health care difficult and exposure to malaria high. We conducted a cross sectional study among consenting members of a semi-nomadic Fulani population in Nigeria to determine the impact of malaria on the outcome of SCA. On-the-spot malaria rapid diagnostic test (RDT) and hemoglobin electrophoresis were done. A total of 229 subjects participated, 100 (43.7%) females. Median age was 35 years (yrs) with range of 15-80 yrs. Hemoglobin AS phenotype was found among 53 (23.1%) subjects; none had hemoglobin SS. A positive malaria RDT was found among 24 (10.5%) individuals. The FGD revealed that majority of the respondents considered malaria as an important cause of ill-health but were not aware of SCA as an important disease. The high prevalences of malaria, hemoglobin AS phenotype, and absent of hemoglobin SS in t...
Sickle Cell Trait and the Risk of Plasmodium falciparum Malaria and Other Childhood Diseases
The Journal of Infectious Diseases, 2005
Background. The gene for sickle hemoglobin (HbS) is a prime example of natural selection. It is generally believed that its current prevalence in many tropical populations reflects selection for the carrier form (sickle cell trait [HbAS]) through a survival advantage against death from malaria. Nevertheless, 150 years after this hypothesis was first proposed, the epidemiological description of the relationships between HbAS, malaria, and other common causes of child mortality remains incomplete. Methods. We studied the incidence of falciparum malaria and other childhood diseases in 2 cohorts of children living on the coast of Kenya. Results. The protective effect of HbAS was remarkably specific for falciparum malaria, having no significant impact on any other disease. HbAS had no effect on the prevalence of symptomless parasitemia but was 50% protective against mild clinical malaria, 75% protective against admission to the hospital for malaria, and almost 90% protective against severe or complicated malaria. The effect of HbAS on episodes of clinical malaria was mirrored in its effect on parasite densities during such episodes. Conclusions. The present data are useful in that they confirm the mechanisms by which HbAS confers protection against malaria and shed light on the relationships between HbAS, malaria, and other childhood diseases. Malaria causes 1200 million episodes of febrile illness and 11 million deaths every year in young children living in sub-Saharan Africa [1, 2]. The factors determining which children die and which survive are complex, but they are likely related to both the host and the parasite. Of the host-specific factors, the sickle cell trait (HbAS) remains the best described [3], having been shown to confer strong protection against Plasmodium falciparum malaria in numerous studies conducted in various countries over the course of 150 years [4-10]; nevertheless, the protective mechanisms at work remain incompletely understood. A number
Long-Term Exposure to Malaria and Development: Disaggregate Evidence for Contemporaneous Africa
Journal of Demographic Economics, 2017
Malaria afflicts mankind since thousands of years and still imposes serious health impediments and considerable mortality on the affected populations. Empirical investigations of the role of malaria for economic development at the country level deliver mixed findings, however. We study the role of long term Malaria exposure on development today using disaggregate within-country variation for the whole of Africa with 1×1 degree cells as units of observation. Local development is measured by light density at night. Based on insights from epidemiology, which documents that genetic and acquired immunities reduce Malaria risk for adults in holoendemic areas, the effect is hypothesized to be non-linear, with a peak for intermediate rather than high exposure to the pathogen. The empirical findings support this hypothesis. The results also suggest the existence of a significant moderating effect of genetic immunities measured by the prevalence of the sickle cell trait in the population.
The indirect health effects of malaria estimated from health advantages of the sickle cell trait
Nature Communications, 2019
Most estimates of the burden of malaria are based on its direct impacts; however, its true burden is likely to be greater because of its wider effects on overall health. Here we estimate the indirect impact of malaria on children's health in a case-control study, using the sickle cell trait (HbAS), a condition associated with a high degree of specific malaria resistance, as a proxy indicator for an effective intervention. We estimate the odds ratios for HbAS among cases (all children admitted to Kilifi County Hospital during 2000-2004) versus community controls. As expected, HbAS protects strongly against malaria admissions (aOR 0.26; 95%CI 0.22-0.31), but it also protects against other syndromes, including neonatal conditions (aOR 0.79; 0.67-0.93), bacteraemia (aOR 0.69; 0.54-0.88) and severe malnutrition (aOR 0.67; 0.55-0.83). The wider health impacts of malaria should be considered when estimating the potential added benefits of effective malaria interventions.
Journal of Integrated Health Sciences, 2017
Sickle cell disease (SCD) though initially restricted to certain geographical places, now has become a global problem due to migration. 1, 2 Epidemiology of SCD is same as malaria, which is considered to be a disease of tropics. World distribution of sickle gene has remained same like that of past and present malaria. 3 Sickle gene is thought to be result of mutation to protect local community from death due to plasmodial disease. 3 Thus, relationship between malaria and genetic disorders like thalassemia, Sickle cell disorder and glucose-6-phosphate dehydrogenase deficiency (G6PD) is an example of interaction of gene with environment. 3,4,5 Mediterranean region, Africa and Asia which has archives of high malaria prevalence is also native for hemoglobinopathies. Migration and resettlement of communities has made SCD, a global problem which is common in America, Australia and Europe, as well. 1 Continent of Africa has high prevalence of malaria as well as SCD. As per WHO, in 2015, 214 million new cases of malaria were reported of which 88% were in Africa. 6 SCD is also very common in Africa, where 3% of newborn are affected and high mortality (50%-90%) is reported among African children with SCD. 7 ,8 In retrospective hospital based study from The Democratic Republic of Congo, Africa, 90 children of malaria with SCD (homozygous) were admitted. This 10 years study concluded that children below 5 years were at higher risk for acute crises due to malaria. They may need blood transfusion and anti-malarial prophylaxis. 9 Evidence are also available to suggest that sickle cell trait (SCT) is giving protection against malaria mortality and morbidity. It also prevents from heavy parasitaemia and severe anemia due to malaria. 10 However, protection offered is not complete. 9 Malaria-endemic countries who have also high prevalence of SCD, should adopt malaria prophylaxis policy especially for children. 3 In Africa, for comprehensive care, screening, prophylaxis, and treatment of SCD is recommended, however large population based study may tell us about estimate of preventable child deaths by interventions policy and its cost benefit advantage. 7 Again guidelines regarding malarial antiprophylaxis need more precision in varied groups like children, pregnant females, diabetics and immune compromised population.