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Malaria
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Protective
Effect of Sickle Cell Trait Against Malaria- Associated Mortality
And Morbidity
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It is well known that only in some individuals malaria episodes
progress to severe life-threatening disease, while in the majority
the episodes are self-limiting. This is partly because of the host
genetic factors such as sickle cell gene.
Sickle cell gene is caused by a single amino acid mutation (valine
instead of glutamate at the 6th position) in the beta chain of hemoglobin
gene. Inheritance of this mutated gene from both parents leads to
sickle cell disease and people with this disease have shorter life
expectancy. On the contrary, individuals who are carriers for the
sickle cell disease (with one sickle gene and one normal hemoglobin
gene, also known as sickle cell trait) have some protective advantage
against malaria. As a result, the frequencies of sickle cell carriers
are high in malaria endemic areas.
Most of the earlier studies that have addressed the relationship between
sickle cell trait and malaria were cross sectional and therefore some
important data relevant to the protective effects of sickle cell trait
were missing. Our birth cohort studies (Asembo Bay Cohort Project in
western Kenya ) conducted in collaboration with the Kenya Medical Research
Institute allowed us to investigate this issue in depth. This study
allowed us to determine that sickle cell trait provides 60% protection
against overall mortality and most of this protection occurs between
2-16 months of life before the on set of clinical immunity in areas
with intense transmission of malaria.
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Graph of survival curves ("survival function estimates") of children
HbAA, HbAS or HbSS. Those who were HbAS had a slight survival advantage
over HbAA, with HbSS faring the worst. Sickle cell trait confers protection
against mortality between 2-16 months of life in western Kenya.
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Related Sources: Protective Effects of the Sickle Cell Gene Against Malaria
Morbidity and Mortality. Aidoo M, Terlouw DJ, Kolczak MS, McElroy PD,
ter Kuile FO, Kariuki S, Nahlen BL, Lal AA, Udhayakumar V. Lancet 2002;
359:1311-1312.
Page last modified : April 23, 2004
Content source: Division of Parasitic Diseases
National Center for Zoonotic, Vector-Borne, and Enteric Diseases (ZVED)
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