Sickle Cell Trait - Association With Malaria

Association With Malaria

Sickle cell trait provides a survival advantage over people with normal hemoglobin in regions where malaria is endemic. The trait is known to cause significantly fewer deaths due to malaria, especially when Plasmodium falciparum is the causative organism. This is a prime example of natural selection, evident by the fact that the geographical distribution of the gene (for hemoglobin S) and the distribution of malaria in Africa virtually overlap. Because of the unique survival advantage, people with the trait increase in number as more people infected with malaria and having the normal hemoglobin tend to succumb to the complications.

Although the precise mechanism for this phenomenon is not known, a several factors are believed to be responsible.

• Infected erythrocytes (Red Blood cells) tend to have lower oxygen tension, because it is significantly reduced by the parasite. This causes sickling of that particular erythrocyte, signalling the phagocytes to get rid of the cell and hence the parasite within.
• Since the sickling of parasite infected cells is higher, these selectively get removed by the reticulo-endothelial system, thus sparing the normal erythrocytes.
• Excessive vacuole formation occurs in those parasites infecting sickle cells.
• Sickle trait erythrocytes produce higher levels of the superoxide anion and hydrogen peroxide than do normal erythrocytes, both are toxic to malarial parasites.

The sickle cell trait was found to be 50% protective against mild clinical malaria, 75% protective against admission to the hospital for malaria, and almost 90% protective against severe or complicated malaria.