Sicklecell trait provides resistance to malaria

Sicklecell trait provides resistance to malaria:-

The incidence of sicklecell disease coincides with the high incidence of malaria

in tropical areas of the world (particularly among the black Africans).

Sicklecell trait (heterozygous state with about 40% HbS) provides resistance

to malaria which is a major cause of death in tropical areas. This is explained as

follows

1. Malaria is a parasitic disease caused by Plasmodium falciparum in Africa. The

malarial parasite spends a part of its life cycle in erythrocytes. Increased lysis

of sickled cells (shorter life span of erythrocytes) interrupts the parasite cycle.

2. More recent studies indicate that malarial parasite increases the acidity of

erythrocytes (pH down by 0.4). The lowered pH increases the sickling of

erythrocytes to about 40% from the normally occurring 2%. Therefore, the

entry of malarial parasite promotes sickling leading to lysis of erythrocytes.

Furthermore, the concentration of K+ is low in sickled cells which is

unfavourable for the parasite to survive.

Sicklecell trait appears to be an adaptation for the survival of the individuals

in malaria-infested regions. Unfortunately, homozygous individuals, the

patients of sicklecell anemia (much less frequent than the trait), cannot live

beyond 20 years.