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Another interesting way malaria cannot be transmitted

There is another “natural” way, or condition which prevents the spreading of Malaria – it is the sickle-cell disease!

Sickle-cell anemia is congenital disease characterized by abnormal blood cells having a crescent shape. This is due to the abnormal hemoglobin called sickle hemoglobin (also known as hemoglobin S.), which causes the change in the cell’s shape. Sickle cells are sticky and not as elastic as normal red blood cells, making their travel through the blood vessels a lot harder. They often block the blood flow, preventing the blood to come to the limbs and organs, which can cause organ damage and pain.

On the molecular level, the difference between the normal and sickle-cell hemoglobin is only in one amino acid. This change occurs in the β-globin chain; namely, hydrophilic glutamic acid on the sixth position gets replaced with hydrophobic valine. It is important to mention that there are actually two mutation sites in the final protein, since mutation happens in one beta subunit, but hemoglobin has two of these (and two alpha subunits).

After the hemoglobin is deoxygenated, a small hydrophobic patch appears on the surface which is a good contact point for more hemoglobin proteins, making them stick together and thus form a chain. This polymerized hemoglobin distorts the normal shape of red blood cells. The condition is not so serious if a patient is heterozygous, having both normal and sickle-cell hemoglobin proteins, since the normal hemoglobin prevents the polymerization of the sickle-cell hemoglobin. The real problem occurs when a person is homozygous, resulting in lysed red blood cells.

There is an interesting „side effect“ of sickle-cell disease, however. Persons with this disease (even heterozygotes) are resistant to one type of malaria. This is due to the fact that malaria parasites attack red blood cells. However, the body senses that sickled cells are defective, and it destroys them by sending them to the spleen (parasites die with them). Moreover, sickle cell is deformed in shape having more pores which leads to the excess leakage of nutrients outside of the cell, making the environment unfriendly for the parasite.

This is an interesting way how one negative thing can result in another positive one.