How does sickle cell trait influence susceptibility to malaria caused by Plasmodium falciparum?

• A. Increases risk of severe malaria
• B. Provides partial protection against severe malaria by altering parasite invasion and growth; carriers have lower risk of severe disease
• C. No effect on malaria susceptibility
• D. Confers complete immunity to malaria

Answer: (B)

Sickle cell trait provides a selective advantage against severe malaria caused by Plasmodium falciparum. When a person carries one copy of the sickle cell gene, their red blood cells are more prone to sickling only under stress, such as low oxygen tensions seen in microcirculation where the parasite lives. This environment makes the parasite’s growth less efficient and also leads to quicker clearance of infected cells by the spleen. As a result, even if infection occurs, the parasite burden tends to be lower and the risk of severe disease, like cerebral malaria or severe anemia, is reduced. That is why the best answer describes partial protection against severe malaria by altering parasite invasion and growth, with carriers having a lower risk of severe disease, rather than complete immunity or no effect. The protection is not absolute, so individuals with sickle cell trait can still contract malaria, but the outcomes are typically milder compared to those without the trait.