Question

A person with sickle cell anemia is

• A. more prone to typhoid
• B. more prone to malaria
• C. less prone to malaria
• D. less prone to typhoid
  

Answer 1

The correct option is C less prone to malaria

Sickle cell anaemia:

Sickle cell anaemia is characterised by the presence of defective haemoglobin molecules due to point mutation in the $H{b}^A$ allele.

The mutant allele, represented by $H{b}^S$, results in altered amino acid (Glutamic acid by Valine at the sixth position) in the beta globin chain of haemoglobin.

Under low oxygen tension, the mutant haemoglobin molecule undergoes polymerisation resulting in the transformation of RBCs into rigid and sickle-shape. These RBCs clog the blood vessels as well as limit oxygen supply to the tissues.

SCA patients: Resistant to malaria :

The malarial parasite, Plasmodium sp., is an intra-erythrocytic parasite. It is unable to multiply in sickle-shaped RBCs.
The sickle cells have membranes which are stretched because of their unusual shape. This membrane becomes porous and leaks nutrients that the parasites need to survive. The faulty cells get destroyed fast along with the parasites.

This makes the heterozygous sickle cell anaemic persons (carriers) resistant to malaria.

Typhoid:

Typhoid caused by Salmonella typhi causes stomach pain, diarrhoea etc.

Salmonella does not transform RBCs into crescent-shaped structures.

Final answer c. less prone to malaria