Which statement is true regarding the development of pyrimethamine resistance in malaria parasites?

• A. Resistance is primarily caused by the acquisition of plasmids from bacteria.
• B. Resistance develops when malaria parasites increase their cell wall thickness.
• C. Resistance arises due to point mutations in the dihydrofolate reductase (dhfr) gene.
• D. Resistance is due to the overproduction of pyrimethamine by the parasite.

Answer: (C)

Verified step by step guidance

1. Understand the mechanism of action of pyrimethamine: it inhibits the enzyme dihydrofolate reductase (DHFR) in malaria parasites, which is essential for folate synthesis and DNA replication.
2. Recognize that resistance to pyrimethamine typically arises through genetic changes in the parasite that reduce the drug's effectiveness.
3. Identify that plasmid acquisition is common in bacteria but not a mechanism for resistance in malaria parasites, which are eukaryotic protozoa.
4. Know that increasing cell wall thickness is not a known resistance mechanism for pyrimethamine in malaria parasites.
5. Focus on the fact that point mutations in the dhfr gene alter the enzyme's structure, decreasing pyrimethamine binding and leading to drug resistance.