Malarial parasites could be best obtained from a patient

The correct option is: few hours after the temperature reaches to normal.

Step-by-Step Explanation:

1. The Erythrocytic Cycle of Plasmodium:
Inside the human host, the malaria-causing parasite (Plasmodium) infects and multiplies within the red blood cells (RBCs). This asexual reproduction cycle is known as erythrocytic schizogony.

2. Cause of Fever and Chills:
The characteristic high fever and shivering (rigor) associated with malaria are triggered when the infected red blood cells rupture simultaneously. This rupture releases a large number of young parasites (merozoites) and toxic metabolic byproducts (such as hemozoin) directly into the patient's bloodstream.

3. Optimal Timing for Parasite Detection:
During the high fever phase, the parasites are mostly free in the blood plasma (extracellular merozoites), where they are rapidly targeted by the host's immune system or are actively invading new RBCs.
A few hours after the body temperature returns to normal, the merozoites have successfully entered new RBCs and developed into stable, growing forms (such as the ring-stage trophozoites). Collecting blood during this post-fever period ensures a high concentration of stable, intracellular parasites in the peripheral blood, making it the best time to obtain and identify them in a diagnostic blood smear.