Question

The infectious stage of Plasmodium that enters the human body is

• A. trophozoites
• B. sporozoites
• C. female gametocytes
• D. male gametocytes

Answer 1

The correct option is B sporozoites

Malarial protozoa enter the bloodstream of humans through the bite of an infected female Anopheles mosquito. The infective stage is called sporozoites.

Sporozoites travel to the hepatic cells through the bloodstream. In the liver cells (hepatic cells) sporozoites undergo asexual division and mature into merozoites. Merozoite released from the liver cells penetrates erythrocytes. Inside the erythrocytes, these merozoites develop , enlarge and grow . They are termed as trophozoites. The trophozoites undergo asexual reproduction to produced schizonts, which eventually divides to produced merozoites which are released upon erythrocytes lysis. The released merozoites infect other erythrocytes and this cycle repeats after every 48 to 72 hours depending upon the species of Plasmodium involved. Occasionally, merozoites differentiate into microgametocytes and macrogametocytes.

When these erythrocytes containing macro and microgametocytes are ingested by female Anopheles mosquitoes, they develop into female and male gametes. While in the mosquito’s stomach, the microgametes penetrate the macrogametes generating zygotes. The zygotes in turn become motile and elongated (ookinetes). Ookinete migrates to the mosquito gut wall and penetrates and forms an oocyst. Oocyst undergoes meiosis and forms sporozoites which migrate to the salivary gland of mosquitoes. When a mosquito feeds on another host, it transfers fresh sporozoites along with saliva.