Q.Describe the life cycle of the malarial parasite Plasmodium in the human body and in the female Anopheles mosquito, and explain how this cycle produces the periodic fever seen in malaria patients.
The life cycle of Plasmodium alternates between a human host and the female Anopheles mosquito, and it is this alternating cycle that explains the periodic fever of malaria.
In the mosquito: when a female Anopheles mosquito bites an infected person, it ingests Plasmodium forms present in that person's blood. Inside the mosquito's gut, the parasite develops further and eventually migrates to the mosquito's salivary glands, ready to be transmitted at the mosquito's next bite.
Entry into the human body: when this infected mosquito bites a new, healthy person, it injects infective parasite forms along with its saliva into the person's bloodstream.
Multiplication in the human body: the parasites first travel to the liver, where they multiply, before entering the bloodstream and invading red blood cells. Once inside a red blood cell, the parasite multiplies further, using the cell's own contents.
Periodic rupture and fever: eventually, large numbers of infected red blood cells rupture together, releasing newly formed parasites — along with a toxic pigment called haemozoin — into the bloodstream. This sudden release triggers the sharp bout of high fever, chills, and shivering (rigor) that is the hallmark symptom of malaria. Because each Plasmodium species completes its cycle inside red blood cells on a fairly fixed schedule, this rupture recurs periodically — classically every 48 hours for some species, 72 hours for others — producing the disease's characteristic periodic fever pattern.
Completing the cycle: if another Anopheles mosquito bites this now-infected person, it can ingest fresh parasite forms from the person's blood and carry the infection onward to its next victim, continuing the cycle indefinitely unless it is interrupted by prevention or treatment.
An infected female Anopheles mosquito transmits Plasmodium into a human, where it multiplies first in the liver and then inside red blood cells; the periodic, synchronised rupture of infected red blood cells releases the parasite and toxins into the blood, directly causing malaria's recurring fever and chills (roughly every 48-72 hours). A new mosquito biting this infected person ingests the parasite and can transmit it further, completing the human-mosquito life cycle.
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