Malaria Transmission Cycle: Mosquito Vector to Human Host and Back

Step-by-Step Plasmodium Transmission

1. Infected Mosquito Bite: Sporozoites injected into human bloodstream.
2. Liver Stage: Sporozoites invade hepatocytes → mature into schizonts → release thousands of merozoites.
3. Blood Stage: Merozoites invade RBCs → asexual replication (ring → trophozoite → schizont) → rupture → more merozoites → cyclic fevers.
4. Gametocyte Formation: Some merozoites differentiate into sexual forms (male/female gametocytes) in RBCs.
5. Mosquito Ingestion: Mosquito takes blood meal containing gametocytes.
6. Mosquito Gut: Gametocytes fuse → zygote → motile ookinete → penetrates midgut wall → oocyst.
7. Sporozoite Maturation: Oocyst ruptures → sporozoites migrate to salivary glands.
8. New Human Infection: Mosquito bites another human → sporozoites injected → cycle repeats.

Key Points

• One infected mosquito can infect multiple people.
• Transmission intensity depends on vector density, longevity, human biting rate, and parasite prevalence.
• Control targets: vector (ITNs, IRS), parasite (treatment), and human-vector contact.