Q.Describe the life cycle of Plasmodium vivax in mosquito.

Inside the female Anopheles mosquito, Plasmodium vivax undergoes its sexual (sporogonic) cycle: gametocyte fusion to zygote to ookinete to oocyst (sporogony) to sporozoites in the salivary glands, ready to infect a new human.

When a female Anopheles mosquito bites an infected human and takes up blood containing mature gametocytes (the sexual stages of Plasmodium vivax) along with other blood stages, the following events occur inside the mosquito's gut - this is the sexual (sporogonic) cycle, and the mosquito is the definitive host:

1. Gamete formation: In the mosquito's stomach, the ingested gametocytes are activated.

   • The microgametocyte (male) undergoes exflagellation, throwing out several thin, thread-like, motile microgametes.
   • The macrogametocyte (female) matures directly into a single macrogamete.

2. Fertilization: A microgamete fuses with a macrogamete to form a diploid zygote.

3. Ookinete formation: The zygote elongates and becomes actively motile, forming a worm-like structure called the ookinete, which penetrates through the epithelial lining of the mosquito's midgut (stomach wall) and comes to lie beneath the outer epithelium (between the epithelium and the basement membrane).

4. Oocyst and sporogony: Here, the ookinete rounds up and secretes a cyst wall, becoming an oocyst. Inside the oocyst, the nucleus undergoes repeated (meiotic followed by mitotic) divisions - a process called sporogony - producing thousands of thread-like infective stages called sporozoites.

5. Release and migration to salivary glands: The mature oocyst ruptures, releasing the sporozoites into the mosquito's haemocoel (body cavity). These sporozoites migrate through the haemolymph and specifically invade and accumulate in the mosquito's salivary glands.

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