When an Anopheles mosquito bites a person with malaria, gametocytes are released into the mosquito’s saliva. The sexual cycle of the malaria parasite in the mosquito is completed in two stages. Gametogony and sporogony.
1. Gametogony
The process of gamete formation is called gametogony. The stages of gametogeny are:
(i) Formation of Pungametes: The process of formation of pungametes or spermatozoa is called spermatogenesis. In the process of exflagellation, the nucleus of each microgametocyte divides to produce 4-8 nuclei. At this time 4-8 projections are formed in the cytoplasm. This is called cytoplasmic projection. One nucleus enters each projection. Each projection with a nucleus develops into a pungamete or microgamete. Pungamites swim for fertilization.
(ii) Formation of strygametes: The process of formation of strygametes or ovules is called oogenesis. Each macrogametocyte gives rise to one strigamete or macrogamete. One end of the macrogamete swells to form the fertilization cone. The cone region is called the Fertilization Cone or Reception Cone. The nucleus of the egg is located near the cone.
(iii) Fertilization: The gametes move individually towards the fertilization cone of the ovule. One sperm enters each egg. Later their nuclei fuse to form a zygote. This process is called fertilization. Fertilization is completed within 20-22 hours.
(iv) Wookinet/Vermicule: After 12-14 hours the quiescent spherical zygote becomes elongated and motile. It is called wokkinet or vermicule. Uokinetes are 18-24 microns in length and 3-5 microns in width.
(v) Oocysts: Within 24 hours the ookinetes break through the wall of the mosquito crop and come out and take spherical shape. Then within 40 hours it is covered with a thin film. It is called a oocyst. The nucleus of the oocyst divides first by meiosis and then by mitosis. Meiosis of oocyst is called postzygotic meiosis. A mosquito crop may contain 50-500 oocysts. The resulting oocysts appear spongy and 4-5 times larger in size (50-60 µ).
2. Sporogony
The process of sporozoite formation is called sporogony. The oocyst grows by consuming food. Its nucleus divides repeatedly by first mitosis and then meiosis to form many haploid nuclei. Cytoplasm accumulates around each nucleus to form spherical cells. Later round cells transform into sickle or macule shaped sporozoites. About 10,000 sporozoites are produced from each oocyst. The sporozoites reside in the hemocele of the mosquito. At this time, if the mosquito bites a healthy person, the sporozoite enters the person’s body. About 10% of sporozoites enter the human body during a single bite. A mosquito’s salivary gland can contain up to 326,000 sporozoites. The sporozoites remain in the salivary glands of the mosquito for about 60 days. It takes about 10-20 days from stinging to sporozoite formation.