Source: re-drawn from CDC public health image library

The diagram above shows the sporogonic cycle. This is the part of the lifecycle of the parasite which occurs in the vector (mosquito).

As in the host (human) the parasite develops and multiplies inside the mosquito. However, whilst this reproduction was asexual in the human, in the mosquito it is sexual.

The stages of the cycle are (the letters correspond to the diagram above):

A. As the mosquito feeds on the infected human, the gametocytes which developed in the human in stage 4 are ingested by the mosquito - they enter the mosquito's stomach.

B. The male gametocytes are called microgametocytes.

C. The female gametocytes are called macrogametocytes.

D. When the micro- and macro-gametocytes come together, fertilization occurs and a zygote is formed.

E. This zygote elongates and becomes a ookinate which can penetrate (go through) the mosquito's midgut wall, leaving the stomach.

F. These ookinates develop into oocysts which contain lots of sporozoites.

G. After a while the oocysts rupture, releasing the sporozoites.

H. The released sporozoites move to the salivary glands of the mosquito.

I. Next time the mosquito takes a blood meal these sporozoites are injected into the human and the cycle begins again at stage 1.