Malaria

Gametocytes taken up with the blood meal fuse in the gut (stomach) of the female Anopheles mosquito.
The zygote formed is motile and is called the ookinete; it penetrates the stomach wall and forms an oocyst.
Sporozoites formed later migrate to the salivary glands.

When a female $Anopheles$ bites an infected person, the gametocytes enter the mosquito; fertilisation and development take place in its gut wall.
The sporozoites formed are released and migrate to the salivary glands of the mosquito, where they are stored.
When this infected mosquito bites another person, the sporozoites are injected along with the saliva. So sporozoites are found in the saliva of an infected female $Anopheles$.
A freshly moulted mosquito has not yet fed on an infected person, so it carries no sporozoites.
In humans the sporozoites go to the liver cells; the stages in RBCs are merozoites, trophozoites and gametocytes, and the spleen does not contain sporozoites.
Hence sporozoites are found in the saliva of the infected female $Anopheles$ mosquito.

$Plasmodium$ enters the body as sporozoites, which first multiply in the liver cells and then attack the red blood cells.
Inside the RBCs the parasite multiplies asexually; the RBCs then rupture, releasing the new parasites (merozoites) that enter fresh RBCs.
The rupture of RBCs is associated with the release of a toxic substance, haemozoin, which is responsible for the chill and high fever recurring every three to four days.
Sporozoites are not released from RBCs, and the destruction of gametocytes is not the cause of the fever.
Hence chill and fever occur when the parasite, after rapid multiplication inside RBCs, ruptures them and releases the stage that enters fresh RBCs.