How do sandflies cause Leishmaniasis?

Leishmaniasis is a disease caused by Leishmania donovani.
It has two hosts. Man is the primary host and sandfly is the secondary or intermediate host.
When a sandfly bites an infected man, it takes amastigote form of Leishmania from the blood of the man.
Then the parasites enter the midgut of the sandfly.
In the midgut, the parasites change into promastigote form.
Then they reproduce by means of longitudinal binary fission.
When the number of parasites is enormous, they come to the buccal cavity and pharynx of the sandfly.
When an infected sandfly bites a man, the parasites transferred into the man’s body from the buccal cavity of the sandfly.
This is the way how sandflies cause Leishmaniasis.