Sprozoites have a special predilection towards the salivary glands, so their concentration reaches a maximum in salivary ducts. When an infected female anopheles mosquito bites a susceptible person, a single bite is capable of transmitting infection.
Mature Quadrinucleate Cyst
Mature quadrinucleate cysts are the infective forms of Entamoeba histolytica. When these cysts are swallowed along with the contaminated food and drink by susceptible persons, they are capable of further development and can cause Amoebic dysentery, Amoebic liver abscess, etc.
Transmission of L. donovani from man to man is carried out by a certain species of sandfly of the genera Phlebotomus and Lutzomyia.
Sandfly introduce promastigote in the skin of the mammalian host which is later engulfed by reticuloendothelial cells, where it converts into intracellular amastigote form. Promastigotes are motile, elongated, extracellular stages of Leishmania donovani, having a single free flagellum. Leishmania donovani causes visceral leishmaniasis (kala-azar). Other species of Leishmania cause cutaneous and mucocutaneous leishmaniasis.
In Hookworm hatched L3 filariform larvae is the infective stage, transmission to humans is mainly via active skin penetration by the larvae or sometimes by oral route. Hyaluronidase activity of larvae facilities breakage of hyaluronic acid and passage through epidermis and dermis.
Other parasites and their infective stages are:
- Ascaris Lumbricoides (GI parasite): Mature fertilized egg (which contains Rhabiditiform larvae inside)
- Wuchereria bancrofti (Filariasis): Third larval Stage (L3)