Infective Stages of the Parasites (with examples and descriptions)

Sporozoite of Malarial Parasite

Plasmodium Vivax (Malaria): Sporozoite
Sprozoites has special predilection towards the salivary glands, so their concentration reach maximum in salivary ducts. When an infected female anopheles mosquito bites a susceptible person,  a single bite is capable of transmitting infection.

 

Entamoeba histolytica (Causes-Amoebic dysentery): Mature Quadrinucleate Cyst

Mature Quadrinucleate Cyst of Entamoeba histolytica

Mature quadrinucleate cysts are the infective forms of Entamoeba histolytica. When these cysts are swallowed along with the contaminated food and drink by susceptible person, they are capable of further development and can cause Amoebic dysentery, Amoebic liver abscess etc.

Leishmania donovani (Visceral Leishmaniasis or Kala-azar): Promastigote

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 reticulo-endothelial cells, where it converts into intracellular amatigote 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.

Promastigote form of Leishmania

Hookworm (GI Parasite): Filariform larvae

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: 

  1. Ascaris Lumbricoides (GI parasite): Mature fertilized egg (which contains Rhabiditiform larvae inside)
  2. Wuchereria bancrofti (Filariasis): Third larval Stage (L3)