Plasmodium (the malarial parasite) is a sporozoan protist which completes its life cycle in two hosts :
(i) Female Anopheles (primary host) and
(ii) Human beings (secondary host).
As the female Anopheles mosquito feeds on blood only it can serve as vector host. Its infective stage is sporozoite, which is spindle shaped or sickle shaped and uninucleate organism capable of wrigling movement. This was first discovered by C Laveran in 1880.