It consists of 2 phases –
- Asexual cycle – In human
- Sexual cycle – In mosquito
ASEXUAL CYCLE
It begins when an infected mosquito bites a person and infests the sporozoite. The cycle consists of 4 phases, a brief description is as follows :
- Hepatic Phase : The sporozoite disappears within 60 min from the peripheral circulation. After 1-2 weeks of development, they become hepatic schizont and eventually burst releasing a shower of merozoites.
- Erythrocytic Phase : Many of the merozoites are quickly destroyed but a significant number attach to specific receptor sites in the RBC and pass through the stage of trophozoite. The erythrocytic phase ends with the liberation of merozoite which infect fresh red blood cell.
- Gametogony : In all species of malaria some erythrocytic forms do not divide but become male and female gametocyte. These are the sexual forms which are infective to man.
SEXUAL CYCLE
The sexual cycle begins when gametocyte are ingested by vector mosquito when feeding an infective person. The first event that takes place is exflagelation of male gametocyte called ‘microgamete’ and of female gametocyte called ‘macrogamete’.
By chemotoxins, microgamete’s attracted towards macrogamete and causes fertilization of female gamete and the zygote is formed which is at first motionless but within 18-24 hrs it becomes motile. This is called ookinete. Ookinete penetrates stomach wall of mosquito and develop into an oocyte which grows rapidly and develops with its numerous sporozoite.
When mature, the oocyte burst and liberate sporozoite into the body cavity. Many of this migrate to salivary gland of mosquito and then becomes infective to man.
