Life Cycle of Plasmodium.

Malarial parasite ie Plasmodium have a very complex and multistage life cycle in human and female Anopheles mosquito.

1. Department of Microbiology (Ch. Charan Singh University Campus, Meerut) Topic: Life-Cycle of Plasmodium Presented By: Manisha Sirohi M.Sc.(Microbiology) 1 st Semester.

2. CONTENTS Introduction Life-Cycle of Plasmodium Human Cycle Pre- erythrocytic schizogony Erythrocytic schizogony Gametogony Exoerythrocytic schizogony Mosquito Cycle Overview of Life-Cycle of Plasmodium References

3. INTRODUCTION Plasmodium is a common spore-forming sporozoan parasite on human which causes malaria. Malarial parasites infecting humans belong to four species of Genus Plasmodium: Plasmodium vivax, Plasmodium falciparum, Plasmodium malariae and Plasmodium ovale . These malarial parasites are worldwide in distribution. In India, P.vivax and P.falciparum are very common. P.falciparum is the most dangerous species followed by P.vivax . As per recent estimates about 300 million people suffer from malaria and about 2-4 million die each year.

4. Life-Cycle of Plasmodium. The malarial parasites pass their life cycle in two hosts i.e. man (intermediate host) and female A nopheles mosquito (definitive host).

5. Human Cycle The sporozoite is the infective form of the malarial parasite. These sporozoites are present in the salivary gland of female Anopheles mosquitoes. Man gets infection by the bite of infected mosquito and sporozoites are introduced directly into the blood circulation. Thus, human cycle starts and it comprises of following stages: ( i ) Pre- erythrocytic schizogony (ii) Erythrocytic schizogony (iii) Gametogony (iv) Exo- erythrocytic schizogony

6. Life cycle of P lasmodium Image:GRB Objective Zoology( Dr.R.K . Pillai)

7. ( i ) Pre- erythrocytic schizogony : Sporozoites undergo a developmental phase inside the liver cells known as pre- erythrocytic schizogony . The sporozoites (elongated and spindle-shaped) become rounded inside the liver parenchymal cells. They undergo multiple nuclear division and develop into schizont . The size of schizont varies in different species and it contains 20,000-50,000 merozoites . The pre- erythrocytic cycle lasts for 8 days in P.vivax , 6 days in P.falciparum , 13-16 days in P.malariae and 9 days in P.ovale . After completion of this cycle, the liver cells rupture and release merozoites into the blood stream.

8. (ii) Erythrocytic schizogony : The merozoites released from pre- erythrocytic schizogony penetrate red blood cells. They pass through the stages of trophozoite , schizont and merozoite (See Fig.). The red blood cells rupture to release the merozoites which attack new red blood cells and continue their erythrocytic schizogony repeating the cycle. Erythrocytic stages of different species of Plasmodium (Image). Image:Medical Parasitology(CP Baveja,V Baveja )

9. (iii) Gametogony : Some merozoites of erythrocytic schizogony develop into male and female gametocytes known as microgametocytes and macrogametocytes respectively. They develop in the red blood cells. The microgametocytes of all the four species are smaller in size, cytoplasm stains light blue and the nucleus is large and diffuse. In contrast, the macrogametocytes are larger, the cytoplasm stains deep blue and the nucleus is small and compact. Gametocytes of Plasmodium species(Image). Image:Medical Parasitology(CP Baveja,V Baveja )

10. (iv) Exoerythrocytic schizogony : The exoerythrocytic schizogony cycle resembles the pre- erythrocytic cycle. Some sporozoites , on entering into liver cells, do not undergo asexual multiplication but enter into a resting (dormant) phase known as hypnozoite . After some period (usually up to 2 years), hypnozoites reactivate to become schizonts and release merozoites . These merozoites attack red blood cells and are responsible for relapse of malaria. Exoerythrocytic schizogony is absent in P.falciparum , therefore, relapses do not occur in malaria caused by P.falciparum .

11. Mosquito Cycle Gametocytes formed in human host are then transferred to mosquito for further development. Female Anopheles ingest both the asexual and sexual forms of the parasite from the blood meal of human. Only the mature sexual forms are capable of further development in the mosquito and rest die immediately. In the midgut of the mosquito, one microgametocyte develops into 4 to 8 thread like filamentous structures named microgametes. From one macrogametocyte only one macrogamete is formed.

12. Microgamete penetrates into a macrogamete. (Fertilization) Formation of zygote. (Fertilized macrogamete) Formation of ookinete . (Zygote lengthens and matures) Formation of oocyst. ( Ookinete develops) Development of sporozoites . (Inside oocyst)

13. After the formation of sporozoites the oocyst ruptures and releases sporozoites in the body cavity of the mosquito. Sporozoites are then distributed into various organs and tissues of the mosquito. They have a special predilection for salivary glands. The mosquito is now capable of transmitting the infection to man.

14. Overview of Life Cycle of Plasmodium Image:Medical Parasitology(CP Baveja,V Baveja )

15. REFERENCES Baveja C.P. and Baveja V. Medical Parasitology. Arya Publishing Company. Baveja C.P. Textbook of Microbiology. Arya Publications. Dubey R.C. and Maheshwari D.K. A Textbook of Microbiology. S.Chand . Pillai R.K. GRB Objective Zoology. Prakash Publications