Asexual Life Cycle of Plasmodium vivax

Sporozoite is the asexual stage of the Plasmodium. It is the infectious stage that infects humans. Sporozoites get transmitted from the female Anopheles to humans when the infected mosquito bites. The sporozoites reach the human liver cells and mature into schizonts.

1. Shri Shivaji Education Society, Amravati's Shri Pundlik Maharaj Mahavidyalaya, Nandura Rly. Dist. Buldana Topic: Asexual Life Cycle of Plasmodium vivax Class: B.Sc-I, Sem-I Shantaram Bhoye Assistant Professor M.Sc., NET-JRF, SET, M.A.(Eng.)

2. Life Cycle of Plasmodium vivax Life cycle of P. vivax is digenetic, that requires two hosts to complete its life cycle. One vertebrate host is man or any other vertebrate animal. Second invertebrate host is female Anopheles mosquito. It is reproduces both sexually as well as asexually. 1. Asexual cycle or schizogony: Occurs in the body of man where the parasite occurs inside liver cells and RBC. 2. Sexual cycle or sporogony: Occurs in the body of female Anopheles mosquito, where parasite occurs in the alimentary canal and salivary glands. Female Anopheles mosquito serve as the vector, which transfers the parasite from one man to another. Mr. Shantaram Bhoye, Assistant Professor, Shri Pundlik Maharaj Mahavidyalaya, Nandura Rly., Dist. Buldana

3. Asexual cycle of Plasmodium vivax in Man: It is occurs in the body of man. Parasites occurs inside liver cells and RBC. Reproduction occurs in asexual method known as schizogony. 1) Infection to the host or transmission of parasites: Infected female Anopheles mosquito bites a healthy person → to suck the blood → it injects some saliva into the blood stream of host (man) → Along with saliva thousands of sporozoites of Plasmodium are inoculated into the blood of host. Beginning of asexual life cycle. Mr. Shantaram Bhoye, Assistant Professor, Shri Pundlik Maharaj Mahavidyalaya, Nandura Rly., Dist. Buldana

4. 2) Sporozoites: It is infective stage of the parasites. It is minute, motile, slightly curved or sickle shaped organism, tapering at both ends. It contains vesicular nucleus and mitochondria. Anterior end cup like depression called apical cup. A pair of secretory organelles opens into the apical cup, which secretes proteolytic enzymes. This enzymatic secretion facilitate the penetration or entry of sporozoites into host cells. Mr. Shantaram Bhoye, Assistant Professor, Shri Pundlik Maharaj Mahavidyalaya, Nandura Rly., Dist. Buldana

5. Mr. Shantaram Bhoye, Assistant Professor, Shri Pundlik Maharaj Mahavidyalaya, Nandura Rly., Dist. Buldana

6. 3) Schizogony: In about half an hour after infection, sporozoites disappear from blood stream. Do not appear there again until 6 days. During this period they enter liver cells. Where reproduce by asexual method known as schizogony. Schizogony includes two phases: I) Liver schizogony II) Erythrocytic schizogony Mr. Shantaram Bhoye, Assistant Professor, Shri Pundlik Maharaj Mahavidyalaya, Nandura Rly., Dist. Buldana

7. I) Liver schizogony: Pre-erythrocytic phase: Inside liver cell, sporozoite becomes spherical and non-pigmented known as cryptozoite . Nucleus divides several times to form a multinucleate known as schizont. Schizont ruptures and liberate several thousand small, uninucleate cryptomerozoites in liver. Mature pre-erythrocytic schizont produces 12,000 cryptomerozoites . They pass into the blood circulation, attack on erythrocytes and begin erythrocytic cycle. Or they enter fresh liver cells to continue exo -erythrocytic cycle. This phase lasts for 8 days in P. vivax. Pre-patent period: The duration between the initial sporozoite infection or mosquito bite and the first appearance of the parasites in the blood is known as pre-patent period. (Range from 5 to 15 days.) Mr. Shantaram Bhoye, Assistant Professor, Shri Pundlik Maharaj Mahavidyalaya, Nandura Rly., Dist. Buldana

8. Mr. Shantaram Bhoye, Assistant Professor, Shri Pundlik Maharaj Mahavidyalaya, Nandura Rly., Dist. Buldana

9. B) Exo-erythrocytic phase: When cryptomerozoites of pre-erythrocytic phase enters into fresh liver cell then start exo -erythrocytic phase. In liver cell cryptomerozoite becomes spherical or round and non-pigmented known as metacryptozoite or phanerozoites . Its nucleus divides to form multinucleate schizont. When schizont ruptures, then produces several thousand meta- cryptomerozoites . Meta- cryptomerozoites are two types: i ) Micro- metacryptomerozoites : Cryptomerozoites are smaller, more numbers. They enter the RBCs to start erythrocytic cycle. ii) Macro- metacryptomerozoites : Cryptomerozoites are larger, less numbers. They remain in liver, attack on fresh liver cells and continue exo -erythrocytic cycle. This cycle repeated several times. Mr. Shantaram Bhoye, Assistant Professor, Shri Pundlik Maharaj Mahavidyalaya, Nandura Rly., Dist. Buldana

10. Mr. Shantaram Bhoye, Assistant Professor, Shri Pundlik Maharaj Mahavidyalaya, Nandura Rly., Dist. Buldana

11. Relapse: When the immunity or the resistance of the host falls down, the parasites from the reservoirs may re-infect the blood and cause malaria, which is known as relapse. II) Erythrocytic Schizogony: It is begins when the erythrocytes (RBCs) are attacked either by pre-erythrocytic cryptomerozoites or by exo -erythrocytic micro- metacryptomerozoites . A) Trophozoite: After entering into RBCs , micro- metacryptomerozoite becomes rounded, disc like in shape, known as trophozoite. It has single large nucleus. It grows by ingesting the haemoglobin of RBCs. Mr. Shantaram Bhoye, Assistant Professor, Shri Pundlik Maharaj Mahavidyalaya, Nandura Rly., Dist. Buldana

12. B) Signet ring stage: Trophozoite ingest large amount of cytoplasm of RBCS, due to vacuoles appears in parasite. Vacuole gradually increase in size and pushes the nucleus to one side in the peripheral cytoplasm. This refer to as signet ring stage. Number of pinocytic vesicles also appear at periphery of the parasites. Digestive enzymes are secreted into vacuole and vesicles. Ingested haemoglobin is decomposed into amino acids and haematin . This amino acid are used by parasites to synthesize its own proteins and heamatin forms yellowish brown or black toxic malarial pigments known as haemozoin. Haemozoin are responsible for malarial fever. Mr. Shantaram Bhoye, Assistant Professor, Shri Pundlik Maharaj Mahavidyalaya, Nandura Rly., Dist. Buldana

13. C) Amoeboid stage: In this stage, vacuole disappears and the parasite becomes amoeboid in shape. RBCs becomes large (double its original size) and slightly paler due to loss its haemoglobin. On surface of parasite develops numerous, fine and charactristics granules known as Schuffner granules. D) Schizont: After active feeding, amoeboid trophozoite becomes rounded known as shizont . It multiplies asexually by process known as erythrocytic schizogony or merogony. Its nucleus divides by multiple fission to form 6 to 24 daughter nuclei, which now called schizont. These nuclei come to on periphery region, while the haemozoin granules accumulate at the center. Thus, many small, oval, uninucleate parasites called erythrocytic merozoites or schizoites are formed. Mr. Shantaram Bhoye, Assistant Professor, Shri Pundlik Maharaj Mahavidyalaya, Nandura Rly., Dist. Buldana

14. E) Rosette Stage: Erythrocytic merozoites are arranged like petals of rose flower or cluster of grapes known as rosette stage. At the end, RBCs bursts/ ruptures and merozoites along with toxic haemozoin granules are set in blood plasma. One complete erythrocytic cycle takes 48 hours in P . vivax. Some merozoites attack on fresh RBCs and the erythrocytic cycle is repeated. Haemozoin granules released in blood cause malarial fever to the host. The patient becomes anaemic due to destruction of RBCs. Mr. Shantaram Bhoye, Assistant Professor, Shri Pundlik Maharaj Mahavidyalaya, Nandura Rly., Dist. Buldana

15. 4) Post-erythrocytic schizogony: Sometimes erythrocytic merozoites reach liver cells and divide by schizogony which is referred to as post-erythrocytic schizogony. 5) Incubation Period: The interval between mosquito bite or introduction of sporozoites into the human blood and appearance of malarial symptoms is known as incubation period. It ranges from 8-48 days, according to species. About 14 days in P. vivax . Mr. Shantaram Bhoye, Assistant Professor, Shri Pundlik Maharaj Mahavidyalaya, Nandura Rly., Dist. Buldana

16. 6) Formation of Gametocytes: Gametocytes are of two types: a) Male or Microgametocytes: These are smaller, less numerous. It has laterally placed, large nucleus and cytoplasm. b) Female or Macrogametocytes: These are larger, more numerous. It has small peripherally placed, compact nucleus and food laden cytoplasm. Mr. Shantaram Bhoye, Assistant Professor, Shri Pundlik Maharaj Mahavidyalaya, Nandura Rly., Dist. Buldana