PLASMODIUM VIVAX |HINDI EXPLAINATION скачать в хорошем качестве

PLASMODIUM VIVAX |HINDI EXPLAINATION

Plasmodium vivax is a protozoal parasite and a human pathogen. This parasite is the most frequent and widely distributed cause of recurring malaria.[2] Although it is less virulent than Plasmodium falciparum, the deadliest of the five human malaria parasites, P. vivax malaria infections can lead to severe disease and death, often due to splenomegaly (a pathologically enlarged spleen).[3][4] P. vivax is carried by the female Anopheles mosquito; . vivax has a complex life cycle. It infects a definitive insect host, where sexual reproduction occurs, and an intermediate vertebrate host, where asexual amplification occurs. In P. vivax, the definitive hosts are Anopheles mosquitoes (also known as the vector), while humans are the intermediate asexual hosts. During its life cycle, P. vivax assumes many different physical forms.[citation needed] Asexual forms: Sporozoite: Transfers infection from mosquito to human Immature trophozoites (Ring or signet-ring shaped), about 1/3 of the diameter of a RBC. Mature trophozoites: Very irregular and delicate (described as amoeboid); many pseudopodial processes seen. Presence of fine grains of brown pigment (malarial pigment) or hematin probably derived from the haemoglobin of the infected red blood cell. Schizonts (also called meronts): As large as a normal red cell; thus the parasitized corpuscle becomes distended and larger than normal. There are about sixteen merozoites. Sexual forms: Gametocytes: Round. P. vivax gametocytes are commonly found in human peripheral blood at about the end of the first week of parasitemia. Gametes: Formed from gametocytes in mosquitoes. Zygote: Formed from combination of gametes Oocyst: Contains zygote, develops into sporozoites Human infectionEdit P. vivax human infection occurs when an infected mosquito feeds on a human. During feeding, the mosquito injects saliva to prevent blood clotting (along with sporozoites), thousands of sporozoites are inoculated into human blood; within a half-hour the sporozoites reach the liver. There they enter hepatic cells, transform into the trophozoite form and feed on hepatic cells, and reproduce asexually. This process gives rise to thousands of merozoites (plasmodium daughter cells) in the circulatory system and the liver.[citation needed] The incubation period of human infection usually ranges from ten to seventeen days and sometimes up to a year. Persistent liver stages allow relapse up to five years after elimination of red blood cell stages and clinical cure. Liver stageEdit The P. vivax sporozoite enters a hepatocyte and begins its exoerythrocytic schizogony stage. This is characterized by multiple rounds of nuclear division without cellular segmentation. After a certain number of nuclear divisions, the parasite cell will segment and merozoites are formed. There are situations where some of the sporozoites do not immediately start to grow and divide after entering the hepatocyte, but remain in a dormant, hypnozoite stage for weeks or months. The duration of latency is thought to be variable from one hypnozoite to another and the factors that will eventually trigger growth are not known; this might explain how a single infection can be responsible for a series of waves of parasitaemia or "relapses".[35] It has been assumed that different strains of P. vivax have their own characteristic relapse pattern and timing. However, such recurrent parasitaemia is probably being over-attributed to hypnozoite activation.[36] Two newly recognized, non-hypnozoite, probable contributing sources to recurrent peripheral P. vivax parasitaemia are erythrocytic forms in bone marrow and the spleen.[37]