14-07-2012, 12:37 PM
MALARIAL PARASITE
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GAMETOCYTE-
The gametocyte is the form that infects the mosquito and reproduces itself, as if it were both sexes. When the mosquito has sucked blood containing gametocytes, these pass into the salivary glands of the mosquito, where they develop into a new form, the sporozoite. The infection can then move on.
• SPOROZOITE-
The sporozoite can be passed on to man when the mosquito bites, injecting its saliva into the tiny blood vessels. The sporozoite travels with the blood to the liver and enters the liver cells. In the liver some of the sporozoites divide (tachysporozoites) and become thousands of merozoites.
• MEROZOITES-
The merozoites are released from the liver to the blood where they are taken up by the red blood corpuscles. Some of these turn into ring-formed trophozoites, which split again to form schizonts.
• SCHIZONTS-
Schizonts burst the red blood corpuscles at a certain moment, releasing the merozoites. This release coincides with the violent rises in temperature during the attacks seen in malaria.
The trophozoites that are left over during division can, in the course of the next day, develop into the sexual form, the gametocyte, which can be taken up by a blood-sucking mosquito and start another cycle.The incubation period (time from infection to development of the disease) is usually about 10 to 15 days. This period can be much longer depending on whether any antimalarial medication has been taken.
Plasmodium ovale and Plasmodium vivax can produce a dormant form, a hypnozoite, which can cause relapses of the disease months and even years after the original disease (relapsing malaria), because it is dormant in the liver cells. This is why it is very important after these infections to be treated with primaquine to kill the liver stages. (Primaquine cannot be used by people with a condition called G6PD-deficiency.)
1) THE LIFE CYCLE OF PLASMODIUM FALCIPARUM MALARIA PARASITE.
Malaria is caused by infection with an obligate, intracellular protozoan parasite of the genus Plasmodium. Of the four species that infect humans (Plasmodium falciparum,Plasmodium vivax, Plasmodium ovale and Plasmodium malariae), it is P. falciparum that is responsible for virtually all deaths. The life cycle of Plasmodium spp. is complex and somewhat specific to the parasite species.
(a) P. falciparum infection in humans begins when an infected Anopheles sp. mosquito takes a blood meal and injects infective sporozoites into the peripheral circulation.
(b) Within minutes, these sporozoites invade hepatocytes in the liver and, over approximately one week, undergo asexual multiplication, producing tens of thousands of merozoite forms of the parasite.
© When the infected hepatocyte ruptures, merozoites are released into the peripheral circulation.
(d) The merozoites invade red blood cells .
(e)complete another round of multiplication within 48–72 h, with the production of 16–20 additional merozoites per rbc’s, which devour the rbc’s haemoglobin in the process.
(f)Thereleasedmerozoites invade additional rbc’s and carry on the cycle. It is the synchronous release of merozoites that is thought to be responsible for the periodic fevers associated with malaria.
(g) Some invading merozoites do not divide, but differentiate into male (microgametocyte) and female (macrogametocyte) sexual forms.