Morphology of plasmodium
Blood stages of plasmodium are as follows;
1. young trophozoites (ring forms)
2. growing trophozoites
3. mature trophozoites
4. mature schizonts
5. macrogamerocytes
6. microgametocytes.
The merozoite is the youngest form of the parasite, appearing as the result of the splitting of a mature schizont. It is spherical or oval and small in size (1-2 micrometer). The merozoites is the youngest form of the parasite, appearing as the result of the splitting of a mature schizont. It is spherical or oval and small in size (1-2 micrometer). The merozites consists of cytoplasm and a nucleus. Merozites penetrate into the erythrocytes and give rise to asexual forms of the parasites. The young trophozoite (ring-form stage) grows larger and a vacoule appears in its cytoplasm. At this stage the malaria parasite has irregular contours movement. As it grows, a pigment appears within it (a product of hemoglobin breakdown) in the form of dark-brown spots. The mature schizont becomes rounded and pulls in its pseudopodia by the time of complete merulation, occupying almost the entire erythrocytes. The nucleus and cytoplasm divide and form from 6 to 24 merozoites (it depends on the species of the parasite). The pigment accumulates in the center in a compact clump. The erythrocytes are destroyed by merozoites. The merozoites release into the blood plasma. Some of them again penetrate into erythrocytes. The gametocytes are sex cells and are subdivided into female (macrogametocytes) and male (microgametocytes) cells. The macrogametocytes are 12-14 micrometer, their nuclei are small. The microgametocytes are smaller, their nuclei are large.
Life cycle
The life cycle involves sexual stage (sporogony) in the mosquito (Anopheles) and asexual stage (schizogony) in humans, Man is an intermediate host and mosquito is a definitive host. The life cycle passes 3 stages: two in man: "Exoerythrocytic schizogony" (liver phases) and "Erythrocytic schizogony" (blood phases); one in mosquito: "Sporogony"
Exoerythrocytic schizogony (liver phase)
1. Mosquito bites man, takes blood meal and injects sporozoites from its salivary gland into the blood.
2. Sporozoites travel through blood to the liver, multiply asexually to form merozoites, which upon liver cell rupture, Merozoites are released into the bloodstream and infect erythrocytes.
Erythrocytic schizogony (blood phase)
1. Merozoites enter the erythrocytes, forming a ring-like trophozoite. Mature trophozoites asexually divide to form schizonts.
2. Schizont develops into merozoites, then lyse the erythrocytes membrane, leading to periodic paroxysms of disease due to resultant parasitemia. P.Ovale P.Vivax, P. Falciparum- membrane lysis in 48 hours, P.malariae- membrane lysis in 72 hours.
3. Some merozoites are developed into macrogametocytes and microgametocytes.
Sporogony
1. Mosquito ingests gametocytes with blood meal
2. Gametocytes enter mosquito gut.
3. Zygote, formed from fertilization, invades gut wall to form an oocyst within 24 hours following ingestion.
4. Sporozoites are formed, released into the stomach, migrate to salivary glands, then injected into human with blood meal.
Clinical Manifestations
The incubatory period in tertian malaria lasts from 10 days to 11 months in quartan malaria, from 21 to 42 days, and in tropical malaria, from 9 to 16 days. A malarial attack is produced by result of the body reaction to protein substances appearing in the blood due to erythrocyte dissociation. The most characteristic symptom of malaria is fever. Other common symptoms included anemia, splenomegaly, hepatomegaly.
Laboratory diagnosis comprises microscopy of thin and thick films blood smears stained and recognition of the different stages of the parasite (trophozoites, schizonts, gametocytes).
Malaria may be prevented by chemo-prophylaxis and personal protective measures against the mosquito vector (Anopheles). see also malaria-disease-understanding-basic facts about malaria
source
0 comments: