INTRODUCTION• Malaria is a mosquito-borne infectious disease caused by intracellular protozoan parasite Plasmodium.• Characterized by cycles of shaking, chills, fever, sweating and anaemia.• Affects 500 million and kills more than 1 million people each year.• Endemic in tropical and subtropical regions – Sub-Saharan Africa, Asia and Latin America.• In India, about 1.5 – 2 million cases and 1000 malarial deaths are reported annually (mostly from tribal, hilly and inaccessible areas).
Causative AgentsPlasmodium species Human infectionPlasmodium vivax Benign tertian malariaPlasmodium falciparum Malignant tertian / Pernicious malaria (most common and fatal) (complications – Cerebral malaria and Black water fever)Plasmodium malariae Quartan malariaPlasmodium ovale Ovale tertian malaria
Contd..• All forms are transmitted by the infective bite of female Anopheles mosquitoes.• Transmission through blood transfusion can also occur.• Man develops disease after 10 to 14 days of being bitten by an infective mosquito.
Ring-forms and gametocytes of Plasmodium falciparum in human blood.
Lifecycle of Plasmodium• 2 stages 1) Sexual phase in the mosquito 2) Asexual phase in humans a) Exoerthrocytic (Pre-erythrocytic) shizogony b) Erythrocytic shizogony• The infectious stage of malaria - Sporozoite (found in the salivary glands of female mosquitoes).
Life cycle in humans• Mosquito takes a blood meal → Sporozoites released into human’s blood → infect liver cells• EXO-ERYTHROCYTIC STAGE :- Parasites inside heparocyte → Shizont (containing thousands of merozoites) → infected hepatocytes release about 30,000 Merozoites (asexual, haploid forms) → quickly infect red cells. * [P. vivax and P. ovale form latent Hypnozoites in hepatocytes, which cause relapses of malaria long after initial infection]
ERYTHROCYTIC STAGE :-• Within the red cells the parasites grow in a membrane-bound digestive vacuole, hydrolyzing haemoglobin through secreted enzymes.• A) Continuation of asexual reproduction - Most of the parasites develop into Trophozoites → Schizont → multiple chromatin in schizonts develop into Merozoites → Red cell lysis & merozoites infect other red cells. B) Production of gametocytes - Some parasites develop into sexual forms called Gametocytes → infect the mosquito.