Introduction
Genus Plasmodium
- Characteristics
- Habitat: Develops in blood-feeding female mosquitoes and vertebrate hosts.
- Infection Process: Injects parasites into vertebrates during a mosquito's blood meal.
- In Humans: Parasites multiply in the liver before entering the bloodstream to infect red blood cells, causing malaria.
- Transmission: Continues when mosquitoes ingest the parasite during a blood meal.
- Diversity: Over 200 known species, with 11 infecting humans and 5 causing human malaria.
- Key Species
- P. vivax: Most widespread, causes fever every 48 hours.
- P. falciparum: Causes the most severe symptoms, including irregular fever patterns.
- P. malariae: Characterized by a fever every 72 hours.
Life Cycle of Plasmodium
- Exoerythrocytic Cycle (Liver Phase):
- Female mosquitoes inject sporozoites that infect liver cells.
- Sporozoites multiply asexually in the liver.
- Erythrocytic Cycle (Blood Phase):
- Liver cells burst, releasing merozoites that infect red blood cells.
- Inside RBCs, merozoites become trophozoites, then mature into gametocytes and schizonts.
- Schizonts burst, releasing more merozoites that infect additional RBCs.
- Gametocytes are ingested by mosquitoes during another blood meal.
- Sporogonic Cycle (Mosquito Phase):
- Ingested gametocytes undergo sexual reproduction within the mosquito, forming oocysts.
- Oocysts release sporozoites that migrate to the mosquito's salivary glands, ready to infect a new host.
Symptoms and Morphological Differences
- P. vivax: Enlarged erythrocytes with cytoplasmic dots, more than 12 merozoites per schizont.
- P. falciparum: Multiple ring forms in host cells, double chromatin dots, prone to sticking to blood vessel walls; severe cases lead to cerebral malaria.
- P. malariae: No spots in erythrocytes' cytoplasm, up to 12 merozoites per schizont.
Malaria Overview
- Prevalence: Common in tropical and subtropical regions due to ideal mosquito breeding conditions (rain, warmth, stagnant waters).
- Impact: In 2010, approximately 219 million cases of malaria were reported, with deaths ranging between 660,000 and 1.2 million annually.
- Diagnostics: Blood smears or rapid diagnostic tests based on antigen detection.
- Clinical Manifestations: Fever and headache, which may progress to severe complications like coma or death.
Erythrocytic Phase Details
- Initiation: Begins with hepatic merozoites attaching to specific receptors on RBCs, followed by invasion and formation of a parasitophorous vacuole.
- Development: The parasite progresses from a ring-shaped trophozoite to an ameboid or band-shaped form.
- Reproduction: Nuclear division in the schizont leads to formation of 6-24 merozoites.
- Cycle Progression: Rupture of infected erythrocytes releases merozoites, causing clinical symptoms; some merozoites become gametocytes, continuing the cycle without causing RBC lysis.