Malaria Parasite Overview PDF

Phylum Apicomplexa Overview: Class Sporozoea ○ Subclass Coccidiasina Order Eucoccidia Suborder Haemosporina: Genus Plasmodium (e.g., species causing malaria) Suborder Eimeriina: Genera Toxoplasma, Cr...

Phylum Apicomplexa Overview: Class Sporozoea ○ Subclass Coccidiasina Order Eucoccidia Suborder Haemosporina: Genus Plasmodium (e.g., species causing malaria) Suborder Eimeriina: Genera Toxoplasma, Cryptosporidium, Isospora (causing toxoplasmosis, cryptosporidiosis, and isosporiasis) Subclass Piroplasmasina Genus Babesia (causes babesiosis, similar to malaria) General Characteristics of Apicomplexa: Morphology: ○ Subpellicular microtubules ○ Apical complex: Contains distinctive organelles: Rhoptries Micronemes Dense granules ○ These structures aid in host cell invasion. Genus Plasmodium: Infects red blood cells in humans. Four Species Infecting Humans: ○ Plasmodium falciparum: Infects all red blood cells (RBCs) – malignant tertian malaria ○ Plasmodium vivax: Infects reticulocytes (young RBCs) – benign tertian malaria ○ Plasmodium ovale: Infects reticulocytes – benign tertian malaria ○ Plasmodium malariae: Infects older RBCs – quartan malaria ○ Plasmodium knowlesi: Has a 24-hour blood stage cycle, historically rare in humans Plasmodium falciparum: Epidemiology: ○ Vector: Female Anopheles mosquitoes (Anopheles gambiae complex, A. funestus, and others)  ○ Distribution: Mostly in tropical regions ○ Children and newly exposed individuals are at higher risk. ○ WHO (2023): 247 million malaria cases, 619,000 deaths globally, primarily due to P. falciparum. ○ Mortality Rate: 14.3 deaths per 100,000 population at risk. Plasmodium Life Cycle: ○ Sporozoite: Infective form transmitted by mosquito bite. ○ Merozoite: Free parasites released from infected cells (RBCs). ○ Ring stage: Early trophozoite. ○ Trophozoite: Feeding stage within RBCs. ○ Schizont: Undergoes asexual reproduction, leading to release of merozoites. ○ Gametocytes: Sexual forms that can be taken up by a mosquito to continue the cycle. Clinical Presentation: ○ Pre-patent Period: 10-14 days after the bite. ○ Fever Cycles: Occur every 36 to 72 hours, with characteristic symptoms: Chills, hot stage (high fever, altered consciousness, abdominal pain, diarrhea), sweat stage (fatigue). ○ Complications: Cerebral malaria, renal failure, gastroenteritis, severe anemia, hypoglycemia. Why is P. falciparum more severe?: ○ Infects all types of blood cells. ○ Trophozoite and schizont stages are sequestered in capillaries, evading immune detection. ○ Infected cells express ‘knobs’ (mediated by PfEMP), which adhere to endothelial cells in the brain, kidneys, etc. ○ Antigenic variation allows parasites to evade immune responses. Natural Resistance: ○ Sickle Cell Trait (HbAS): Provides some protection against severe malaria. ○ G6PD Deficiency: Common in Southeast Asia; reduces parasite growth in RBCs. ○ Thalassemias: Reduced production of hemoglobin also offers resistance. Other Plasmodium Species: 1. Plasmodium vivax & Plasmodium ovale: ○ Epidemiology: Wider distribution than P. falciparum (e.g., temperate climates such as Siberia). Resistance in West Africa due to the absence of Duffy antigen, required for invasion by P. vivax. ○ Pathogenesis:  Benign tertian malaria: Fevers every 48 hours. Infect reticulocytes (limiting parasitemia to ~1%). Hypnozoites (dormant forms) persist in the liver and can cause relapses. 2. Plasmodium malariae: ○ Pathogenesis: Causes quartan malaria (fevers every 72 hours). Infects older RBCs; less pathogenic and rarely acute. Can remain dormant in the liver for months or years, causing long-term recrudescence. Diagnosis: Blood Smear: Giemsa-stained samples. ○ Thin smear: Detailed observation of morphology. ○ Thick smear: Detection of low levels of parasitemia. Molecular Techniques (PCR): For specific identification of species. Parasite Stages and Intervention Points: Targets for Drug and Immune Therapy: ○ Vector control: Insecticides, larvicides (e.g., DDT). ○ Liver stage drugs: Primaquine. ○ Blood stage drugs: Chloroquine (with increasing resistance), Artemisinin, Doxycycline, Mefloquine. Anopheles Mosquito (Malaria Vector): Various Anopheles species spread malaria, each with different geographical distributions: ○ An. gambiae (Africa), An. albimanus (Central America), An. darlingi (South America), An. stephensi (India), etc. Life Cycle: ○ Females lay eggs on water. ○ Larvae hatch and develop into pupae, which then become adult mosquitoes. ○ Adult female mosquitoes need blood meals to produce eggs.