Malaria Overview and Life Cycle

Malaria Overview

• Malaria is a disease caused by Plasmodium species (blood protozoa)
• Different Plasmodium species cause distinct types of malaria, each with varying prevalence
  • Plasmodium vivax: Benign tertian malaria, widespread
  • Plasmodium ovale: Ovale tertian malaria, mostly in West Africa
  • Plasmodium malariae: Quartan malaria, uncommon except in Africa
  • Plasmodium falciparum: Malignant tertian malaria, most common in Africa

Global Distribution

• A map shows global distribution of malaria prevalence in 2015, categorized by regions with no transmission, controlled malaria, and eliminated malaria.

Life Cycle

• Anopheles mosquito bites infected person. Mosquito ingests infected red blood cells (RBCs).
• A Plasmodium life cycle passes through liver and blood stages via sporozoites.
• Symptoms appear during the blood phase when RBCs rupture every 3, 4 days depending on species, releasing parasite metabolites and triggering an immune response.

Pathogenesis

• Malaria starts with an incubation period, often followed by influenza-like symptoms.
• Malaria paroxysms (attacks) occur, characterized by recurring cycles of symptoms.
• Paroxysm symptoms include: chills, fever, and sweats. Cycles correlate with parasite erythrocytic replication/rupture.
• Rupture of infected red blood cells, release of parasite metabolites, and host immune response.

Clinical Picture

• The disease progresses through three stages: cold, hot, and sweating.
  • Cold stage features sudden chills, extreme cold, and rising temperature.
  • Hot stage presents with headache, high fever, hot dry, and flushed skin.
  • Sweating stage includes profuse sweating and cooling temperature.
• Clinical attacks decrease and eventually disappear.
• Recurrence (Relapse/Recrudescence) possible due to dormant hypnozoites/low-grade parasitaemia in different species, particularly P. vivax and P. ovale.

Hemolytic Anemia

• The severity of anemia depends on the Plasmodium species causing the infection
• P. vivax and P. ovale prefer young RBCs, resulting in less severe anemia
• P. malariae prefers old RBCs, leading to less severe anemia
• P. falciparum invades any age of RBCs, causing severe anemia.

Hepatosplenomegaly

• Enlarged liver and spleen (hepatosplenomegaly) due to enhanced phagocytosis of remnants of ruptured red blood cells and presence of Plasmodium, metabolites, and malaria pigment (Haemozoin).

Complications

• P. vivax, P. ovale, and P. malariae generally cause less severe disease.
• Chronic P. malariae infections can be complicated by nephrotic syndrome.
  • Excess antigen and antibody production form immune complexes that deposit in glomerular walls, activating the complement system leading to kidney damage, proteinuria.
• P. falciparum infection can cause a more severe disease.
  • Knob formation on infected RBCs cause these cells to stick to blood vessels of internal organs, reducing blood flow and organ damage. This can involve brain (cerebral malaria), intestines (diarrhoea, dysentery), lungs (lung oedema), liver (impaired glycogenolysis), kidneys (acute renal failure), and circulation (hypotension, shock).
• Hyper-reactive malarial splenomegaly (Tropical splenomegaly syndrome) may occur from repeated malaria attacks, marked spleen enlargement and increased IgM production.
• Blackwater fever is a severe complication of P. falciparum, involving massive intravascular haemolysis, jaundice, and hemoglobinuria.

Laboratory Diagnosis

• Thin and thick blood smears to identify the parasite stages and diagnose species.
• Rapid dipstick tests to detect circulating parasite antigen.
• Polymerase chain reaction (PCR) tests to detect parasite DNA/RNA in patient blood.

Malaria Pigments

• Malaria pigments (Haemozoin) are the remnants of hemoglobin digested by the malaria parasite.
• Called Stippling: a degeneration process occurring in Plasmodium infected RBCs
• Includes Schuffner's dots, Ziemann's dots, Maurer's clefts.

Treatments

• Treatments vary by parasite stage: tissue schizonticides/blood schizonticides/gametocyticides.
• Chloroquine, primaquine, pyrimethamine, mefloquine, and artemisinin.
• Chemoprophylaxis/preventive medications for people at risk in endemic areas.

Epidemiology

• Malaria persistence requires three factors: infected humans who are gametocyte carriers, suitable Anopheles mosquito vectors, and susceptible humans.

Natural Resistance

• Some people naturally resistant due to:
  • Absence of the Duffy antigen, resistant to P. vivax.
  • Sickle cell disease. Specific hemoglobin shape and structure are not suitable environments for P. falciparum growth.
  • G6PD enzyme deficiency; Plasmodium falciparum growth needs this enzyme.

Control Strategies

• Treatment of infected individuals
• Mosquito control (vector control)
• Vaccination trials

This quiz covers the essential aspects of malaria, including the different types caused by Plasmodium species and their global distribution. Additionally, it explores the life cycle of Plasmodium and how it affects the human body. Test your knowledge on one of the world's most significant infectious diseases.