Malarial Parasites in Simian and Avian Hosts

Simian Parasites

• Plasmodium species infecting monkeys/apes include P.cynomolgi, P.fragile, P.fieldi, P.hylobati, P.simiovale, and twenty others.
• These parasites share biological traits with human malaria parasites.

Avian Parasites

• Common avian Plasmodium species: P.gallinaceum, P.lophurae, P.elongatum, P.relictum, P.fallax.
• Avian parasites undergo pre-erythrocytic schizogony in the mesoderm, unlike mammals where it occurs in the liver.

Reptilian Parasites

• P.wenyoni is the sole malarial species infecting snakes.
• Malarial parasites are prevalent in lizards but not found in crocodiles.

Human Malarial Parasites

• Plasmodium vivax: Causes benign tertiary malaria with symptoms like headache, nausea, vomiting, and high fevers lasting up to a year if untreated.
• Plasmodium ovale: Similar symptoms to P.vivax; untreated lasts about a year.
• Plasmodium malariae: Causes quaternary malaria with 72-hour fever cycles; can last up to 20 years untreated.
• Plasmodium falciparum: Leads to malignant tertiary malaria and can cause severe complications like brain hemorrhage, coma, or death.

Morphological Differences

• Blood stages vary among Plasmodium species, aiding in differentiation:
  • P.falciparum: Smaller, numerous ring stages, and frequent multiple infections.
  • P.vivax: Engorged erythrocytes exhibiting Schüffner's dots; ameboid trophozoite shape with over 20 merozoites.
  • P.ovale: Similar to P.vivax but generally a more compact form.
  • P.malariae: Compact forms with formation of rosettes of merozoites (8-10 per schizont).

Characteristics of Plasmodium Species

• P.falciparum: Not enlarged host cells, dark pigment (Maurer’s dots), compact structure with multiple trophozoites.
• P.vivax: Enlarged, round/oval host cells, golden brown granules with Schüffner's dots.
• P.malariae: Regularly shaped with pigment granules, minimal modification to erythrocytes.
• P.ovale: Enlarged, round/oval host cells with James’s dots, compact morphology.

Life Cycle of Malaria Parasite

• Malaria is a digenetic parasite requiring both mosquito (definitive host) and a vertebrate (intermediate host) for its life cycle.
• The cycle includes sporogony (sexual phase in mosquitoes) and schizogony (asexual phase in vertebrates).
• Sporozoites are injected into the bloodstream during a mosquito’s blood meal and travel to the liver to begin the infection.

Exo-Erythrocytic Stages

• Infection starts with sporozoites entering the bloodstream; they have a short circulatory period before invading the liver.
• Sporozoites can die shortly after reaching the liver, particularly in Kuppfer cells.