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.

This quiz explores the various species of Plasmodium that infect simian and avian hosts. It covers the biological characteristics of these parasites and highlights their differences from those that infect humans. Test your knowledge on these fascinating organisms and their life cycles.