Sporozoa

• Sporozoa


  Formerly known as Apicomplexa, have an apical complex at the anterior end, have an alternating sexual and asexual life cycle
• Important groups of Sporozoa

  • Plasmodia
  • Babesia
  • Toxoplasma
  • Sarcocystis
  • Cytoisospora
  • Cryptosporidium
  • Cyclospora
• Sporozoa


  • Have been reported from all organ systems of humans and animals: gastrointestinal tract, genitourinary tract, central nervous system, respiratory tract, reticuloendothelial system, blood and blood cells, eyes, skin, oral cavity
• Sporozoa categorized according to

  • Blood
  • Intestinal
  • Tissue
• Blood Sporozoa


  • Plasmodium spp.
  • Babesia
• Intestinal Sporozoa


  • Cytoisospora (Isospora) belli
  • Cryptosporidium spp.
  • Cyclospora cayatinensis
• Tissue Sporozoa


  • Toxoplasma gondii
  • Sarcocystis
• Plasmodium spp.


  Causes malaria, mostly affect young children and pregnant women, children - anemia, pregnancy - anemia and cardiac failure, parasites are found in erythrocytes and hepatocytes
• Plasmodium spp. include


  • P. falciparum
  • P. vivax
  • P. ovale
  • P. malariae
  • P. knowlesi
• Plasmodium spp.


  • P. vivax is predominant in most parts of the world, P. falciparum is mostly confined to the tropics and subtropics, P. malariae occurs in subtropical and temperate, is less frequently seen than P. vivax or P. falciparum, P. ovale is confined to West Africa, P. knowlesi is a monkey malaria distributed in Southeast Asia
• Life Cycle of Plasmodium spp.

  1. Completed in 2 hosts: definitive host - female Anopheles mosquito, intermediate host - humans

  2. Modes of transmission: bite of infected mosquito, blood transfusion, congenital transmission, shared syringes
• Life Cycle of Plasmodium spp.

  1. Asexual Multiplication (Schizogony) occurs in intermediate hosts: sporozoites to hepatocytes (exoerythrocytic/pre-erythrocytic schizogony), merozoites to erythrocytes (erythrocytic schizogony)

  2. Sexual Multiplication (Sporogony) occurs in definitive host: gametocytes to sporozoites
• Human Cycle (Schizogony)


  Humans acquire infection from bites of infective female Anopheles mosquito, sporozoites in salivary gland injected into capillaries, sporozoites circulate in blood and enter hepatocytes
• Exoerythrocytic Cycle


  1. Sporozoites reach hepatocytes and initiate schizogony, schizonts/meronts to merozoites, P. vivax and P. ovale can have dormant schizonts (hypnozoites) that can cause relapse

  2. Pre-patent period: interval between entry of sporozoites and appearance of parasite in blood
• Erythrocytic Cycle


  Merozoites invade RBCs and form ring stage trophozoites, parasite feeds on hemoglobin and forms hemozoin, develop into schizonts that rupture (febrile paroxysms) and infect other RBCs, differentiate into gametocytes
• Erythrocytic Cycle


  Incubation period: interval between entry of sporozoites and earliest manifestation of clinical illness, in P. falciparum erythrocytic schizogony occurs in capillaries and vascular beds of internal organs
• Sporogonic Cycle


  Occurs after female Anopheles mosquito ingests parasitized erythrocytes, gametocytes undergo further development in mosquito midgut, zygote develops into ookinete, ookinete penetrates stomach epithelia, oocyst forms with numerous sporozoites, oocyst ruptures and releases sporozoites into salivary glands
• Plasmodium vivax


  • Most common in Asia and America, causes benign tertian malaria, cycle every 48 hours, merozoites infect reticulocytes and young erythrocytes, all stages visible in peripheral smear, RBC inclusion: Schuffner's dots
• Ring form of P. vivax


  • Actively motile, 1/3 of cell diameter, heavy chromatin dot
• Developing Trophozoites of P. vivax

  • Appear amoeboid, possess Schuffner's dots
• Schizonts of P. vivax

  • Contain 12-24 merozoites, fill the entire RBC
• Gametocytes of P. vivax

  • Appear relatively large, appear spherical
• Plasmodium falciparum


  • Most pathogenic, often fatal, infect both young and old erythrocytes, cause malignant tertian/pernicious malaria, cycle every 36-48 hours, RBC inclusions: Maurer's clefts, only ring forms and gametocytes visible in peripheral blood
• Ring Forms of P. falciparum

  • Appear thin and delicate, approx. 1/5 of RBC diameter, may possess 1 or 2 chromatin dots, often found on periphery of RBC (accolé or appliqué)
• Developing Trophozoites and Schizonts of P. falciparum

  • Not normally seen in peripheral blood except in severe cases, have Maurer's clefts, mature schizont has 8-24 merozoites, erythrocytic schizogony takes 36-48 hours
• Gametocytes of P. falciparum

  • Characteristic crescentic, sickle, sausage, or banana shape
• Plasmodium malariae


  • Causes quartan malaria, cycle every 72 hours, recrudescence may be provoked by splenectomy or immunosuppression, attacks old/senescent RBCs, RBC inclusions: Ziemann's dots/stipplings, few ring forms and mostly mature trophozoites and schizonts visible in peripheral blood
• Ring Forms of P. malariae


  • Usually have one chromatin dot, ring appears thicker than P. falciparum, characteristic "bird's eye" form, resemble P. vivax but cytoplasm is thicker, Ziemann's stippling may be seen
• Developing Trophozoites of P. malariae

  • Characteristic band form or basket form, some may appear distorted
• Schizonts of P. malariae

  • Have a rosette/daisy head/irregular appearance, fill the entire RBC, usually filled with 8 merozoites, erythrocytic schizogony takes 72 hours
• Gametocytes of P. malariae

  • Appear compact and tend to fill the host RBC
• Plasmodium ovale


  • Causes tertian fever, cycle every 48 hours, resembles P. vivax except milder symptoms, prolonged latency, fewer relapses, rarest of all plasmodia, attack young RBCs, RBC inclusions: Schuffner's/James' dots, all stages visible in peripheral blood
• Ring Forms of P. ovale


  • Usually contain a single chromatin dot, multiply-infected RBCs may be seen, larger and more ameboid than P. vivax
• Developing Trophozoites of P. ovale

  • Infected RBCs have characteristic fimbriations and serrated edges, appear enlarged
• Schizonts of P. ovale

  • Similar to P. vivax but smaller, have lesser merozoites
• Gametocytes of P. ovale


  • Difficult to distinguish from P. vivax, less enlargement of infected RBC
• Plasmodium knowlesi


  • Causes quotidian fever, cycle every 24 hours, normally a parasite of long-tailed macaques, humans working in nearby forest fringe pose great risk for infection
• Ring Forms of P. knowlesi


  • Resembles P. falciparum, accolé form, double chromatins and multiple infections common in infected RBC
• Developing Trophozoite of P. knowlesi

  • Has a band form resembling P. malariae
• Schizont of P. knowlesi

  • Has an average of 10 merozoites, with a maximum of 16, erythrocytic schizogony takes 24 hours