Sarcodina and Amoeba Overview

Sarcodina (Amoebozoa)

• Sarcodina are protozoans with a thin protoplasmic membrane and no defined shape
• They move and feed using pseudopodia
• Sarcodina can be free-living, commensal or parasitic
• Amoeba proteus is an example of a free-living Sarcodina
• Amoeba proteus lives in well-oxygenated freshwater habitats, often on decaying vegetation

Amoeba proteus

• Amoeba proteus uses contractile vacuoles to regulate water through osmosis
• Amoeba proteus uses temporary pseudopodia to move and capture food
• Amoeba proteus exhibits amoeboid movement, a process where the colloidal protoplasm transitions from a fluid state ("sol") to a more solid state ("gel")

Parasitic Amoebae

• There are six genera of parasitic amoebae
• These parasites live in the intestinal tract (five genera) and the buccal cavity (one genus)

Entamoeba coli

• Entamoeba coli is an intestinal commensal
• Entamoeba coli feeds on bacteria

Entamoeba histolytica

• Entamoeba histolytica is an intestinal parasite
• Entamoeba histolytica feeds on tissues and blood of the host
• Entamoeba histolytica can cause amoebic dysentery

Entamoeba gingivalis

• Entamoeba gingivalis is a buccal commensal

Comparing Entamoeba histolytica and Entamoeba coli

• Entamoeba coli lives in the lumen of the large intestine, while Entamoeba histolytica lives in the wall of the large intestine
• The ectoplasm and endoplasm are not clearly differentiated in Entamoeba coli, but are well differentiated in Entamoeba histolytica
• Entamoeba coli has two pseudopodia, while Entamoeba histolytica has a large single pseudopodium
• The karyosome in Entamoeba coli is lateral, while the karyosome in Entamoeba histolytica is central
• Entamoeba coli has irregularly distributed chromatin granules, while Entamoeba histolytica has regularly distributed chromatin granules
• Entamoeba coli food vacuoles contain bacteria, while Entamoeba histolytica food vacuoles contain red blood cells (RBCs)
• Entamoeba coli precysts can be round or oviod in shape
• Entamoeba coli precysts lack a cystic wall
• Entamoeba coli cysts contain glycogen and rod-shaped chromatoid bodies, while Entamoeba histolytica cysts contain glycogen but lack chromatoid bodies
• Entamoeba coli mature cysts have 8 nuclei, while Entamoeba histolytica cysts have 4 nuclei

Phylum Apicomplexa

• Apicomplexa are protozoan parasites that are endoparasites in higher animals
• They are intracellular blood parasites found in blood cells and tissues of birds and mammals
• Apicomplexa cause a variety of diseases
• Apicomplexa are transmitted by blood-sucking arthropods which act as intermediate hosts

Plasmodium sp.

• There are four species of Plasmodium that infect humans
• Each species is responsible for a different type of malaria
• The four species are:
  • Plasmodium vivax
  • Plasmodium malariae
  • Plasmodium ovale
  • Plasmodium falciparum
• Each species infects red blood cells (erythrocytes) in humans
• Plasmodium can also infect white blood cells (leukocytes)

Life Cycle of Plasmodium sp.

• The life cycle of Plasmodium sp. is divided into three phases:
  • Exerythrocytic cycle (Liver stage)
  • Erythrocytic cycle (Human blood stage)
  • Mosquito stage

Exerythrocytic Cycle

• The exerythrocytic cycle takes place in the liver of humans
• The cycle starts as a sporozoite injected by the mosquito
• The sporozoite develops into a merozoite, which then infects red blood cells (erythrocytes)

Erythrocytic Cycle

• The merozoite multiplies rapidly in red blood cells by schizogony
• This creates a new generation of merozoites that are then released into the bloodstream
• These merozoites can infect other red blood cells, repeating the cycle and causing malaria symptoms

Mosquito Stage

• Mosquitoes become infected by consuming human erythrocytes containing merozoites
• Within the mosquito, the merozoites develop into gametocytes
• Gametocytes then fuse together to form zygotes
• The zygotes undergoes sporozoite formation, creating sporozoites which are then injected into humans by the mosquito
• The sporozoites then infect the liver, restarting the exerythrocytic cycle

Plasmodium sp. Transmission

• The final host of Plasmodium is the female Anopheles mosquito
• Humans are the intermediate host

Malaria

• Malaria is caused by parasites of the genus Plasmodium that are transmitted by infected female Anopheles mosquitoes
• Malaria is a serious illness that can be fatal
• Symptoms include fever, chills, sweating, headache, muscle aches, and fatigue
• Malaria is preventable and treatable