Lecture Notes: Eukaryotes - Protozoa and Helminths

Overview

• Focus on protozoa and helminths (worms) as eukaryotic organisms.
• Protozoa are primarily found in water, but some inhabit soil.
• Only a few protozoa species are pathogenic.

Protozoa Life Forms

• Trophozoite: The active, feeding, and motile form of protozoa.
  • Causes damage to the host.
  • Example: Trichomonas vaginalis (does not have mitochondria or cyst form).
• Cyst: The dormant, protective form that can be shed and is infectious.
  • Transforms into trophozoite form in the host.

Reproduction

• Asexual: Binary fission, budding, schizogony.
• Sexual: Conjugation, seen in organisms like Paramecium.

Medically Important Protozoa

Phylum: Archaezoa

• Trichomonas vaginalis: Causes sexually transmitted infection.
  • Direct damage to epithelium, leads to micro-ulcerations.
• Giardia lamblia: Causes giardiasis via fecal-oral route.
  • Trophozoite located in small intestine; cysts excreted in feces.

Phylum: Euglenozoa

• Euglena: Non-pathogenic, photosynthetic due to chloroplasts.

Phylum: Microspora

• Entamoeba histolytica: Causes amoebic dysentery.
  • Transmitted via fecal-oral route; motile by pseudopodia.

Phylum: Apicomplexa

• Includes Plasmodium (causes malaria), Toxoplasma gondii, Cryptosporidium.
  • Complex life cycles; obligate intracellular parasites.

Phylum: Ciliophora

• Balantidium coli: Causes severe dysentery.
  • Transmitted via fecal-oral route.

Malaria and Plasmodium Lifecycle

• Mosquito Host: Anopheles mosquito transmits sporozoites via saliva.
• Human Host: Sporozoites travel to liver, develop into merozoites, infect red blood cells.
  • Rupturing RBCs releases waste causing symptoms: fever, chills, etc.
  • Sexual reproduction in mosquito, asexual in humans (intermediate host).
• Pathogenesis: Clotting and organ damage due to RBC rupture.
• Epidemiology: Millions affected annually, especially in Africa.
• Prevention: Insecticides, mosquito nets, prophylactic medications.

Hemoflagellates

• Trypanosoma brucei: Causes African sleeping sickness (tsetse fly).
• Trypanosoma cruzi: Causes Chagas disease (kissing bug).
  • Found in South/Central America, affects heart and digestive systems.

Helminths (Worms)

• Platyhelminthes (Flatworms): Includes tapeworms and flukes.
• Nematodes (Roundworms): Most common, e.g., Ascaris.

Tapeworms

• Taenia (Pork/Beef): Segmented worms with proglottids containing eggs.

Flukes

• Schistosomiasis Lifecycle: Eggs penetrate snail, release cercaria which penetrates human skin.
  • Causes inflammation and damage due to egg deposition in organs.

Conclusion of Lecture

• Recapped the life cycles, pathogenicity, and transmission of protozoa and helminths.
• Highlighted the importance of understanding the complex life cycles for effective treatment and prevention of diseases.