Protozoa and helminths

• Microorganisms


  • Water mould
  • Slime mould
  • Protozoa
  • Diatoms
  • Dinoflagellates
  • Algae
  • Green algae
• Prokaryote


  Organism without a true nucleus
• Eukaryote


  Organism with a true nucleus
• Routes of Parasitic Infections

  • Pearson Education, 2011
• Protist Groups


  • Protist
  • Protozoa
  • Protophyta
  • Molds
  • Heterotrophic/parasitic
  • Autotrophic
  • Saprophytic
  • Algae
  • Flagellata
  • Water molds
  • Slime molds
  • Ciliophora
  • Amoeba
  • Sporozoans
• Protist


  Eukaryotic organism that is not an animal, plant or fungus
• Protozoa


  • Unicellular eukaryotes
  • Non-photosynthetic
  • Animal-like behaviour
  • Motility
  • Predation
  • Microscopic (10-52µm)
  • Xenophyophore are larger (>65,000 species)
  • 'First animal' or 'little animal'
  • 200mm (Syringammina fragilissima)
• Protozoa Habitats


  • Widely distributed
  • Fresh water
  • Marine water
  • Soil
  • Aerial (trees)
  • Parasitic (animals and humans)
  • Microscope - 'animalcules' (17th Century, Antonie van Leeuwenhoek)
• Giardia duodenalis (G. lamblia, G. intestinalis)


  Protozoan parasite
• Cells vs Cysts


  Protozoa can exist in both active and dormant forms
• Protozoa Feeding


  • Bacteria / Algae
  • Protozoa
  • Larger creatures
  • "First animals"
  • Grazers
  • Hunters
  • Fungi
  • Absorb through cell membrane
  • Vacuole
• Protozoa Life Cycle


  1. Trophozoites

  2. Cysts

  3. Dormant

  4. Proliferation

  5. Drying

  6. Chemicals

  7. Lack of nutrients

  8. Outside host

  9. Transmission

  10. Encystation

  11. Excystation

  12. Binary fission

  13. Multiple fission

  14. Conjugation (sexual genetic exchange, not reproduction)
• Protozoa classification is problematic, with some genetic data and limited characteristics like locomotion and hosts
• Protozoa Movement


  • Sarcodina (pseudopodia)
  • Mastigophora (flagella)
  • Ciliophora (cilia)
  • Sporozoa (no movement)
• Entamoeba histolytica


  Parasitic amoeba, causes amoebiasis in developing countries, ingested through contaminated water/food/soil
• Entamoeba histolytica can cause asymptomatic, invasive intestinal, and invasive extra-intestinal (abscesses) infections, diagnosis is difficult and non-pathogenic Entamoeba spp. can cause false positives
• Naegleria fowleri


  Brain-eating amoeba, causes primary amoebic meningoencephalitis, found in fresh water, hot springs, soil, and swimming pools with low/non-chlorinated water
• Ciliophora (Ciliates)


  • External cilia for movement, sensing, food acquisition
  • Trophozoite stage
  • Freshwater grazers of bacteria, algae, other ciliates
  • High degree of subcellular specialisation
  • Two nuclei (micronucleus and macronucleus)
  • Inheritance and mRNA production
• Ciliate Sexual Reproduction


  1. Join at oral groove

  2. Micronuclei disintegrate

  3. Micronuclei divide by mitosis

  4. Two matching pairs

  5. Separation, one type in each

  6. Pairs fuse (vs Binary fission)

  7. No new cell produced

  8. Move to the groove
• Ciliate Examples


  • Paramecium spp. (most common)
  • Paramecium caudatum + Holospora obtusa
  • Balantidium coli (only ciliate to cause human disease, zoonotic)
• Mastigophora (Flagellates)


  • 1+ flagella for movement
  • Most species free living and mobile
  • ~1500 species
  • Inhabit fresh and marine water
  • Binary fission, some sexual reproduction (syngamy)
• Giardiasis


  Zoonotic disease caused by the flagellate Giardia, also known as 'beaver fever'
• Apicomplexa (Sporozoans)

  • Parasitic
  • Unique organelle called apicoplast, essential for cell function
  • Complex life cycles with asexual and sexual stages
  • Manufacture compounds, differentiate chlorophyll, store starch
• Plasmodium falciparum


  Causes malaria, infects ~300 million people
• Cryptosporidium Species


  • C. parvum
  • C. hominis
  • C. felis
  • C. meleagridis
  • C. canis
  • C. muris
• Cryptosporidium


  Oocysts have a tough outer shell for protection, transmitted via faecal-oral route, direct and indirect (contaminated water), resistant to chlorine
• Diarrhoea accounts for 10.5% of deaths (~840,000) in children under 5 globally, with Cryptosporidium being one of the four major pathogens causing severe diarrhoea
• Cryptosporidiosis


  Symptoms include diarrhoea, stomach pains, nausea, vomiting, fever, can infect anyone but most common in 1-5 year olds, detected by examination of stool samples, no specific treatment, recovery takes around one month
• Protozoa Classification


  • Pseudopodia
  • Cilia
  • Flagella
  • None
  • Ubiquitous
  • Multiple phases (cysts, trophozoites)
  • Many pathogenic
• Helminths are macroscopic, multicellular parasitic worms, with either monoecious (hermaphroditic) or dioecious (two sexes) adults, and infected individuals generally carry more than one
• Collective Helminths


  • Tapeworms (cestodes)
  • Flukes (trematodes)
  • Roundworms (nematodes)
  • Thorny-head worms (acanthocephalans)
• Helminth lifecycles are complex, involving intermediate hosts, and they reside in but do not replicate within humans, with climate and topography being crucial for infection
• Major Human Helminths


  • Hookworms (Necator americanus, Ancylostoma duodenale)
  • Whipworm (Trichuris trichiura)
  • Giant roundworm (Ascaris lumbricoides)
  • Roundworms
• Soil-Transmitted Helminths


  Spread through human faeces and poor sanitation, infect ~1.5 billion people
• Intestinal Worms


  • Rarely cause death, but have chronic effects like diarrhoea, abdominal pain, weakness, impaired physical and mental development
  • Cause intestinal blood loss and nutrient malabsorption, leading to anaemia and physical weakness
• Human/Helminth Co-evolution


  Leads to "disease tolerance", where helminths infect hundreds of millions asymptomatically by minimising virulence and engaging the immune system in a regulated type 2 response
• There is limited treatment available for helminths, with only 4 drugs marketed between 1975-2004, and the poor cannot afford these drugs, so potential vaccine candidates are being explored
• Nematoda (Roundworms)


  • Elongated, round and un-segmented, with a complete digestive system and highly developed separate sexes, adapted for the external environment, most human infections occur by ingestion of egg or larva
• Enterobius vermicularis (Pinworm)


  Small, thin white worm that infects ~500 million people, mainly young children, female lays eggs around the anus causing itching, transmitted via the faecal-oral route and inhalation
• Platyhelminthes (Flatworms)


  • Flattened, monoecious (hermaphroditic), two classes: Trematoda (flukes) and Cestoda (tapeworms)