Medical Parasitology Final Revision Lecture

Parasites

• Ectoparasite: Lives on the outer surface of the host
• Endoparasite: Lives inside the host's body
• Temporary parasite: Lives on the host's body for a short period
• Permanent parasite: Lives on the host's body for a long period
• Reservoir host: An animal that can harbor the parasite and transmit it to other animals
• Vector: An animal that transmits the parasite to another animal or human

Helminthes

• Trematodes: Flat, leaf-like, and hermaphroditic except for Schistosoma
  • Examples: Liver Flukes (Fasciola gigantica), Intestinal Flukes (Heterophyes heterophyes), Blood Flukes (Schistosoma)
• Cestodes: Flat, segmented, and hermaphroditic
  • Examples: Taenia saginata (beef tape worm), Taenia solium (pork tape worm), Hymenolepis nana (dwarf tapeworm)
• Nematodes: Cylindrical, rounded, and separate sexes
  • Examples: Ascaris lumbricoides, Enterobius vermicularis, Ancylostoma duodenale, Trichinella spiralis

Trematodes

• Fasciola gigantica
  • Geographical distribution: Found in Egypt, particularly around the Lake Nile Valley and Delta
  • Habitat: Bile duct
  • Infective stage: Encysted metacercaria
  • Mode of infection: Ingestion with contaminated vegetation or drinking water
  • Stages in snail: Miracidium-sporocyst-redia-cercaria
• Heterophyes heterophyes
  • Geographical distribution: Found around the Lake Nile Valley and Delta
  • Habitat: Small intestine
  • Infective stage: Encysted metacercaria
  • Mode of infection: Ingestion of poorly cooked or salted fish
  • Stages in snail: Miracidium-sporocyst-redia-cercaria
• Schistosoma
  • Geographical distribution: Found in Egypt, particularly around the Lake Nile Valley and Delta
  • Habitat: Blood vessels of urinary bladder and large intestine
  • Infective stage: Furcocercus cercaria
  • Mode of infection: Penetration of skin through contaminated water
  • Stages in snail: Miracidium-sporocyst-redia-cercaria

Cestodes

• Taenia saginata
  • Shape: 10-meter long, scolex with 4 suckers
  • Definitive host: Man
  • Intermediate host: Cattle
  • Infective stage: Cysticercus bovis
  • Mode of infection: Eating undercooked beef
• Taenia solium
  • Shape: 4-meter long, scolex with suckers and rostellum
  • Definitive host: Man
  • Intermediate host: Pig
  • Infective stage: Cysticercus cellulosa
  • Mode of infection: Eating undercooked pork or auto-infection
• Hymenolepis nana
  • Shape: 5-cm long, broad segments
  • Definitive host: Man
  • Intermediate host: Insect and man
  • Infective stage: Egg and cysticercoid
  • Mode of infection: Eating infected insects or contaminated food and water
• Echinococcus granulosus
  • Shape: 5-mm long, 3-4 segments
  • Definitive host: Dog
  • Intermediate host: Sheep and man
  • Infective stage: Egg
  • Mode of infection: Eating contaminated food and water, playing with dogs, or skinning of fox

Nematodes

• Ascaris lumbricoides
  • Shape: 20-40 cm long, creamy color with 3 lips
  • Habitat: Small intestine
  • Infective stage: Larvated egg
  • Mode of infection: Contaminated food and water
• Enterobius vermicularis
  • Shape: 0.5-1 cm long, thin pointed tail in female
  • Habitat: Large intestine
  • Infective stage: Egg
  • Mode of infection: Ingestion, inhalation, person-to-person contact, and auto-infection
• Ancylostoma duodenale
  • Shape: Large mouth cavity with teeth and lancets
  • Habitat: Small intestine
  • Infective stage: Filariform larva
  • Mode of infection: Penetration of skin through contaminated soil or water
• Trichinella spiralis
  • Shape: 3-5 cm long, whip-like thin part and then a thicker portion
  • Habitat: Small intestine
  • Infective stage: Infective trichina capsule
  • Mode of infection: Ingestion of raw or undercooked pork meat containing trichina capsule

Protozoa (Single Cell Parasites)

• Entamoeba histolytica
  • Trophozoite: Finger-like pseudopodia, food and RBCs vacuoles, single cart-wheel nucleus
  • Cyst: Rounded cyst wall, chromatoid bodies, 4 cart-wheel nuclei
  • Habitat: Large intestine
  • Infective stage: Mature cyst by contaminated food or drink
• Giardia intestinalis
  • Trophozoite: Smiling face appearance, 4 pairs of flagella, 2 oval nuclei
  • Cyst: Oval cyst wall, remnant of flagella, 4 nuclei at one side
  • Habitat: Small intestine
  • Infective stage: Mature cyst by contaminated food or drink
• Entamoeba coli
  • Trophozoite: Blunt pseudopodia, no RBCs vacuole, single large eccentric nucleus
  • Cyst: Rounded large cyst, small chromatoids, 8 eccentric nuclei
  • Habitat: Large intestine
  • Infective stage: Commensal