PPT 2 Flashcards
Give one example of a pathogenic parasite and what does it cause.
Entamoeba histolytica (causes amoebiasis)
Give one example of a commensal parasite.
Entamoeba coli
What region can parasites be mostly found in?
Tropical
What are the factors affecting distribution of parasites
a) Host Availability & Food Habits
b) Parasite Escape Mechanisms
c) Environmental Factors
d) Presence of Vectors or Intermediate Hosts
Some parasites only infect specific hosts.
• Ancylostoma duodenale → Infects humans (causes hookworm disease).
• Ancylostoma caninum → Infects dogs.
• Diet affects risk of infection:
• Eating raw or undercooked meat → Taenia saginata (beef tapeworm) or Taenia solium (pork tapeworm).
• Drinking contaminated water → Giardia lamblia (causes giardiasis).
• Some parasites spread easily through waste:
• Ascaris lumbricoides (roundworm) → Eggs are shed in feces, spreading through poor sanitation.
• Others require direct body contact or vectors:
• Plasmodium (causes malaria) → Requires mosquito bite for transmission.
• Temperature, humidity, and water presence affect survival.
• Example: Schistosoma spp. (blood flukes) → Larvae live in freshwater before infecting humans through skin contact.
• Some parasites require vectors:
• Trypanosoma brucei (causes African sleeping sickness) → Spread by tsetse fly.
• Leishmania (causes leishmaniasis) → Spread by sandflies.
• Others spread without vectors and are more widespread:
• Enterobius vermicularis (pinworm) → Spread by direct human contact.
• Simple Life Cycle (Direct Transmission)
• Involves one host.
• Example: Enterobius vermicularis (pinworm)
• Eggs ingested → hatch in intestines → lay eggs near the anus → spread via contaminated hands/surfaces.
• Complex Life Cycle (Requires Intermediate Hosts)
• Involves multiple hosts or vectors.
• Example: Plasmodium (malaria parasite)
• Mosquito bite injects parasite → infects human liver → multiplies in blood → another mosquito bites and picks up the parasite → cycle repeats.
a) Protozoa (Single-Celled Parasites)
• Microscopic organisms with various movement methods.
• Examples:
• Entamoeba histolytica → Causes amoebic dysentery (diarrhea with blood).
• Giardia lamblia → Causes giardiasis (severe diarrhea).
• Plasmodium spp. → Causes malaria.
b) Helminths (Worm Parasites)
• Multicellular organisms.
• Examples:
• Ascaris lumbricoides → Roundworm that causes intestinal blockage.
• Taenia solium → Tapeworm from pork that can invade the brain (neurocysticercosis).
• Schistosoma → Blood fluke that causes schistosomiasis (liver and bladder damage).
c) Arthropods (Insects & Mites as Parasites or Vectors)
• Some directly infest humans, others transmit parasites.
• Examples:
• Direct Infestation: Sarcoptes scabiei (causes scabies, intense itching from mites burrowing into skin).
• Vector Role:
• Anopheles mosquito → Transmits malaria (Plasmodium).
• Tsetse fly → Transmits African sleeping sickness (Trypanosoma brucei).
- Transmission of Parasites
a) Direct Contact
• Skin-to-skin transmission.
• Example: Scabies (caused by Sarcoptes scabiei).
b) Ingestion (Food/Water Contamination)
Example: Giardia lamblia from contaminated water.
c) Vector-Borne Transmission
Example: Plasmodium (malaria) via mosquito bites.
d) Penetration through Skin
Example: Schistosoma larvae enter through skin contact with contaminated water.
