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• Parasites


  Organisms that live on & in other living organisms for survival
• Host


  Organisms that harbor the parasite & provide its nourishment
• Types of parasites


  • Protozoa (single-celled)
  • Helminths (worms or metazoan, multi-celled)
• Symbiont


  Specie that benefits to the detriment of the other
• Parasitism


  Parasite deprives the host of essential nutrients
• Types of parasites based on location

  • Ectoparasites (live outside of host body)
  • Endoparasites (inside the body of host)
• Infestation


  Invasion of the body by ectoparasites
• Infection


  Invasion of the body by endoparasites
• Types of parasites based on dependence

  • Obligate parasite (must exist as parasite inside a host)
  • Facultative parasite (can live independently, free-living)
• Types of parasites based on duration

  • Permanent parasites (remain in a host from early life to maturity)
  • Intermittent parasites (simply visit the host during feeding time)
  • Erratic parasites (become fixed in an unusual organ different from that which is ordinarily parasitized)
  • Aberrant parasites (wandering parasites that infect a host where they cannot develop any further)
• Types of hosts


  • Definitive host (harbors the adult or sexual stage)
  • Intermediate host (harbor larval or asexual stage)
  • Paratenic host (serve as means of transport, e.g. vectors)
  • Reservoir host (vertebrate hosts which harbor the parasite and act as a source of infection in humans)
  • Dead-end host (parasite cannot complete its life cycle)
• Types of protozoa


  • Sporozoa (no movement)
  • Sarcodina (amoebas, no feet)
  • Mastigophora (flagellates, have flagella)
  • Ciliata (ciliates, have cilia)
• Entamoeba histolytica


  Causes amebiasis, flask-shaped ulcer
• Balantidium coli


  Causes balantidiasis, dysenteric diarrhea
• Toxoplasma


  Causes toxoplasmosis, meningoencephalitis
• Acanthamoeba


  Causes meningoencephalitis
• Naegleria


  Causes meningoencephalitis
• Giardia lamblia


  Causes giardiasis, steatorrhea ("fat in the stool")
• Main reservoir for Balantidium coli is the pig
• Definitive host for Toxoplasma is the cat
• Modes of transmission for protozoan parasites

  • Ingestion of contaminated food
  • Ingestion of contaminated water
  • Sexual route
• Protozoan parasitic diseases


  • Leishmaniasis (visceral, cutaneous, mucocutaneous)
  • Chagas' disease (American trypanosomiasis)
  • African sleeping sickness
  • Malaria
• Vectors for protozoan parasites

  • Sand fly
  • Reduviid bug (kissing bug)
  • Tsetse fly
  • Anopheles mosquito
• Modes of transmission for protozoan parasites

  • Bite of vector
• Metazoa


  Worms or helminths
• Types of helminths


  • Platyhelminthes (flatworms, including cestodes and trematodes)
  • Nematodes (roundworms)
• Cestodes


  Tapeworms, flat worms with two main parts: scolex (rounded, contains structures for attachment) and body (proglottids)
• Cestodes


  • Worm grows by adding proglottids from the neck
  • Each proglottid (gravid segment) has both male and female reproductive organs
  • Oldest proglottids are found at the most distal part of the parasite
  • Eggs are excreted in feces and transmitted to intermediate hosts (cattle, pigs, fish)
• Taenia saginata


  Beef tapeworm, acquired by ingestion of raw or improperly cooked beef containing infective larvae (cysticercus)
• Taenia solium


  Pork tapeworm, can disseminate to eyes, brain, skeletal muscles, causing cysticercosis
• Diphyllobothrium latum


  Fish tapeworm, longest of all tapeworms, up to 13 meters, causes megaloblastic anemia (vitamin B12 deficiency)
• Hymenolepis nana


  Dwarf tapeworm, eggs are directly infectious, no obligatory intermediate host, can cause autoinfection and hyperinfection syndrome
• Echinococcus granulosus


  Dog tapeworm, primarily a zoonotic parasite, can cause hydatid cyst in humans, rupture of cyst can lead to anaphylaxis
• Summary of cestodes (tapeworms)

  • Taenia saginata (beef tapeworm)
  • Taenia solium (pork tapeworm)
  • Diphyllobothrium latum (fish tapeworm)
  • Hymenolepis nana (dwarf tapeworm)
  • Echinococcus granulosus (dog tapeworm)
• Trematodes


  Flukes, flat, fleshy, leaflet-shaped worms with a digestive tract and two muscular suckers (oral and ventral)
• Most flukes are hermaphroditic, except for Schistosoma species (blood flukes)
• Most flukes have two intermediate hosts, except for Schistosoma species (one intermediate host)
• Schistosoma


  Blood fluke, not hermaphroditic, obligate intravascular parasite, infective stage is cercaria
• Schistosomiasis (Bilharziasis)


  Disease caused by Schistosoma, early infection causes rash, pruritic papules, fever, chills, diarrhea, lymphadenopathy
• Schistosoma japonicum


  Oriental blood fluke, reservoir is domestic animals, causes Katayama's disease, liver dysfunction, portal hypertension, risk of liver cancer