INTRO TO PARASITOLOGY

• Symbiosis


  A relationship where unlike organisms exist together
• Types of symbiotic relationships


  • Commensalism
  • Mutualism
  • Parasitism
• Commensalism


  A form of symbiotic relationship in which two species live together, and one species benefits from the other without harming or benefiting the other
• Mutualism


  A symbiotic relationship in which two organisms mutually benefit from one another
• Parasitism


  The form of symbiotic relationship where one party or symbiont (parasite) benefits to the detriment of the other (host)
• In most cases of parasitic relationship, the parasite deprives the host of essential nutrients and cause disease in the host
• Parasite


  Organisms that usually depend on the host for survival
• Ways parasites are classified

  • Based on habitat
  • Based on ability to live independently of the host
  • Based on mode of living
• Ectoparasites


  Parasites that live outside the host's body
• Ectoparasites


  • Fleas, lice
• Endoparasites


  Parasites that live inside the body of the host
• Endoparasites


  • Helminths or worms
• Infection


  Invasion of the body by the endoparasites, which is the result of entry and multiplication of the parasite within the host
• Facultative parasites


  Parasites that can live independently of the host (free living). These parasites do not have to live inside a host to complete their life cycle
• Obligate parasites


  Parasites that must live inside a host
• Obligate parasites


  • Plasmodium, Leishmania, hookworms
• Majority of the parasites that infect humans are obligate parasites
• Permanent parasites


  Parasites that remain in a host from early life to maturity
• Intermittent parasites


  Parasites that simply visit the host during feeding time
• Incidental parasites


  Parasites that occur in an unusual host
• Transitory parasites


  Parasites whose larvae develops in a host while the adult is free-living
• Erratic parasites


  Parasites that are seen in an unusual organ, different from that which it ordinarily parasites
• Host


  Organisms that harbor the parasite and provide nourishment to the parasite
• Types of hosts


  • Definitive hosts
  • Intermediate hosts
  • Reservoir hosts
  • Paratenic hosts
• Definitive hosts


  Hosts that harbor the adult stage of the parasite or where the sexual stage or sexual phase of the life cycle of the parasite occurs
• Definitive hosts


  • Humans for the intestinal round worm Ascaris
  • Mosquito for the malaria parasite Plasmodium
• Intermediate hosts


  Hosts that harbor the larval stage of the parasite or where the asexual stage of the life cycle of the parasite occurs
• Intermediate hosts


  • Cow for the cysticercus larva of the beef tapeworm Taenia saginata
  • Humans for the malaria parasite Plasmodium
• Reservoir hosts


  Vertebrate hosts that harbor the parasite and may act as an additional source of infection in man
• Paratenic hosts


  Hosts that serve as a means of transport for the parasite so that the infective stage of a certain parasite may reach its final hosts
• Sources of exposure to infection or infestation

  • Contaminated soil or water
  • Food containing the parasites infected stage
  • Blood sucking insect
  • Domestic or wild animal harboring the parasite
  • Another person and his/her clothing, bedding, or the immediate environment he/she has contaminated
  • One's self (auto-infected)
• Contaminated soil or polluted with human feces is the most common source of exposure to infection for most parasitic worms and helminths
• Contaminated water may contain viable cysts of parasitic amoebae and intestinal flagellates, tapeworm eggs, or blood flukes
• Freshwater fish serves as the source for the fish tapeworm and other intestinal and liver flukes
• Raw pork is the source of Trichinella spiralis and T. solium
• Improperly cooked or raw beef is the source of T. saginata
• Blood-sucking insects transmit malaria parasites, leishmaniasis, trypanosomes, and filariasis
• Dogs are a direct source of infection with hydatid cyst or Echinococcus granulosus
• Humans are the source of infection for Entamoeba histolytica, pinworm, and dwarf tapeworm
• Auto-infection can occur with Strongyloides stercoralis