Intro Parasitology

• Parasitology is the study of the interaction between parasites and their hosts
• Parasite


  An organism that inhabits another organism, thereby deriving its nutrients from the host organism and depending on it for its survival
• Whilst most parasites are potentially hazardous, all do not produce disease since this may lead to the eradication of both the organism and host
• Exposure of an individual to an organism can lead to

  • Transiently colonize the person
  • Permanently colonize the person
  • Produce disease
• Colonization


  When an organism inhabits a person without interfering with normal body functions
• Disease


  When the interaction between microbe and human leads to a pathologic process characterized by damage to the human host
• Types of organism relationships

  • Parasitology
• Malaria is one of the major world public health problems, causing 350-500 million infections worldwide and approximately 1 million deaths annually
• How malaria is spread


  1. A mosquito infected with parasites bites you and transfers the parasite to you

  2. You can't get malaria just by being near a person who has the disease

  3. Malaria is spread when an infected Anopheles mosquito bites a person
• Taenia saginata


  The beef tape worm, a parasite (cestode) of both cattle and humans, which can only reproduce in humans
• Taenia saginata occurs where cattle is raised, human feces is improperly disposed off, meat inspection programs are poor, and where meat is eaten without proper cooking
• Two species from the Taenia genus that are common parasites of man

  • Taenia solium (the pork tapeworm)
  • Taenia saginata (the beef tapeworm)
• Improperly disposed human feces, poor meat inspection programs, and eating of improperly cooked meat are well known risk factors for the transmission of the disease
• Rarely, the worm may be present in the stomach leading to potentially infective oro-gastric secretions of these patients. Contamination with these secretions may lead to infection to the caregivers making it an unusual but important route of transmission of taeniasis, particularly in the highly endemic areas
• Ectoparasites


  True parasites that depend on the host for habitat and nutrition but live on and not in their hosts
• Endoparasites


  Parasites that live in the bodies and tissues of their hosts, some even live within the cells that make up their hosts
• Infection


  Infectious diseases are caused by transmissible organisms (biological agents) that multiply within the host
• Infestation


  When parasites do not multiply within the host, the severity of disease is often highly dependent on the infectious (or infestious) dose
• Parasitism

  • Obligate parasitism: complete dependence of the parasite on the host
  • Facultative parasitism: can switch between a parasitic and a free-living lifestyle
• The vast majority of parasites that cause human disease are obligate parasites
• The Ebers papyrus, written about 1600 BC, contains references to the presence of parasitic worms in man
• The laws of the Mosaic code prohibiting the consumption of meat from unclean animals indicate that the early Israelites had knowledge about parasitic infections
• There is evidence of parasitic recognition among the Roman, Greek, Persian, and Phoenician scientists
• Chinese doctors were aware of parasites as early as 300 BC
• The liver fluke Fasciola hepatica was discovered by Jehan de Brie from sheep


  1379
• Anton Van Leeuwenhoek described the morphology of the protozoan Giardia lamblia from his own stool


  1632-1723
• Laveran demonstrated the intracellular parasites of malaria


  1880
• Fasciola hepatica is a parasite
• There are misconceptions about parasitology
• Mode of Transmission


  Can directly transmit an infection from the main host to another host
• Mode of Transmission

  Cannot transmit directly from one host to another
• Mode of Transmission

  • Rickettsia, Taenia, etc.
  • Candida, Acanthamoeba, etc.
• Obligate Parasite


  Requires a host to survive and reproduce
• Facultative Parasite


  Can live independently or as a parasite
• The Ebers papyrus contains references to the presence of parasitic worms in man


  1600 BC
• Many people believed that lice protected children from disease and leeches were used extensively for blood letting as a cure
• For a time, intestinal parasites were thought to help in cleaning the tract of excess food and waste
• Until recently, the Chinese believed that powdered Ascaris was helpful for medicinal treatment of impotency
• In France, the heads of tapeworms (scolices) were once used as weight control measures
• Modern medicine


  Recognized the pathogenic effects of parasites and is searching for drugs useful in the treatment of parasitic infections