Introduction to Parasitology

• Medical parasitology


  Deals with the parasites, which cause human infections and the diseases they produce
• Parts of parasitology


  • Protozoology
  • Helminthology
• Protozoology


  Study of protozoans
• Protozoans


  Unicellular eukaryotes (basic parasite)
• Protozoans are typically in a unit of um
• Helminthology


  Study of helminths
• Helminths


  Multicellular (large or macroparasites) eukaryotes
• Helminth life cycles are complex and have complex metabolic activities
• Helminthology is in cm or m
• Humans are


  • Of clinical significance
  • Also called host
  • Organisms that can harbor the parasites
• Hosts


  • Animals
  • Insects/Vectors
  • Plants
• Symbiosis


  Living together of unlike organisms. It may also involve protection or other advantages to one or both organisms
• Commensalism


  Symbiotic relationship in which two species live together and one species benefits from the relationship without harming or benefiting the other
• Mutualism


  Symbiosis in which two organisms mutually benefit from each other
• Parasitism


  Symbiotic relationship where one organism, the parasite, lives in or on another, depending on the latter for its survival and usually at the expense of the host
• Types of parasites


  • Obligatory parasite
  • Facultative parasite
  • Endoparasite
  • Ectoparasite
• Types of hosts


  • Accidental or Incidental host
  • Definitive host
  • Intermediate host
  • Reservoir host
  • Transport host (surface)
  • Carrier
• L1 and L2 are asexual larval stages, L3 and L4 are sexual larval stages
• Parasitic life cycle components


  • Mode of transmission
  • Infective stage
  • Diagnostic stage
• Direct life cycle


  Parasite requires only single host to complete its developments
• Indirect life cycle


  Parasite requires 2 or more species of host to complete its development
• Definitive hosts are commonly humans and intermediate hosts are animals and plants
• Sources of infection


  • Contaminated (Feces, Sputum, Blood) Soil & Water
  • Food
  • Insect Vectors
  • Animals
  • Other persons
• Modes of transmission


  • Oral transmission
  • Skin transmission
  • Vector transmission
• Oral transmission


  Transmission via contaminated food, water, soiled fingers or fomites. If the sources are through feces it is called as fecal – oral route
• Skin transmission


  Hookworms and Strongyloides enter via exposure of skin to soil, while Schistosoma species enter skin via water
• Vector transmission


  Transmission through insect bite. The parasite can enter the vector with the help of vectors penetrating the skin
• Major body areas affected by parasitic diseases


  • Gastrointestinal (GI) and urogenital (UG) tract
  • Blood and tissue
  • Liver, lung, and other major organs
  • Miscellaneous locations - cerebrospinal fluid (CSF), eye, skin, and extremities
• Parasitic disease prevention and control

  • Morbidity control
  • Environmental management
  • Environmental sanitation
• Morbidity control


  Avoidance of illness caused by infections. It may be achieved by periodically deworming individuals or groups, known to be at risk of morbidity
• Environmental management


  Planning, organization, performance, and monitoring of activities for the modification and/or manipulation of environmental factors or their interaction with human beings with a view to preventing or minimizing vector or intermediate host propagation and reducing contact between humans and the infective agent
• Environmental sanitation


  Interventions to reduce environmental health risks including the safe disposal and hygienic management of human and animal excreta, refuse, and waste water