PARASIT 2

• Symbiosis


  Living together of unlike organisms
• Commensalism


  Symbiotic relationship where one species benefits without harming or benefiting the other
• Mutualism


  Symbiosis where 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
• Commensal

  Association between two different organisms where one benefits and has a neutral effect on the other
• Pathogenic


  Parasite that has demonstrated the ability to cause disease
• Types of parasites


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


  • Accidental or incidental host
  • Definitive host
  • Intermediate host
  • Reservoir host
  • Transport host
  • Carrier
• Exposure


  Process of inoculating an infective agent
• Infection


  Establishment of the infective agent in the host
• Incubation period


  Period between infection and evidence of symptoms
• Pre-patent period

  Period between infection/acquisition of parasite and evidence of infection
• Autoinfection


  Infected individual becomes their own direct source of infection
• Superinfection or hyperinfection


  Already infected individual is further infected with the same species leading to massive infection
• Sources of parasitic infections

  • Contaminated soil and water
  • Lack of sanitary toilets
  • Use of night soil or human excreta as fertilizer
  • Water and food containing infective stage of parasite
  • Consumption of undercooked or raw freshwater fish
  • Arthropods
  • Other animals
  • One's self
• Modes of transmission


  • Direct (droplet spread, sexual intercourse, kissing, holding hands, transplacental/vertical)
  • Indirect (ingestion of contaminated food & drink, contact with contaminated soil, bite of infected arthropod, through fomites)
• Most common source of parasitic infection is contaminated food and water, with the mouth being the most likely portal of entry
• Skin penetration is another route of transmission for hookworms, Strongyloides, and Schistosoma species
• Arthropods serve as vectors and transmit parasites through their bites
• Congenital transmission can occur, e.g. Toxoplasma gondii trophozoites crossing the placental barrier
• Transmammary infection with Ancylostoma and Strongyloides can occur through the mother's milk
• Other ways of acquiring infection include inhalation of airborne eggs of Enterobius, and sexual intercourse as in the case of Trichomonas vaginalis
• Parasitic life cycle


  Involves a mode of transmission, an infective stage that invades humans, and a diagnostic stage that can be detected in the lab
• Major body areas associated with parasitic disease processes


  • Gastrointestinal and urogenital tracts
  • Blood and tissue
  • Liver, lung, and other major organs
  • Miscellaneous locations (cerebrospinal fluid, eye, skin, extremities)
• Commonly observed parasitic infection symptoms


  • Diarrhea
  • Fever
  • Chills
  • Abdominal pain
  • Abdominal cramping
  • Elephantiasis
  • Anemia
  • Vitamin deficiency
  • Bowel obstruction
  • Edema
  • Organ enlargement
  • Skin lesions
  • Blindness
• Preventive measures against parasitic infections

  • Education programs
  • Use of insecticides and other chemicals
  • Protective clothing
  • Protective netting
  • Proper water treatment
  • Good personal hygiene
  • Proper sanitation practices
  • Proper handling and preparation of food
  • Avoidance of unprotected sexual relations
• Eradicating parasites is an ongoing process and a key goal of international health groups like the World Health Organization
• Specimens for parasitic infection diagnosis


  • Stool
  • Urine
  • Sputum
  • Blood
  • Cerebrospinal fluid
  • Tissue aspirates (liver, duodenal, broncho-alveolar lavage)
  • Orifice swabs (vaginal, perianal)
  • Tissue biopsy (muscle, rectal)
• Blood sample processing methods


  • Blood films (fresh, thin dry, thick dry)
  • Stains (Giemsa, Wright's, Leishmann, Field's, Acridine orange, Jaswant Singh Battacharya)
  • Permanent stains and other stains (Iron Hematoxylin, MIF, Chlorazol Black E, Modified Kohn's)
• Field's stain A


  Methylene blue and Azure 1 dissolved in phosphate buffer solution
• Field's stain B


  Eosin Y in buffer solution
• Acridine orange


  Fluorescent staining agent to detect the presence of malaria parasite in blood cultures and other bodily fluids
• Acridine orange


  • It is a fluorochrome dye that can interchalate into nucleic acid
• Jaswant Singh Battacharya (JSB) Stain


  Standard method used by laboratories under the National Malaria Eradication Programme in India
• Iron Hematoxylin Stain


  Used for most of the original morphological descriptions of intestinal protozoa found in humans
• MIF Fixative Stain


  Diagnosis of Trichomonas
• Chlorazol Black E


  An acid dye, used as a fat and general tissue stain, and to stain protozoa in fecal smears or in tissues
• Modified Kohn's


  Modification of the chlorazol black E staining technique
• Wheatley Trichrome


  All-purpose (amoebae, flagellates)
• Thick Blood Film


  1. Infected erythrocytes are counted in relation to a predetermined number of WBCs

  2. Standard: average of 8000/µl

  3. All parasite species and forms (sexual and asexual) are counted