parasitology & protozoa

• Parasitology


  The study of parasites

  
• Parasitism


  A form of symbiosis in which one organism (called parasite) benefits at the expense of another organism usually of different species (called host)
• Symbiosis


  A relationship where unlike organisms exist together
• 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 each other
• Parasitism


  A form of symbiotic relationship where one party or symbiont (e.i., parasites) benefits to the detriment of the other party (host)
• Hosts


  Organisms that harbor the parasite and provide nourishment to them
• Parasites


  Organisms that usually depend on the host for survival and growth
• Types of Hosts


  • Definitive Hosts
  • Intermediate Hosts
  • Reservoir Hosts
  • Paratenic Hosts
• Classification of Parasites (Based on Habitat)

  • Ectoparasites
  • Endoparasites

  
• Classification of Parasites (Based on ability to live independently of the host)

  • Facultative parasites
  • Obligate parasites

  
• Classification of Parasites (Based on mode of living)

  • Permanent parasites
  • Intermittent parasites
  • Incidental parasites
  • Transitory parasites
  • Erratic parasites

  
• Sources of Exposure to Infection or Infestation

  • Contaminated soil or water
  • Food containing the parasite's infective stage
  • A blood-sucking insect
  • A domestic or wild animals harboring the parasite
  • Contaminated clothing, beddings, or immediate environment the person has infected
  • Auto-infection

  
• Modes of Transmission


  • Oral-fecal route
  • Skin penetration
  • Insect bites
  • Eggs inhalation
  • Transplacental or congenital infections
  • Transmammary infection
  • Sexual intercourse

  
• Portal of Exit of Parasites

  • Anus (feces)
  • Ureter (urine)
  • Lungs (phlegm)
  • Vaginal discharges
• Pathogenesis of Parasites


  • Trauma or physical damage
  • Lytic necrosis
  • Stimulation of host tissue reaction
  • Toxic & allergic phenomena (immunopathology)
  • Opening of pathways for entry of other pathogens into the tissues

  
• General Life Cycle of Parasites includes: Source of infection, Mode of Transmission, Infective Stage, Pathogenic Stage, Diagnostic Stage

  
• Classification of Parasites (Sub-Kingdom)

  • Single-celled (Protozoa)
  • Multicellular Metazoa (Helminths)

  
• Classification of Protozoa


  • Amoeba
  • Flagellates
  • Sporozoa
  • Ciliates

  
• Classification of Helminths


  • Nematodes
  • Cestodes
  • Trematodes
• Most parasitic protozoa reproduce by binary fission except sporozoa (reproduce sexually and asexually)
• Biologic, Morphologic and Physiologic Characteristics of Parasites

  • Protozoa: Amoeba, Flagellates, Ciliates, Sporozoa
  • Helminths: Cestodes, Trematodes, Nematodes

  
• Laboratory Diagnosis of Parasitic Infections

  • Specimen Collection and Processing
  • Sample Types and associated parasites

  
• Parasite


  Can distort their morphology
• Stool should be free of urine
• Stool samples for parasite detection

  • Liquid stools best for trophozoites detection
  • Formed stool for cyst and ova detection

  
• Stool preservatives


  • Stool should not be preserved for longer hours
  • 5 to 10% formalin for concentration procedures
  • PVA for stained smear preparation
  • Sodium Acetate Formalin for concentration procedures and stained smear preparation
• Fecal Concentration Methods


  • Formalin-Ethyl Acetate Sedimentation
  • Zinc Sulfate Flotation
  • Sheather Sugar Flotation
• Collection Methods


  • Cellophane / Scotch tape method (pinworm)
  • Entero Test – string test
  • Sigmoidocopy – to collect colon material
• Sample Types and associated parasites

  • Feces: Gardia, Cryptosporadium, Entanoeba, Ascaris, Enterobius, etc
  • Blood: Plasmodium, Leishmania, Trypanosoma, Microfilariae
  • Skin: Onchocerca
  • Vaginal or urethral: Trichomonas
  • Eye scraping: Acanthamoeba
  • Tissue: Naegleria, Acanthamoeba, & Leishmania
  • Urine: Schistoc=soma & Trichomonas
  • Sputum: Ascaris & Strongyloides

  
• Direct wet preparation or direct wet mount

  To detect the presence of motile protozoan trophozoites; other stages detected include cysts, oocysts, ova and larvae of worms

  
• A small portion of unfixed stool is mixed w/ saline or iodine then studied under the microscope
• Concentration Methods


  • Can be used on both fresh and preserved specimens, can detect cysts, oocysts and larvae of nematodes
  • To aggregate parasites present into a small volume of the sample that enables the detection of small numbers of parasites that might not be detected in direct wet preparation
  • To remove debris and other contaminants that might interfere with the microscopic examination

  
• Sedimentation (Formalin-Ethyl Acetate Sedimentation Procedure)

  Based on the specific gravity- parsites are heavier than the solution than the fecal debris
• Zinc Sulfate Floatation Technique


  Based on the differences in specific gravity and the sample debris (heavier than the parasites). The zinc sulfate has a specific gravity of 1.18 – 1.20 and is used as the concentrating solution
• Permanent Stains


  Serves as a final step in the microscopic examination for the detection of parasites. It is designed to confirm the presence of cysts and/ or trophozoites of protozoans

  
• Duodenal Material


  • This may be collected using nasogastric tube (NGT) or through the enteric capsule test (Entero test)
  • The collected fluid must be examined immediately to prevent rapid deterioration of trophozoites, if there is any. Less than 2ml volume is recommended for this procedure. The sample undergoes centrifugation prior to microscopic examination of the sediments
  • In the Entero- test, patient is advised to swallow gelatin capsule that cointains a coil of yarn that is weighted, which will be released to the duodenum as the capsule dissolves in the stomach. The free end of the yarn is attached to the neck or cheek of the patient and pulled out after 4 hours of incubation. The bile stained material attached to the string is then examined under the microscope by wet preparation followed by permanent stain application
• Sigmoidoscopy Material


  This is done by examination of the colon and collection of the material, which can be used in biopsy examination. It is helpful in the diagnosis of Entamoeba histolytica infection

  
• Cellophane tape or Scotch Tape Preparation

  • This is done to detect the presence of pinworm, Enterobius vermicularis. The female parasite migrates to the anus and lays it eggs
  • Done in the morning before defacation or washes
  • Used to detect tapeworm eggs of Taenia spp

  
• Blood


  • For blood-borne parasites (leishmania, trypanosoma, plasmodium and filarial worms)
  • Thin (spp identification) and thick (number) blood smear, blood from earlobe or fingertip
  • Stain used: wright's or giemsa