Parasitology

• What is a parasite?

  An organism that lives in (endoparasite) or on (ectoparasite) another host to its own advantage , disadvantages the host
• How are parasites classified according to habitat?

  1. Endoparasite: living within host's body (e.g. intestinal worms, Schistosoma )
  2. Ectoparasite: parasite living on / affecting the skin surface of the host (e.g. ticks, lice )
• How are parasites classified according to dependence on host?

  1. Obligate: can't complete life cycle w/o spending some time in parasitic relationship
  2. Facultative: not normally parasitic (e.g. free-living nematodes - rare human infection)
  3. Incidental: parasite attaches / enters body of a species different from its normal one
• How are parasites classified according to pathogenicity?

  1. Pathogenic: causes severe diseases in host
  2. Opportunistic: cause mild disease in immunologically healthy individuals, but cause severe disease in immuno-deficient hosts
• What are the 4 types of hosts?

  1. Definitive: host in which the parasite reaches sexual maturity
  2. Intermediate: host required for completion of life cycle, but parasite doesn't sexually mature
  3. Paratenic: host in which parasite doesn't undergo any development, but it remains alive and infective to another host
  4. Reservoir: animal that harbours an infection that can be transferred to humans
• Direct life cycle

  • parasite completes life cycle in a singular host
  • infective stage (e.g. ovum, larva, cyst) is passed out of the body and infects other hosts
  • paratenic hosts
• Indirect life cycle

  • multiple hosts or involvement of a vector
  • definitive or intermediate host
• What is a vector?

  • Carrier
  • transmission of parasite
  • no direct damage by vector
• What is host specificity?

  1. absolute host specificity : parasite can only mature in one species of host
  2. definitive hosts : parasite can mature in almost any species of a class
• What is the malaria parasite and vector used?


  The parasite is plasmodium falciparum which is a protozoa (unicellular) and the vector are anopheles mosquitos (females only)
• What are the malaria treatments?

  Artemisinin paired with: Chloroquine or Amodiaquine or Mefloquine
• Life cycle (Plasmodium spp.)

  1. parasite injected into body from mosquitoes as sporozoites
  2. enters liver cells, multiplying by asexual reproduction - now are merozoites
  3. enters into RBCs , causing decreased oxygen capacity
  4. some develop into gametocytes and become fertlised
• Symptoms of malaria?


  Fever, chills, headache, muscular fatigue and pain, back pain, dry cough, enlarged spleen, nausea, vomiting
• Diagnostic techniques for protozoan parasite disease (e.g. malaria)?


  Blood smear and microscopy
• Preparing blood smear for parasite diagnosis?

  1. use separate slides for thick + thin smears
  2. thin film: clean spreader slide @ 45° angle towards drop of blood
  3. wait until blood spreads along entire width of spreader slide
  4. hold spreader slide at the same angle and push it forward smoothly and raplidly
  5. thick film: using corner of clean slide, spread drop of blood in a circle the size of a dime - don't smear too thick or it will fall off the side
  6. wait until both slides are completely dry before staining
  7. fix thin film w/ methanol (100%) and let dry before staining
• Microscope diagnosis of malaria

  • histopathological diagnosis
  • methylene blue, eosin + azure B
  • stains DNA of parasite (+ WBCs)
  • plasmodium observed in host RBC
  • Plasmodium cytoplasm = circular band (ring)
  • Plasmodium chromatin = gem on ring
• Life cycle of Schistosoma spp.

  1. eggs passed into water
  2. eggs release miracidia
  3. miracidia infects snails + produces cercariae
  4. cercaria burrows into human skin
  5. adults live in blood vessels, draining bladder / intestine
• Symptoms of schistosomiasis

  • blood in urine / faeces
  • anaemia
  • malnutrition
  • growth retardation (missing an arm)
  • abdomen inflammation + distension
• Schistosomiasis treatment

  • praziquantel - removes the invisibility cloak and kills worms
  • administered once a year based on weight/height
• Lymphatic filariasis (elephantiasis)

  • caused by nematodes
  • transmitted by mosquitoes
  • worms live in lymph glands, blocking them, leading to swelling
• What are the symptoms and treatment for lymphatic filariasis?

  Symptoms: enlargement of body parts Treatment: cocktail w/ mectizan which sterilises adults + reduce transmission.
• Arthropod parasites

  Class insecta: Fleas, lice, flies

  Class arachnida: Ticks, mites
• Global status of Malaria

  350 million people infected worldwide

  Death rate: 1 million
• Plasmodium light micrograph

  
• Trypanosoma light micrograph

  
• Leishmania light micrograph

  
• Entamoeba light micrograph

  
• Giardia spp. light micrograph