Parasitology

• Trematodes (Flukes)


  • Appear flat and leaf-like except Schistosomes which are cylindrical and elongated
  • All are hermaphroditic/monoecious except Schistosomes which are dioecious
  • All eggs are operculated except for Schistosomes which are non-operculated
  • Infective stage to the final host is Metacercaria except for Schistosomes (infective stage is Cercaria)
  • Mode of transmission is ingestion except for Schistosomes (skin penetration in water)
• If Schistosoma is found in water, its eggs can embryonate if not exposed to dry heat or sunlight
• Schistosoma needs water to embryonate while hookworm and strongyloides needs soil to embyronate
• Skin penetration in soil: Hookworm, Strongyloides stercoralis
• Requires two intermediate host except Schistosomes which has only 1 intermediate host, the snail
• The first intermediate host of all trematodes is ALWAYS THE SNAIL
• SCHISTOSOMA


  The BLACKSHEEP
• 1st intermediate host


  • Snail
• 2nd intermediate host


  • Fish
  • Crab
  • Plant
  • Snail
  • Ant
• Adults of trematodes


  • Attach themselves to the host by means of 2 suckers except for Heterophyes heterophyes (has 3 suckers: oral, ventral, genital sucker aka gonotile)
  • Function of suckers: to maintain their position where they infect
• Suckers of trematodes


  • Oral sucker (mouth part)
  • Ventral sucker (front part)
• Egg types


  • Mature when laid or operculated, embryonated egg: Schistosoma, Heterophyes, Opisthorchis, Clonorchis
  • Immature when laid or operculated, unembryonated egg: Paragonimus, Echinostoma, Fasciola, Fasciolopsis
  • Non-operculated, embryonated egg: Schistosoma
• Trematodes possess alimentary canal without anus (incomplete) unlike nematodes which have a complete reproductive system
• Trematodes possess complex reproductive structures: testes, ovary, uterus
• Life cycle of trematodes

  1. Adult flukes

  2. Egg

  3. Miracidium

  4. Sporocyst

  5. Redia

  6. Cercaria

  7. Metacercaria
• Schistosoma


  • Once the female and male worm fuse, they will no longer separate
  • Male worm has gynecophoral canal (where the female worm enters)
• Strongyloides stercoralis


  Strong and independent
• Schistosoma species


  • S. mansoni: lateral spine
  • S. japonicum: circle shape, lateral knob
  • S. haematobium: terminal spine
• Schistosomes


  • Formerly called Bilharzia
  • Adult stages are in the Blood vessel
  • Infective stage: Forked tail cercaria
  • Mode of transmission: Skin penetration
  • Schistosomule: Cercaria minus tail; remains in subcutaneous tissue for 2 days
  • Tail is highly antigenic (easily detected and killed by immune system) and is used for deceiving the immune system
• Adult Schistosoma worm


  • Have a large sucker capping the anterior end, a ventral sucker, and a gonophore, located slightly posterior to the ventral sucker
• Male Schistosoma


  • Shorter but sturdier sex and measures 12 to 20mm in length by 0.4 to 0.5mm in diameter
  • It has a gynecophoral canal where the longer and more slender female is held
• Female Schistosoma


  • Measures 15 to 26mm by about 0.3mm
  • May live for 20 to 30 years but the mean life span is much shorter (3 to 8 years)
• Schistosoma japonicum is the MOST COMMON IN THE PHILIPPINES
• Provinces in the Philippines where Schistosoma is endemic

  • Sorsogon
  • Oriental Mindoro
  • Samar
  • Leyte (most)
  • Bohol
  • Mindanao except Misamis Oriental
  • Cagayan
• Worldwide locations where Schistosoma is found


  • Japan (eradicated in 1977)
  • China (first reported case is from 1905 by Logan)
  • Indonesia
  • Philippines (1st reported case is from 1906 by Wooley)
• Schistosoma japonicum


  • Common name: Oriental Blood fluke
  • Causes: Oriental schistosomiasis or Katayama's Disease
  • Specimen: Stool
  • Habitat: Superior Mesenteric Vein in the Small intestine
  • Final host: Man
  • Reservoir host: Dogs, Cats, Carabaos (most common), other mammals
  • Intermediate host: Snail (Oncomelania hupensis quadrasi)
  • Infective stage: Cercaria
  • Mode of transmission: Skin penetration in water
  • Penetrated site: Swimmer's itch
  • Pseudomonas aeruginosa: Swimmer's ear
  • Egg: Unoperculated, embryonated
  • JAPONICUM HAS THE SMALLEST EGG
  • With a small knob-like or small lateral spine
• Pathogenesis of Schistosoma infection

  • Chronic infection: Hepatic and pulmonary cirrhosis
  • CNS involvement
  • Secondary bacterial infection with Salmonella
  • Colorectal and liver carcinoma
• Schistosoma mansoni


  • Common name: Manson's Blood Fluke
  • Causes Intestinal Bilharziasis
  • Specimen: Stool
  • Habitat: Inferior Mesenteric Vein of the colon and the rectum
  • Final host: Man
  • Reservoir host: Non-human primates
  • Intermediate host: Snail (Biomphalaria)
  • Infective stage: Cercaria with fork tail
  • Mode of transmission: Skin penetration in water
  • HAS THE SMALLEST ADULT WORM
• Schistosoma haematobium


  • Common name: Vesicle Blood Fluke
  • Causes: Urinary Bilharziasis/Urinary Schistosomiasis, Egyptian Hematuria (there is blood in urine)
  • Habitat: Vesical/Uterine plexus near the urinary bladder
  • Final host: Man
  • Reservoir host: None
  • Intermediate host: Snail (Bulinus)
  • Infective stage: Cercaria
  • Mode of transmission: Skin penetration in water
  • Specimen: 24 hour unpreserved urine sample
• Pathogenesis of Schistosoma haematobium infection

  • Chronic infection: Bladder carcinoma
  • Obstructive uropathies
  • Granuloma
  • Fibrous damage in organs
• Optimize recovery of Schistosoma haematobium in urine: Between noon and 2 pm
• Schistosoma intercalatum


  • Eggs: resembles egg of Schistosoma haematobium but can be differentiated through their eggs and acid-fast staining
  • Intercalatum has a DIAMOND SHAPED egg
  • Haematobium is acid-fast positive (color pink or red)
  • Intercalatum is acid-fast negative (purple)
  • Adult: located in the venules of colon
  • Has a diamond body (diamond schistosome)
• Schistosoma mekongi


  • Egg: resembles egg of Schistosoma japonicum but smaller
  • Adult: Located in the venules of small intestine
• Schistosoma malayensis


  • Found in peninsular Malaysia
  • Also resembles Schistosoma japonicum
• Laboratory Techniques


  • DFS
  • Kato-katz (for mansoni and japonicum)
  • FEACT
  • Urine analysis using 24 hour urine (haematobium)
  • Faust and Meleney's Egg Hatching Technique
  • Circumoval Precipitin Test of Oliver and Gonzales (confirmatory test for Schistosomiasis)
  • Antibody testing (increase in igE - represents parasitic infection)
  • Antigen detection: Circulating Cathodic Antigen (urine), Circulating Anodic Antigen (serum)
• Praziquantel


  • A heterocyclic prazinoisoquinoline compound, represents a major breakthrough in the treatment of schistosomiasis
  • Active against schistosomes both in vitro and in vivo
  • 2-3 doses in a single day
• Metrifonate


  • An alternative treatment for S. haematobium infection
  • An organophosphorus compound, given once every other week in a total of 3 doses
• Prevention and control measures for schistosomiasis

  • Chemotherapy: used when there is high prevalence, chemotherapeutic agent: praziquantel
  • Health education: to avoid fake news especially in endemic places, teach basic knowledge about transmission, symptoms, etc.
  • Control of Oncomelania snails: Focal control (identify breeding site and treat to kill excess snails), Area-wide control (long lasting effect but expensive)
  • Chemical control
  • Environmental Sanitation: latrines in remote areas
  • Integration of Schistosomiasis Control in Primary Health Care: Barangay workers should be informed about the basics
  • Monitoring and Evaluation of Control: monitor if solution is effective and if it's done the right way